Bul 627 Flammability Characteristics of Combustible Gases and Vapors

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Bulletin 627 BUREAU OF MINES

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FLAMMABILITY CHARACTERISTICS

OF COMBUSTIBLE GASES AND VAPORS

By Michael G. Zabetakis

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Bulletin 627

BuREAu oF MINEs

FLAMMABILITY CHARACTERISTICS

OF COMBUSTIBLE GASES AND VAPORS

By Michael G. Zabetakis

This publication has been cataloqed as follows:

Zabetakis, Michael George, W24-Fiammahi 1 i ty l'hnrtH'.It•rist i1'H of ('{'Jllhust ihl~ gas('..'l nnd

vttpors. r.Wnshinl,l'fon 1 U.S. Dept of t.ltb 1ntl~rim·, Bm't'>nu of l\f m es 1 1965 1

1:!1 p. lllus., tables. (U.S. Bureau of ~.Unes. Bull.l!tln 627) Includes b!bllography. 1. Combu~tlon gases. 2. Oases. 3. Vapol'!!. I. Tltll'. II. Tltll!:

Comb11stlble gases. (Series)

TN23.U4 no. 627 622.06173 U.S. Dept. of the Int. Library.

For 1ale by the SuJMtrintendenl of Documente, U.S. Government Printing Office Walhinqton, D.C., 20402 • Price 75 cent•

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CONTENTS

A he tract __________________ . _______________ _ Introduction. ______________ .. ______ . _______ _ Definitions and theory _______________ . _____ ._

Limits of flammabilitY---------------------Ignition. __ • ____________________________ _ Formation of flammable mixturf'S __________ _

Presentation of data. ___________ . ___ . _____ .. _ Deflagration and detonation processell .... _____ _

Deflag-ration. ___ .. _______ . ____ •... ______ _ Detonation _________ • ____________ • ______ _ Blast pressi.'re. ___ . _______ . ______________ _

PrevePtive measures. ___ .. __ . ______________ _ Inerting ________________________________ _ Flame arrestors and relief diaphragms ______ _

Flammability characteristics._.____ • _______ _ Par~ffi.n h_ydr?carbons •• ___ •. ________ . ___ .. _

L1m1ts 1n a1r _______________ .. __________ _ Limits in other atmospheres _____________ _ Autoignition. __________ . ______________ _ Durning rate_. _________ . _________ . ____ _

Uns~tl!ra~ed ~ydrocarhons .. __ • _______ . __ • _ Lnmts 111 air __________________________ _ Limi~s i~l.othcr atmospheres _____________ _ A utorgrutwn _________________________ . _ Burning rate .. _. __ • ___________ ._. _____ _ Stability ____ • ___ . _______ . ___ ._ ... _ ... _._

Ace~yl~mi? hy_drocarbons. _ _ _ _ . ________ . __ _ Lrmrts tn a1r _______________ . _________ . _ Limi~s i~1 _othl'r atmosplwres. ___ . _ ... _. __ . _ A lltorgn1t10n ___ .. _. ___________________ _ llurn.iug ratf'. ____________ . ____________ . Stability _____________________ .. _. _ . ____ _

Aro~nr,_tic _hyd_rocarhons_ .. _____ . ____ . _____ _ I.rmrts m arr _ .. _. _ .. _. __ . _ _ ____ .. _ .. _ ..

Pare 1 1 2 2 3 4 9

15 15 16 16 18 18 18 20 20 20 27 32 42 47 47 50 50 1)1 51 53 li3 ii5 !;() 56 57 59 59

Flammability cha~acteristics-Continued Aromatic hydrocarbons-Continued

Li.nits in other atmospheres. __ ..••• ______ _ A utoignition ___ . __ . __ .. _______ • _____ . _. _ Burning rate.--------------.-----------

Alicrc~ic ~yd~ocarbons. _. ________________ _ L1m1ts m a1r __________________________ _ Limits in other atmospheres ______ - ______ _

Alcohols.----·----------.-----------------Limits in air __ -------------------------Limi~s i~ _other atmoi!phercs ••• __________ _ AutOJgnJt,on. ___ . _________ .. __________ - _ Durning rate ________________ -----------

Ethers. _____________ - ------ _- _.-- __ -- __ . -Limits in air ____ .. ______ .. ___________ .. __ _ Limits i';l, _other atmospheres. ______ ...... __ _ Autorgnllron ___ .. _____________________ _

Este~-----------------------------------Aldehydes and ketones __ . ________________ _ Sulfur compounds ______ ·------------------Fuels and fuel blenciR ____________ . _____ . _

Ammonia and related compounds. ___ ._-_ Boron hydr idetJ __ . ______ • _ .. ______ • _____ _ Gasolines, diesel and jet fuels._._ .. ___ . __ _ Hydrogen _____ • __ . _ . ___ .• _ - __ .. _. - . - __ --

Hydraulic fluids and engin·: oils. ________ . __ Miscellaneous. ___ . _____ .. __ ..•• ______ ._._.

Acknow ledgmt>nts. __ ... ___________ . __ •. __ . __ _ Bibliography ___ ._ _ __ . _. _ .. __ ---- _--.- _-- _--App<•ndix A. Summary limits of flammability_ \pp<'IHiix B. -Stoichiomf·tric composition ____ _ Appt>llrlix C. -ll•·nt contf'nts of gascR ..... ___ _ Aprwnrlix D. --Definitions of principal symbols_ Subject index ... _--------------------------

IUUSTRA TIONS

FJ~.

I. Jguitihility cun·f' and limit~ of tlammabilit:l'· for nwthnnP-nir mixtur<'R at atmospheric preRsure and 26° C _ :.!. Eff•·et of tl'lll!Wrature ou limit~ of flnmmahility of a (•omhustihlc~ vapor in air at a constant initial pres-

surf' _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ .. _ _ _ _ _ _ _ _ _ _ __ . __ .. ___________________ .. _______________ _

a. Tin11• d .. Juy IH•forl' ignitiou of :-il'.:\' in air at 1,000 p~ill: in th•• t!'mpl'rahlrP range from 150° to 210° C._. .1 Logurid11n of t irnl' rlPlay !wfore ignition of :-i 1'.~ in air nt I ,000 psig i11itiul pr!'ssur••. _ .. _ .... _ .. - ... :;_ Simplifil'd mixl'r. _ .. _ _ _ _ ____ . __ . . _ ... __ .. .. . . . .. - .. -... --. . --- . - . ---------. - - -0. ('ompo~itiou of gas in chamiH•r :.!, fi~~:un· /i (instantaiwous rnixing) __ ........ __ . __ . ___ . _ ...... ___ .. . i. ('ornpo~ition of gas in rharnlH'r :.!, fil/;llrt' /i (d .. Iayl'd mixing) .. _ .............. _. ___ -------- ... -- .. -~ \'arint ion in Jow•·r limits of flanllnHhility of various ('Olllhustih)l's in air ll!! a function of droplPt dianwtf•r H. Flnrnrnahility diagram for th•· sy~t .. m nu•tharu~oxygPil-nitrogPn at atmot~phPril• pr••l!l!Url' ami 26° C ..

I fl. l·')llmntuhility diagram for tlw syst•·m nH·tharu~oxygl'n-nitrogl'll at atwoRplu·ric pr••ssurP and :.!6° (' . II. Etf•·•·t of init-ial t•·mpl'rutun· on limits of flammability of 11 romhustihk vapor-irwrt-air systl'rnat atmos-

ph•·ric pr•·s~un·. ___ .. _ _ _ _ . ___ . _ _ . ______ . _ .. ___ . __ . _. _., _. __ .. I:.!. EffPct of initial pn•ssurc• on limit~ of flanunahility of JP-4 in air at 26° C ..... _ ....

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CONTENTS

Effect of tomptlraturo and pr!lssurtl on limits of flammability of a oomhustlhlo vapor in R sp!loltlcd oxidont. ____________ .. _____ .. ___ .. ___ . ________ . __________________ .. _ . ______________ . ______ . _

I•'lammahlllty diagram for tho system gasolhw vapor-watm· vapor-air at 70" F and nt 212° F and atlnol!-phorio prPssur«'. __________________ .. _ .. _____ .. _ .. ___ ... ____ . ___ .-- _____ .. ___ - .... __ .. _. ___ .. ____ ....

Pr!lsl!lure produced hy lp;nition of ll 0.6 volum«'-pt•rm•nt. mPthnrw-Rir mixturl' In ll ll-lltPr oylimlPr .. _. __ _ Detonation v••locity, ~ ·; ~~ at.ic prnsAUrf', 1'.; and refll'ct.Pd prp~surP, I'" dPvt'io}wcl hy a dt'tonation

:r~d~ f!(f_"~~-t~,~~ _t!~~~~~~~- ~~~-~r~~~~~~~~x~~~~~~-'~~~~~~~~:~~_ ~~ -~ c~-~~~~c~~~~~~ ~~~~~~- ~~ _at~~~~~l-~~~~~ _ ~~~:~~_~~~~~~ Pressure variation following i~:nition of 11 flammllhle mixtur«' in unprot .. ct.Pd nne! protPelo•d Pllclosureij .. _ PrPssuro producPd by ignition of 11 tlarnmalle mixtur" in 11 VPnt ... d ovt•n ..... __ -. _ ..... __ . _____ . __ _ Effect of molnculnr WPight on lowPr limits of llnmmahilit.y of parntfln hydrocnrhonH &t ~5o C _____ . __ Effect of tt,mperature on low!'r limit. of tlnmmahility of tnt•t.hnnt• in l'.ir nt nlllH18p!u;rin prPHHilre. _ .. __ _ Effuct of tPmperature on lowPr limits of tlammnhilit.y of !0 pnrnffin bydrotlllrhons Ill 11ir nt ntmosplu•ric

E,r;;~r~~mpPraturc on lowl'r ·ii,;,it.s of IIHmmahility of 1 u purut-ti,; it~.-,1,-ucnri,~;.~-i;,- ;,;,- ;, (. ·n·,_;,;u~ 1~!;,~~~;. Ett:::So~r~'e,~~e~":~~~~;~;;; L-,i i,~~~-rati~ -o-fpt~~;tii~; i~.Y~l~~~~rl,o;;~ i;~·,;ir ut. at.r;,;,~pl,i·~ie-pr(;~u~;.- ~ ~. ~-: ~ Effect of tempemture on l! tiC' a~· r.ttio of pnmflin hydro<"nrhons iu nir at nt.nw~plwri" pt'l'HHure in thu

absenc<' of cool flam<'"---------------------------------·----- ... ____ - ----- ___ ..... -Effect of pressure on limii-H of llammitbilit.y of pentmw, lll'xane, and lwplnht' in air at 26° c __ .. _ .... __ .. Effect of pressure on limits of llnmmability of natural 11:11~ in air nt :.!So C ______________ . ___ .. ___ - __ _ Effect of press:.~re on lower temperature limib of fh1mmahility of pontnnl', hcxam•, heptane. nnd odane

in uir ___ .. _____ .. _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _____ . _____ . __ ... ___ . _ .. __ ... _______ .. ______ .. ___ .. ___ .. __ Limits of flammability of vnriouH methane-inert ~:tA-nir mixturps tit 25° C anrl utmospheril' pressure __ _ Limits of flammability of Ptlmne-cnrbon dioxi!IP-air and cthm;e-nitro~cn-nir mixtures 11t 25° C and

atmosphnric pressure .. _________ .. ________ .. ___ .. ______ .. _ .. _______ .. ___________ .. __ .. ___ ....... __ - _ .. -Limits of flammability of propanu-rnrbon dioxide-air and propanc-nitrogen-nir mixtures nt 25° C nne!

atmoBpheric pressur(l ........ __ . _ .. _______________ .. __ ... ___________________________________ - __ _ Limits of flammability of butane-cr.rbon dioxide-air and buta, e-nitro~en-nir mixtures at 25° C nnd

Li~\~o~r~c;;::~~hifi~~eof -~n~lo·t~s- ~=p~~t~~~~~-i~~~~~ ~;l;:t~i; -~~~~tt;;, ~-~~t 2-5°- C- i~~~~-~~tt~~~ph~;lc- p;~;s~1~c ~ I.irnita of flammability of various n-hcx:me-inert p;as-nir mixtur ·H nt 25° C and atmospheric pressure_­Limits of flammability of n-hcptune-watcr \'apor-air mixtures at 100° and 200° C and atmospheric pressurr ___________________________ , __________________________________ .. _________________ _

Appro"•~.u1te limits of flammability of hiv,hPr pamffin hydroenrbons (C.ll~o+a• n~5) in carbon dioxide-lllr and nitrogen-air mixtures at 25° C nnd atmospheric press•1rc. ________ .... _ .. __ .. ____________ - .. __

Effect of pressure upon limits of flammability of naturnl ~~:as-nitro~en-:tir mixtures at 26° C_- ___ -- .. _-Effect of pressure on limits of flammability of ethanP-carbon dioxide-air mixtures at 26° c_---------Effect of pressure on limits of flurnmnbility of ethnnu-nitrogen-uir rnixturus :tt 26° C ___ .... _______ - __ -Effect of pressure on limits of flammability of propunP-earbon dioxide-air mixtures. _____ .. _______ - .. _-Effect of presHure on limits of flammnbilit.y of prop:uw-nitrogen-air mixtures._ .. __ .. __ .. _______ .. _ .. - __ _ Effect of pressure on minimum oxy~~:en requirements for flume propap;ation throu~~;h natural gas-nitrogen-

air, ethanc-nitrop;c•n-air, und propune-nitro~Pn-air mixtures nt 26° C ________________ .. _______ - . __ Low-temperature limit of flammability of dccmw-uir, rlodeeane-uir, and decune-dorleeane-nir mixtures. Minin.mm uutoignition temperatures of paraffin hydrocarbons in air us a function or uvernge carbon

chum length ______ .. _______ .. ____ .. _______________ .. __ .. ___________ .. _ .. --- _--- ___ -- - --- - -- ---- .. Burning velocities of methnne-, ethane-, propane-, nnd n-l~eptane vupor-uir mixtures ut atmospheric

pressure and room tnmperu~Uf(l_ .... __ . _________ .. ____ .. __________ .. _____ - _ .. _-- _ .. __ - .. - ... - .. ------Burning velocities of methane-, ethane-, nnrl propnne-oxygcn mixtures at ntmospht'Tic pressure and room

temperature ________ . __ .. ______________ .. ______ . __ .. ____ .. _____ .... ______ .. __ .... _____ - __ .. __ ------Varint1on in burninp; vplocity of stoichiometric methane-~ir and propane-air mixtures with pressu1•: ut

26 ° c- -----.. --. - -.. -- -- ----. ---------. --------.. ----------- . - .. ---- ---- .. --- ---- ------------Variation in burning velodty of stoichiometric mcthnne- und ethykne-oxvgen mixtures with prcssurt:

at 26 ° C _______________________ . __________ .. ______ .. __ .. ___________ · ___ .. _____ .. _______ .... ___ .. __ Effect of temp<"ruture on burning veloPitiPs of four paraffin hydrocarbons in nir n.t atmospheric prl'ssure. Detonntion veloeitieH of nwtlmnc-air mixturPs 11t atmospheric prcMsurn_ .. ________ .. _ _ _ _________ - __ -Deton~tion velocities of methane-, ethane-, propane-, butnne-. and hexane-oxygen mixtures at u.tmos-

phenc pressure.__ _ __ . __ .. _ .. ____ .. ___ .. _____ .. ___ ...... ___________ .. _. _______ .. - - ____ ----- __ .. -----Detonation velocitit•!i of n-heptane vapor in WFN A (white fuming nitric ncirl)-nitrogen gas mixtures ut

atmospheric pressure and 400° K .. ___________________ .. __ .... _____ .. ___ .. _______ .. _____ .. _______ .. __ Relation but ween liquid-burning mtc. (lur~P .. pool diameter) nnd ratio of net heat of combustion to

sensible heat of vnporizn tion. ____ . __ . ___ . ____ . ______ . __ .. ______ .. _ _ _ _- -- _--- .. --- - -- - .... -- - - - -Elfeet of tem)ll'rature on lowPr limit of flamnlllbility of ethylene in air at atmospheric pressure .... _-_--Limits of flammnhility of ethylene-carbon dioxide-air anti ethylene-nitrogen-air mixtures ut atmosph(lrif'

pressure and 26° C ______ .. _____ .. _ _ _ _ .. _ .... _________ .. _ .. ____ .. ____________ .. __________ .. _____ _ Limits _of flammability o! bropylene-carhon dioxide-air anrl propylene-nitrogen-air mixtures nt atmos-

Lit;ll:::~~r~~;~~~~~~:bHlt;6 of' -i;~bt;t·y-h•;l~~:,:a-rh~~; '(ii;,~;(j~--a-i~- ;1~;1- -i;~,;lltyie~-;_,:~it~~K~l~::;i;- ;l;lx-t~l~~~ -,~i: Li:~\':~o~r::::%cn~;~l1;m~;(:)r11i1~~~;~:y?t,~~~~;lt~;: ~;;po-r~~~y~~~ ·,;ll~tu"r~'~ -,~t-l.~(l0 c- ~;1;1-t~tlllORpll;.~i • .- p;:~s~;.~~-: Limit~ of flammability of butcrw-1-('arbon dioxidu-air anrl butune-1-nitrogen-air mixture~ at lltmosplwrie

preHtiUre lllld 26° C .... ________ . ___ ... __ .. ___ .. ____ .. _. __ . _ .. ___ ... ______ ... _____ . _ .. ______ .. ____ _ Limits of flammability of :i methyl buterw-1-carbon dioxide-.Lir and 3 methyl-butcne-1-nitrogcn-air

mixtures at lltmoepheric preliSUrc u.nd ~6° C ... ____________ .. ________________ • ______ ...... ____ -----

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CONTENTS

LirnitR of flummubility of buttLdiene-c~trbon dioxide-nir :md butadiene-nitrop;cn-air mixtures at ntmoe-

Ed:~~r~r r~b~~~~~~~':.~~ll;6:n~oitlt;l-pr~s~~~~-~ -r~l~l(;iro~~~;~t~ -f~r -pr"Op,;g,;tl~~ -0,- clcft~g~~tl~il-l~~d-d~tonatii1;1 through neetylenn gtlH ......... _ .. _________ .. ______ .. _ .. ___ -- _-- ___ .. - .. - .. -.-- .... ----- ..... - _--- _- .... ___ _

ll.nn~~:e of flammnble mixtures for methylacotylene-propadione-propylene systmn at 120" C and at 50 and 100 psig_ --··-------------·--·------------···---- .. ------··· ------- ................... ..

(~ucneherl limitli of flamrmli.Jilit.v of nc:etylene-enrhon rf;,)xiJe-ILir ILnd ~tcetylcne-nltrogcn-air mlxturetl 11t atmospheric pn•HKllrt' and 2!1° C obt11inecl in n 2-inch tube __ .... _ .... ___ .................. ___ .. __ .......... _ .... ..

Miuiu~<lrn nut.oi!(niti"l' LcrnperaturcR of ncPtylenc•-air nnd ncetylene-oxyp;en mixtures at atmospheric cmd devnterl pressureR .... _ .... __ .. _____ . _ ...... _. ___ ...... __ .... __ .............. _ .. _ .... __ ................ - .... ----- .. -- .... ..

Burning vl'loeit.y of tu:etylene-11ir mixtures at ntmospheric• pressure anrl room temperatuw ...... ___ .. __ .. .. .:\faximurn /,/ D rutio rc•quirerl for tmnHition of 11 deftagrntion to c. detonation in acetylene vapor at 60"

F and from 10 to 70 psia ______________ -· -------------------------------------------------Final-to-initial pressure ratios developed by neetylene with det.onati,m initiation at ·;arious points

ntonf( n tube __ ...... _ . __ . ___ .... _ .. _ . _ ....... __ . _ ..... _ ........... __ .... _ ...... - ...... - ......... --- .. --- .. - . Limit.~< of flumrru;bility of benzPni'-IIIPthyl hromiclt•-:lir mixtures at 21>" C and benzene-carbon dtoxidt ... air

ancl IH'IIZI'IH!·nitro!(cn .. uir mixturPH at :.!!i 0 und 150° C and atmospheric prC88Ure ........ __ .......... _. _ ....... . Limilt! of flammubility of II 3 0~-C,li,.(CIJ 3)~-11 30 ut. 154° C und 1 ntmosphere pressure _____ ----- ___ _ Limit,; of flammability of 90-weight--pcrl'l'nt l!~02-C0 II,.( Clh) 1-IICOOH at 154° C and 1 atmosphere

\lf!'HSliTI' ..... -- _ .. _ .. _. __ .. _ .... _ ... __ ..... _ .. _ ....... _ .......... _ .............. __ .................... _ ......................................... ..

Minimum uutoignition tPmpcrutures of ttromntic hydrocnrbons in air ns a function of correlation par:under D., ____ ...... __ .... _ .. ____ . __ ... _. ______ .. ____ . __ .. __ .. __________ .. _________ .. ___ .. ___ ... _

Limit~!'! of fl~1rnn~ability of ."~~·lopropane-earhon ~lioxiclc-air, cyclopropane-nitrogen-air, and cyclopropane-behum-utr nuxturPs at 2o C and utmosphcrw pressure .. __ .. ____ .. ________ .. ___ ._ .. ___ ........ __ .. _ ...... __

Limit!:! of flmnmability of cyclopropanc-helium-oxy~en unci cyclopropane-nitrous oxide-oxygen mixtures at 25° C and atmospheric preRsurc. _. _ . ___ .. _ .. ______ ... ___ .. __ ....... ___________ ... ______ .. __ ...... __ .. _ ..

Limits of flammability of cycloprop:mc·-lu•lium-nitrous oxide mixtures ut 25° C and nt.mosphl'rir pressure. Limits of flammability of methyl alcohol-carbon dioxide-air and methyl alcohol-nitrogen-air mixtures at

25° C and a tmosplwric pressure_ .. ____ . __ . __ .. ____ .. _ .... ___ .. ____ .. _ .. ________ . _ .................................. .. Limits of Flammability of methyl alcohol-water vapor-air mixtures at 100°, 200°, and 400° C and

tl' ·nospheric pressure __ .. ___ .. __ . _ ... ___________ .. __ .. _ ..... _ .. ____ .... _ .. _ .. __ .. ________ .. ____ ........ _ .. __ .... Limns of flammability of ethyl nlcohol-carbon dioxide-air and ethyl alcohol-nitrogen...air mixt,ures at

25° C and atmospheric pressure _________ .. _______ .. ______ ------------------------------------Limits of ftnmmnbility of ethyl alcohol-wut:·,· vapor-air mixturee at 100° C and atmospheric pressure .... Limits of flammability of tert-bu tyl alcohol-wtttc·r vapor..nir mixtures at 150° C and atmospheric pressure .. Limits of flammability of tert-butylalcohol-curbon dio'l:idc-oxygen mixtures at 150° C and atmospheric

prcssurP ___ .. __ . _ ... _. _ .. _ ... ___ .. __ .... _____ .. _______ .... ___________ .. _ _ _ _ .. ________ .. ___ .. ___ .. _ .. ___ _ Limits of flammability or 2-Pthylhut.anol-nitrogc>n-oxyg••n mixtures at 150° C and atmospheric pre88ure .. Limits .?f flummuhility of dimc>thyl etlll'r-curbou dioxide-air and dimethyl ether-nitrogen-air mixtures at

2.'}0 C. and at.mosplll'ric \>rPH~ttre _________ ............... ------------------------------------------Limit!l of flammability of c icthyl Ptlll'r-carbon dioxidc-air and diethyl ether-nitrogen-air mixtures at 25°

C and ntmo~plwric pr<'ssnre _ .. _ ... _ . _ _ _ .. _ . _______ ... ___ .. ____ . _ .. _ .. ______ .. ___________ .. _ ... __ ....... _ Limits of flammability of di!'lhyl PtlH'r-hdium-oxygen and diethyl ether-nitrous oxide-oxygen mixtures

at :.!5° C :md atmosplwric pr<·ossllr<'. _.... _ .. _ .. _ .. __ ... ___________ .... _ .. _ .......... _ .. - ....... - ......... ---------Limits of flnmrnnhility of dif'!hyl PthPr-uitrouH oxiclc•-helium mixtur<'S at 25° C and atmospheric pressure_ Limitt! of flammability of nwthyl formntP-cnrhon dioxiclc•-air and nv>thyl formate-nitrogen-nir mixtures_ Limit 11 of fl!unrnabilit y of isohtl t yl formatP-cnrbon dioxi•lc•-air and isobutyl formate-nitrogen-air mixt.ures_ Limits of flammability of mt'thyl ac·l'tat•·-t•arhon rlioxiclc·-air tmd methyl aeetttte-nitrog"n-air mixtures __ Etf .. ct. of tt•mpPraturP 011 lowt•r limits of flnmmubility of MEK-tolucne mixtures in air a.t atmospheric

Ed:~~~~~t;;.;,;,;;r~;t~.~;. -~~~ lo~;c:r li;~i-ts-oi fi,;rr.;l~liiitity- of-Tii ~'=t~i~t~;l~- ~i~tt~rcs ~~ -~ir-~t ~-t~o~ph~~i~ pr .. ~su rP ... _ . .. . _ .... _ .. __ .. _ . .. . .. . _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ .. ___ .. __ . ___ .. _____ .. ______ _

Effptt of liquid t'omposition on lcwPr limit~ of flammability of MEK-toluene mixtures in air at 30° attd 20\.1° c ___ . _. _ ..... _ .. _ .. __ .. _ ... _ _ .. .. . ___ .. ____________ ...... ___ .. _____ .... _ .. ___ .. _____ ... ____ .. ___ _

EfTet·t of liquid cmnposition on lowt•r limits of flammability of TIIF-tohwne mixtures in air at 30° and 200 . c .. - .......... - - - . -- .. --- .. -.... --- .... -- -.. - .. --. - . ---- .. - - ------..... - -..... ---- .. -... - .. - ... -- ... -

Limit !'I of flnmmabili:y of aePtoru•-rnrhon dioxidc'-air and tlCI'tOtH'-nitrogt•n-nir mixturc•s_. ___ ... __ .. _.-LimitR of flammnhilitv of nwthyl Pthyl kl'lonP (l\II~K)-chlorohromomethant' (CBM)-air, MEK-carbon

clioxiciP-air ancl l\H~I\-uitro~tPn-nir mixtHr<'S nt. 25° C and atmosplwric pressure ____ . ___ ... ____ .. __ _ Limits of flamnmhility of enrhon disttlfidP-eurbon dioxidc·-air, carbon dioxidt•-nitrop;Pn-nir mixtnrPsnt 25°

C nnclat mosph<'rie prP~snr!', unci e.nhon disnlficl<'-watPr vapor-nir nt 100° C and ntmoRpht•ric prt•sRnre. Limit:-~ of flammnhility of hydro~o:Pn MulfidP-enrhon dioxide-nir mixtures nt 25° C and ntmospheric

prPs~<ll r<' . _ _ _ _ __ . _ .. _ _ __ .. _ _ _ _ ... _ .. .. ___ ... ____ .. ___ ...... _ .. __ . _ _ _ .. _ ... __ .. _ _ .. _ _ Limits .of tlummnhility of l'thyl mt•rc•nptan-F-12-air and Pthyl mcre:Lptan-F-22-nir mixtures nt atmo~ ·

(lhl'fll' pri'HHIIrP 111111 27° C ..... _.. . .. ... . _ ... _ .. _ ...... _ ...... _____ .. ____ . _. _ ...... _ _ _.... _ .. _ Limit>< of flnmmnhility of nmmoniu, l;D:'Illl, :'11:\111, and hydrnziul' nt atmosplwric prt'SI!ure in saturnted

IIJHinPnr-!mturntP!I vnpor-nir rnixturPs____ _ .. .. ......... ____ .. ..... ..... ..... ......... .. ... -FlnmmnhiP mixtnrP c•ompositiouH of hyllrn7.iru·-lwpttuu'-tlir nt 125° C tmd approximntPly ntmoHplwric

pri'S"II rl' ...... _ _ _ _ _ . _ _ _ .. _ .... _ .. _ .. . __ .. __ .... _ ..... _ . _ ..... ___ . _ .. _ .. __ .... ___ ......... _ ........... _ .. _ :'lllllimmn spont:wPons i;cnition IPIIIJWrttturt•s of liquid hyclrnzirw, 1\11\111, and Ul>l\111 at an initial

tc•mp••raturP of 2!i0 (' in C'Onttu•t with ]I;O,•-ttir mixtun•s nt 740 J: 1tlmm Hg as a funetion of l'\01•

c•onc•l'lltration. ........... ...... ................. . .......................................... ___ .. :'lliuimum HpontttrH'OUs ignition t•·mpPrnturPH of liquid hydrazirw at various initial t.Pmpt•raturc'l< in

l'\'01 •-air mixtures at 740 !10 mm H11: as a function of NU1• concentration_._ .... _ .... _ .. _ .. _. _- ...

v

1'-.e

55

56

57

58

58 59

59

60

61 62

63

64

65

66 66

66

67

68 68 68

68 69

69

69

70 70 71 72 72

73

74

75

71) 77

78

79

79

711

80

IH

s·•

..

Vl

J'tl, 102.

103.

104.

lOIS.

106.

107.

lOS.

109.

110.

ill.

112. 113. 114. 11/S.

116.

117.

118.

119.

120.

121.

122.

123. 124. 125.

126.

127.

128.

129. 130.

131.

l~ONTENTS

\llnlmum 11pontaneoue Ignition temperature~~ of llguld MMH at various Initial tomperetur~>.e In N01•-air mixturtlll at 'l40 ± 10 mm Hg n11 a function of N02• oonc(mtration. __ . _ ... _________ . ____ . _____ ..

Minimum spontanooua ignition temperatur011 of liquid UllMH at various Initial temperatures in N01•-air mixturce at 740 ± 10 mm Hg as a function of N01• conccntl'ation .. ________ .. ________ .. _

Minimum spontaneous ignition ternperaturlll! of 0.05 oo of liquid UDMH in llc-OrN01• atmoephl!ll'llll at 1 atmosphere for various lle/0

1 rati011 .• ____ . ____ ..... _. ___ . __ -. _.-- _- __ .. __________________ . _

M~~d"~;;' ~r.~a:fu~~t'/!;~i~r'N~:~~~:!~~~a~fo~·~~ .. c_c_ ~~ !~~~~~ -~~~~~- ~~ .~~·-·~~~- ~~~~~~. ~-t- ~~ Minimum spontaneous Ignition tempN'aturoo of vaporb;ed UDMH-air mixture~~ in contact with 100

pet N01• at 25° C and 740± 10 mm Jig u a runctlon of UD MH concentration In air. ___________ _ Limite of flammability of dlborane-ethane-air mixtures at laboratory temperatur• and 300 mm Hr

AJ~~~~~~~m.~r:n ~u-r~;,a £~;:: .4~-.-~iaiio~ ic~~ilnc: 8Ta<l~ i ooii ao; -8; ·a-~laiiO'n ·;ai0iii1e: · iiacie-i faii 4&; C aviation jet fuel, grade Jr-1; D, aviation jet fuel, grade JP--3; and, E, aviation jet fuel, gnde JP-4------------------------------------------------------------------------------------Limlts of flammability of aviation gasoline, grftdes 115/14/S vapor-carbon dioxide--air •nd 116/14/S vapor-nltroRen-alr, at 27° C and atmospheric prll6Surc _____ . _______ . ________________________ . __

Limite of flammability of JP--4 vapor-oarbon dioxide-air and JP-4 vapor-nitrogen-air mixtures at 27° C

Li!~~ ~r~~:;~~,f;~~~rhrdrogen~e&r'bo~- -;:ii~iid~~~.: -.-~d -hi<iroi•;n~rltiro.ie-~-~i.: -.nixiur~- ~t: ·isci -d and atm011pheric prtlllllurc •• _. _ • _. __ .•. _- _--- __ - -- - - --- ---- - . - --- .. - -- --- . - . - -- -- . - - -

Limite of flammabiht.v of Hr NO-N 10 at approximately 2R° C and 1 atmoeph.,,·c. _________________ _ Limite of fiammabi!it.y of HrN 10-air at approxlmat~>ly 2R° C ~tnrl 1 atmosphere. _________________ . _ Limite of flammability of H,-NO-air at approximately 2R° C and I atmosphere._. __ .. _ . ____________ _ Rate of vaporiaat.ion of liquid hydrogen from p11raffin in a 2.H-inch Dewar ftuk: Initial liquid depth-6. 7 Inches _____________________________________ . _ . ___ . __ . _______________________________ _

Theoretical liquid regr088ion rates following !!pillage of liquid hydrogen onto, A, an average soil; B, moillt sandy eoil; and C, dry sandy soiL ___ .. __ .. __ .. ___ .. __ . __ .. ___ ... ____________ .. _________________ _

Theoretical decreue in liquid hydrogen ll'vel following l'pillago onto, A, dry sandy soil; B, moist sandy soil; and C, an average soiL ___ - __ ._._-- __ .... -- ... - ... - . -. ---.----- . ------- .. ---- .. ------------

Extent of flammable mixturlll! and height of vlsiblc cloud formed after rapid !!pillage of 3 litera of liquid hydrogen on a dry macadam 11urface in a quieact"nt air atmo~flhere at 1 :S" C _______________ .. ____ _

Motion picture sequence of villible clouds and flames resultinR fron. rapid spillage of 7.8 litera of liquid hydrogen on a gravel surface at 18° C. __________ .. __ . ________ . ________ ... _________________ • __ _

Maximum flame height and width produced by ignition of vapor-air mixtures formed by sudden apil-lap;e of 2.8 to 891it!'rs of liquid hydrogen ________ ·--------------··----------------------------

Burning rates of liquid hydrogen and of liquid methane at thf' boiling points in 6-inch-Pyrex Dewar fluke ____________________ .. _________________________ .. ____ . _ .... ___________ .. _______________ _ Variation in minimum ftutoignition temperature with prei!Bure of commercial phosphate ester and

mineral oil lubricftntd in ~tir in n 450-cc-atainletll! steel bomb. _______ ... __ . _________ . ____________ _ Logarithm of initial pr!'8sure-ATT rat;.o of seven fluids in air for various reciprocal templ'raturcs. ____ _ Variation in Tr/ T; of air with V,f Vr and with P1/ P; in an adiahatic compression procesM .. ___________ _ Variation in air temperature with P,/P; in lln adiabatic compr088iou process for five initial air tcm-pl'raturE'S. __ . _____ . ______________________________ . ____________________________ . _________ _ Limit!! of flammability of carbon monoxide-carbon dioxirl<~<air and carbon monoxid~.-'-nitrogcn-air

mixtures at atmospheric pressure and 26° C _ . __ . _____________ .. _____________________________ _ I.ower limite of flammability of N PN vapor-air mixturlll! over tlw pressure range from 0 to 1,000 psig

F.::n?::bl~ 2~ i>~5~:~~~,:i;~:i~tu.=~- ioim~-o~~.: iii.~-pr~~~-~ -r-ariic. rion-; o-io -~ ~ooo-p;ig- at~ 5o"-and 125° c ________________________________________________ . ---------------------------------

Variation of explosion pressure following spontanoouM ignition with N PN conct>nt.ration. _______ .. __ Minimum spontaneous ignition and dccompOI!ition tcmp<'raturcs of n-propyl nitratl• in air as a func-

tion of P.ressure ______________________ . _ . __ .. ______ . ___ . _ _ _ _ .. ___ .. ____ . _ .. __ .. __ .. ___ .. _.- .. - _ .. Flammability of trichloroethy le::~c--alr mixtures. ___ .. ______ .. ______ . _______________ .. ___ . _________ . _

TABLES

84

8~

80

87

117

88

HH

lUI

HH

80 .ill Ill IJ2

93

U3

94

!14

95

96

96

!18 !l!l

100

101

102

102

10:} 104

104 105

Pare 1. Conditions of failure of peak overpr-urc--lll'n8itiv<' ell'ml'nta _____________ .. ___ . _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 17 2. Propertlee of paraffin hyrlrocarbona __ . _ . _ _ _ _ _ _ . . . _ . _. _ . _ _ _ . _ _ _ _ _ _ _ _ ... ____________ . _ _ 21 3. Uppl'r flammability limit~ of m!'thanc-air mixturf'l! llt IIi p11ig _.. __ .. ___ .... _ .. ___________ .. _ _ _ _ _ _ _ _ _ _ _ 24 4. I.owcr t!lmperature limi~ and autoiguition t<·mp1.•raturt•s of paraffin hydrocarbons at atmosphl•rle

pr-ure __ .. _ _ _ _ _ _ ________ .. ________ ... _ . _ . ___ . ___ ... _ _ _ ____ . _ .. _ _ _ _____ . ______ . _ _ __ . __ .. 25 5. Limiteofflammahilityofml~thanoinchlorinP __________________ --------------·--·-··---·-·- 'J.7 6. Limits or flammability of Pthane in chlorlnl'.-- --- -.-----.- ------. ---.---------------.------- 211 7. Properti('!l of unaaturatNI hydrocarbonH __ . _ . . _____ . ___ . ___ . ______________ . _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 4H 8. Limit" of flammability or unsaturated hydrocarhons at atmosphl'ric pr!'lllurr and room t~>mprraturc, In

volumt'-p~>rccnt combust! hiP vapor ___ . . ___ .. __ . _____ . _. _____ . ___ . _ _ _ _ _ _____ . ___ . _ _ ___ . _ _ _ _ 52 P. Minimum autoignitlon temp!lr!lturee of unsaturated hydrocarbons at atmospheric prc881Jrr .. _____ ..... _. _ 52

10. Heats of formation of unsaturated hydrocarbons at 2/S0 c ___________ ·----------------------------- li:i 11. Propertlea of selected aromatic hydrocarbona. _______________ ... ______ . _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 60

..

CONTENTS

12. Pro~'''rtiCB of at>leoted alicyclic hydrooarbono ............ _ ....... _. __ .. ___ ..• _ ..... _ ........................................ . 13. Propertil'll of selectt>d. simple alcohol!! ........ _ .............. _ ............ _ ............. _ .............................. . 14. Propprtif'8 of selected ethers .. _ ........ _ .. _ .......... __ ..................................... --.-- ... - ....... ---.- .. .. 15. J>rop!'rt.if's of &f'l!'ctcd estt•rs ....... _ .. _ .... _ ..... _ ......... _ ................................ - -- .. - .................... . 16. Proper! iPs of sl'lccted aldnhyd!'s and ketones .... _ • __ .• _ .. _ .. _ .• _ .. _ ....... _ .............. _ ..... _ ... _ .............. _ ... 17. J>ropt>rtil's of lll')ectf'd sulfur compounds_ .. _ ......... _ ............ _ .. ____ ............. _ ...... _ ................................... .. I H. l'ropt•rti!•s of st•lectf'd fuPI.I! and fuel hil•nds ........ _ ... ___ .. _ .. _ ...... _ .. __ ... _ ............ _ .... _ ....................... _ .... .. 19. Limits of flammability of ammonia at room tPmpl!rature and near atmospheric prt'88ure ..... _ .............. . 20. A utoignition tPmpt•rature value11 of various fuP)s in air at I atmosphPrt•.............. . .. .. • .. . .. . . .. .. ........ _ ....... .. 21. Limits of flammability of hyrirog!'n in various oxidant!! at 25° C and atmoaplwric prl'&llure ..... _ ........... .. A-I. :o;urnmary of limits of flammability, Jowf'r tempPraturc limits, and minimum autoignition temperaturC8

of individual g11.11e11 and vaport:1 in air at atmospheric ptllii8Ure .................. _ ... _ ............ _ ......... ..

VD

~"••• 6 .. 67 70 71 73 7" 77 7R 88 8\}

11 ..

FLAMMABILITY CHARACTERISTICS OF COM­BUSTIBLE GASES AND VAPORS

----------·--------------·------------·---·---··-··-

Abstract

THIS is a summary of the nxailablt> limit of flammability, &utoignition, und buruinK-ratt> dtLtn for more thun 200 (~ornbustible ~ase.s and vapurs in uir nnd other oxiduuts, ns \n'll as of empirical rules and g;-aphs that

Ct\11 be used to predid similnr dnta for thousands of other eombustibles u:1der n \·uriety of environmental conditions. Specific. data are presented on the pnrutfinie, unsuturntl'd, arornntic. tLnd tLlieydic hydroearbons, alcohols, ethers, aldehydes, ketone..'>, nnd sulfur contpoun<ls, nnd an assortment of fuels, fuel blends, hydraulic fluids, engine oils, and miseellaneous combustible gases and vapol'8.

I ntroductt:on

Prevention of unwanted fires and ~a..~ explosion disastern require.• a knowledge of flammability characteristies (limits of flammability, i~nition requirements, and burning rules) of pertinent eombustible ~ases and vapors likely to be encountered under various conditions of use (or misuse). A-•uilable data lllllJ not always be udequate for use in n partieular application since they may htn·e been obtuint>d at.!! lower temperuture ».nd pressure than is eno)unt.ered in practire. J<'or exnmple, the qunntity of air that is re11.uired to d-,wrcal$(1 the eombustible vnpor ronrcntrntion to u safe le,·el in ,._ purllcular pro(·ess l'arried out at 200 oc should be based on flummability data obtnined at thts tempemturt>. When these are not a\·ailable, suitable approximations can be made to permit a realistic evaluation of the hazards assoriutf'd with the proces..o.; bein~ eonsidert>d; such npproximations can serve as the basis for de:-:i~;,ing suitable saff'ty dPvires for the proteetion of personnel and equipment..

The purpose of this bulletin is to present a general rt•view of the subject of llnmmnhility, and to supply sE.'lect expt•rimentnl dllta tmd t'mpiri('IAI rules on the fltunmabillty charu<·teristirs of various fumilies of combustible gase..~ and ,·apors in nir and other oxidizing utmospheres. It eontains what are belie,·ed to bA the lutest and most relinhle dntn for more tlum 200 combustibles of intere:o.t to those concernE.'d with tht• pren'lltion of dis~tstrous gas t~xplosions. ln nddit ion, the empirienl rull.'s und grKphs prl'sen tl'd here ean bt~ used to predil'l similnt· da tn for other ('Om bust ihlf's under a \'ILri~ty of coradit ions. This bulletin supplcntl'nls Durf'llU bulletins (40F nnd otlwr ptihliclltions (1li8).

Basi<' knowled~e of comhustion is dc·:-;irnhlt• forti thorough unde~tllnding of t hi' llltltt'riul, which t'llll bt- found in numt'rous Jmblit'at ions (6.CI, 1.9.9, 1!02). Tht-refore, only thost> nspt•l'ls rt>quired for an un e~tanding of flammability are considered here; t'\'1'11 tht>se nrl' considert'd from a fairly t~lt~rnt~ntllry viewpoint. ' •

IJ'hyslcw chemist. pro)eet coordinator. lias Expl<l$lon.'l, l!xpllliiV .. R-..rt"h l't'ntor. n~uo!Ninea. PIUaliUI'Ih. , •• •ltallcl&ed numl>tVI In partonth- R>lor to hNna In tho blbll..,-aphy at tho end ol thlt rt'INII1

Worll: on maouacrlpl oomplele<l Nay 10114.

1

l<'LAMMABJLITY CHARACTERISTICS OF COMBUSTIBLE OASES AND VAPORS

DEFINITIONS AND THEORY LIMITS OF FI..AMMABILITY

A combustible gl\8-l'.ir mixture can be burned over a wiie range of concentiations-when either subjected to elevated temperatures or exposed to a cat.alytic surface at ordinary temperatures. However, homogeneouc; com­bustible gas-air mixtures are flammable, that is, they can propagate flame fre~ly within a. limlted range of ~umpositiollS. For example, traco 1\mounts of methane in air can be readily oxidized on a heated surfane, but a flame will propagate from an ignition source at ambient temperatures and pressures only iC the sur­rounding mixture co['Jtain!l at least. 5 but less than 15 volume-percent methane. The more dilute mixture is known as the lower limit, or combustible-leu.v limit, mixture; the more COflcentrated mixture is known as the upper limit, or combustible-rich limit, mixture. In practica, the limits of flammability of ~~ par­ticular system of gases nre affected by the tempernture, pressure, direction of flame propn­gation, gravitational field strength, nnd sur­roundings. The limits are obtained experi­mentall~ by determining the limiting mixture compositions between flnmmable nnd non­flammable mixtures (244). That is,

and LT.P= l/2[C,,.+Cttl.

UT.P= 1/2[0,,+ Ct~l.

(1)

(2)

where LT,P and UT.P are the lower anti upper limits of flammability, respectively, at a speci­fied temperature and pressure, C," and e11, are the greatest and least concentrations of fuel in oxidant that are nonflammnble, and C11 and ell! are t.he least and grentest concentrations of f11el in oxidant th11t nre flnmmnble. The rute at which n tlnme propttgates through u flum­mable mixture depends on tl number of ft~ctors including Lemperuture, pressure, tllld mixture <'olllpPsition. lt i!-. a minimum at the limits of llummabitity nnd n mnxirnum tll netu· stoichio­metric mixtures (1:30).

The Burel!u of Mines has udopted 11 st undu.rd npprtrtttus for hmi!-of'-flumnwbility dett•l'lllirut­tions (40). Origirutlly designed for us<• at 11 tmo;,p/ierie fWCHsun• and room t ('Ill pem tur·p, it wus lutPI' modilied for u:,.;c tli. redt:eed pr~s­,;m·es by inrorporutin~ tl spurk-~np ignitor the hns!' of tlw 2-inl'h, g-lass, llnllH'-J)ropag-ution tube. This nwdifil'ntion introdU<'I'I a diilil'ult thnt wns not iilillll'di,ttPI)' uppnrent, us tlt.P spnrk PnPrgy wus not ttlways ad1•qunte for· usp in limit-o~ 1' llllllluhility dPtl'rminations. FigmP I illustru.o . ti1P pffPI'I of mixturp co:upo,.;ition on t hP eleetrienl spark ener!!,y re!{Uir·erneub for

r ~ I :. .8 VI .6

.4

L_ Limitsof~ ~-flammability----Jl 1 ~-Aonitlbility J X limits-----...

~

\ X""<.,.x

·~~~4---6~~8~~,~0~~,2~-,~4--~16~~,8 METHANE, volume-percent

Frouu 1.-lgnitibility Curve anrl Limits of Flam­mability for Mcthano-Air Mixtures at Atmospheric Pressure and 26° C.

ignition of methane-air mixtures (75). For example, n 0.2-millijoule (mj) spark is inade­quate to ignite even a stoichiometric mixture at atmospheric pressure and 26° C; a 1-mj spark can ignite m1xtureB containing between 6 and 11.5 volume-percent methane, etc. Such limit­mixture compositionB that depend on the igni­tion source Btrength may be ~efined t\S limits of ignitibility or more simply i~nitibility limits; they aroe thus indicative ol the igniting abilit.y of the energy source. Limit mixtures that 11re C.'l..<~entially independent of the ignition source strength nnd t.hat give u. measure of the nbility of n tlnme to propugu.te uwt~y from the ignition source nmy he defined tls limitfl of flnmmtLbilit~·. Considerably gre11.ter stark energies nre required to estnblish lirni ts o flnmmalLilit.y than nre required for limits of ignitibility (218); further, more em•rgy is usually re<I,uired to estnblish the upper limit thnn is reqmred to estnblish tho lower limit. ! n gPnernl, when the source strength is udequnt.e, mixtures just. outside tlH' mnge of flnmmnble compositions yield flame ca~rs when ignited. These flume ctLps propagatP on .Y tL :,.;hort distancp from tlw ignition souretl in tt uniform rnixture. The r·etLson for this nlll,V he seell in figure 2 whirh shows the effect of tt•rnperntun• on limits of flamrnnhilit.y ut tL ('on,.;tnnt initial pressurl'. As the tmnpemtun• is iw·reusPd, t lw lowl'r limit dt•cronses and t.ltl'

IIPJWr limit ir:cn•u.ses. Thus, sitH'I· a lol'ali:wd Pnt'rg-,v sourt't. dt'\'ttiP~ the temperntur<' of IIP!ll'hy ~~!lSI'S, !'VI'Il ll lhlllflllllllllllhle mixtllft' ('1111

proprtgu t 11 lhmP a short distnm"(\ from t Itt>

DEFINITIONS AND THEORY 3

Upp41r limit

Flammable mixture a

(:::~ I I I

8 l rl'F::so~---=111:!·!_ ___ Lbw•r

limit I I I I

~ AIT TEMPERATURE--

F1ouu 2.--E.Ifect of Temperature on Limits of Flammabilit~· of a Combustible Vapor in Air at a Constant lmtial Pres~~ure.

source. That is, a nonflammable mixture (for example, composition-temperature point A, fig. 2) may hecqme flammable for a time, if its temperature is elevated sufficiently (composi­tion-temperature point B).

Flammable mixtur~ considered in figure 2 fall in one of t,hree regions. The first is left of the saturated vapor-air mixtures curve, in the region labf.'lled "Mist". Such mixtures consist. of droplets suspended in a vapor-air mixture; they are discussed in greater detsil in the section on formation of flammable mixtures. The second lies along the curve for saturated vapor-air mixtures; the last and most common regton lies to the right of this curve. Compositions in the second and third regions make up the saturated and unsaturated flammable mixtures of a combustible-oxidant system at a specified pressure.

In practice, complications may arise when flame propagation and flammability limit deter­minatiOns are made in small tubes. Since beat is transCerred to the tube wa.lis from the flame front by radiation, conduction, and convection, 11 flame may be quenched by the surroun.iing walls. Accordingly, limit determinations must be made in apparatus or such a size that. wall Qllenehing is minimized. A 2-inch-ID vertical tube is suit11ble for use with the paraffin hydrocarbons (methane, ethane, ete.) at at­mospheric pressure and room tempernture. However, surh a tube is neither ~ntisCartory under these eonditions Cor nuwy halo~enttted lind other <'ompounds nor Cor parnffin hydro­cnrbons nt \"ery low temperature:-~ 11nd pressures (1.97, £44}.

Be<·nuse of the many difficulties associated with ehoosing suitable apparatus, it is not surprising to find that the very existence of the

limits of flammability bas been questioned. After a thorough study, I...innett and Simpson concluded that while fundamental limits may exist there is no ex{>erimental evidence to indicate that such llimts have been measured (1Sf). In a more recent publication, Mullins reached the same concluston (154). Accord­ingly, the limits of tlammability obtained in an apparatus of suitable she and with a sat,is­factory ignition source should not be tenDed fundamental or absolu~ limits until the exist­ence of such limits bas been established. However, as long as experimentally determined limits are obtained under conditions similar to those found in practice, they may be used to design installations that are safe and to assess potential ~as-.explosion hazards.

lndustnally, heterogeneous single-phase (gas) and multi-phase (gas, liquid, and solid) flam-­mable mixtures are probably even more imp~r­tant than homogeneous gas mixtures. Un­fortunatel;v, our knowledre of such mixtures is rather !united. It is important to recogni?.e, however, that heterogeneous mixtures can ignite at concentrations that would normally be nonflammable if the mixture were homoge­neous. For example, 1 liter of methane can form a flammable mixture with air near the top of a 100-liter container, although a nonflam­mable (1.0 volume-percent) mixture would result if complete mixing occurred at room temperature. This is an importai!t concept, since layering can occur with any combustible gas or vapor in both stationary and flowing mixture..'!. Roberts, Pursall and Sellers (176-180) have presenteaan excellent series of review articles on the layering and dispersion of methane in coal mines.

The subject of flammable spra.vs, mists, and foams is well-documented (5, 18, ff, f7, 76, £05, 215, f45). Asain, where such hetero­geneous mixtures exiSt, flame propa.gat.ion can occur at so-called average concentrations well below the lower limit of flamml\bility (86); thus, the term "average" may be meaningless when used to define mixture composition in heterogeneous syst-ems.

IGNITION Lewis and von Elbe (180). Mullins (158, 154):

and Belle..'! nnd Swett (156) have prepa.re<l excellent reviews of the processes associated with spark-i~nition and spontaneous-ignition of 1\ flammable mixture. In general, many flammnhle mixtures can be ignited by sparks having a relatively small energy content (1 to 100 mj) but a large power density (greater t.han 1 megawatt/em8). However, when the source energy is diffuse, as in a sheet discha.r~e, even the totnl energy requirements for ignit10n

4 FLAMMABILIT'Y CHARACTERISTICS OF COMBUSTIBLE GASES AND VAPORS

may be extremely large (79, Bt, 85, 1$3, 181, 2$8). There is still much to be learned in this field, however, since electrical dischttrges are not normally as well defined in pra.ct.ice as they are in the laborator,Y.

When a. flammable miXture is heated to an elevated temperature, a. reaction is initiated ihat may proceed with sufficient rapidity to ignite the miXture. The time that elapses between the instant the mixture temperature is raised and that in which a flame appears is loosel,Y called the time lag or time delay before ignit1on. In general, tLis time delay decreo.ses as the t.em­perature increase.'i. According to Semenov (198), these quantities are related by the expression

0.22E log T=-r-+B, (3)

where T is the time delay before ignition in seconds; E is an apparent activation energy for the rate controlling reaction in calories per mole; Tis the absolute temperature, expressed in degrees, Kelvin; and B is a constant. Two types of ignition temperature data are found in the current literature. In the first, the effect of temperature on time delay is considered for de­lays of less than 1 second (127, 153). Such data are applicable to systems in which the contact time between the heated surface and a flowing flammable mixture is very short; they are not satisfactory when the contact time is indefinite. Further, equation (3) is o! little help, because it gives only the time delay for a range of tem­peratures at which a.ut.oignition occurs; if the temperature is reduced sufficiently, ignition does not occur. From the standpoint of safety, it is the lowest temperature at which ignition can occur that is of interest.. This is called the minimum spontaneous-ignition, or autoignition, temperature (AIT) and is dl!termined in a uni­formly heated apparatus that is sufficiently large to minimize wall quenching effects (194, 237). Figures 3 and 4 illustrate typical auto­ignition-temperature data. In figure 3 the minimum autoignition-temperature or AIT value for n-propyl nitrate is 170° C at an initial pressure of I ,000 psig (243). Data in this figure may be used to construct a log T

versus ~ plot such 11.8 that in figure 4. Such

graphs illustrate the applic:lbility of equation (3) to autoignition temperature dntn. The equation of the broken line in figure 4 is

log T= 12 ·~9_1()1 -25.1. (4)

In t.his specific case, equation (4) is applicable only in the temperature range from 170° t.o

195° C; another equation must be used for dt~ta at higher tempemtu.,res. The so!id lines in figure 4 define an 8 C band that mcludes the experimental points in the temperature range from 170° to 195° C.

FORMATION OF FLAMMABLE MIXTURES

In practice, heterogeneous mixtures are tllwa:vs formed when two gases or vapors are first "brou~ht toget.h~r. Be~ore dis?Wlsin.g tl~e fonnation of such m1xtures m detail, a snnph­fied mixer such as that shown in figure 5 will be considered briefly. This mixer consists of chambers 1 and 2 containing ~a.ses A a!1d JJ, respectively; chamber 2, whiCh contal~s a stirrer, is sepamte~ from chamber 1 and pls.ton 3 by a partition With a small holf', H. At tune tc, a force F applied to piston 3 drives gas A into chamber 2 at a constant rate. If gas A is distributed instantaneously throughout cham­ber 2 as soon a.s it pnsses through H, a compo­sition diagram such as that given in figure 6 results· the (uniform) piston motion starts at to and ~tops at t,.. However, if a time interval ~t is required to distribute a samll volume from chamber 1 throughout chamber 2, then .at any instant between to and t,. + At, a vanety of mixture compositions exists in cha~ber ~· This situation is represente~ schem~tlCally. m figure 7. The interval of t1me dunng wluch heterogeneous gas mixtures would exist. in the second case is determined in part by the rate at which gas A is added to chamber 2, b,r the size of the two chambers, and by the efficiency of the stirrer.

In practice, flammable mixtures may form either by accident, or design. When they are formed by accident, it is usually desirable to reduce the combustible co!lcentration quickly by udding enough air or inert gas to produce nonflammable mixtures. Under certam con­ditions, it may be possible to increase the com­bustible concentration so tls to produce a nonflammnble mixture. Such procedures !ire discussed in greater detail in the followmg section.

Flu.mnutble mixtures are encountered in production of many chemicals and in cert!tin physical operations. These include gnsfreem~ tl tank containing a combustible gas (2~2), drying plttstic-wire coating, and recovermg sofvent from n solvent-air mixture. Whe.n layering can oecur, as in drying operations, 1t is not enough to ttdd nir tlt such a rate that the overall mixture composition is below the ~ower limit of flnmmability (assuming that umform mixture.'! result). Special!rtwnutions must. be tuken to as."!ure the rupi formution of non­fliWlmable mixtures (235). When a batch

..

DEFINITIONS AND THEORY

.. g u I z 2240 .... z ~

"'20 a: 0 &&..

~

I • It

0 0

Sample vol,c:c

... 0.50 • 0.75 • 1.00 )( 1.50 D 1.75 0 2.00 0 2.25 6 2.50 v 2.75 • 3.00 • 3.25

ReQion of au toiQnitlon

FIGURE a.-Time DP.lay Before I~~:nition of NPN in Air at 1,000 Psi~~: ir. the Temperature Range From 150" to 210° C. (1-33 npparntus; typc-347, stainless steel test chamber.)

process is involved, an added precaution must be tukcn; u constituent at a pnrtittl pressw-e nettr its vupor pressure \'ulue nmy eondense when it is moment.urily compressed by addition of other gases or vapors. Accordingly, mix-

tures that are initially abova the UJ>per limit of flammability may become flammable. A simi­lar effect must be considered when mixtures are sampled with equipment that is cooler than the original sample; if vapor condenses in the

6 FLAMMABILITY CHARAcrERISTICS OF COMBUSTIBLE GASES AND VAPORS

TEMPERATURE, OC

210 200 190 180 170

400

en ~ 200 0 u G) en -~ .... z Reoion of ~

outoiQnition

"" 0:: 0 ~

"" m ~ ..J l&J • 0 • "" c :E .... • • 6V

to 0

RECIPROCAL

FroURB 4.-Logarithm of Time Delay Before Ignition of NPN in Air at 1,000 Palg Initial Pressure. (Data from figure 3.)

sampling line, the test sample will not yield accurate data. A flammable mixture sampled in this manner may appear to be nonflammable and thus create a hazardous situution (286).

A flammable mixture can a!so form at tem­perature.~ below the fla.sh point of the liquid combustible either i( the latter L'l spr!l~ed tnto the air, or if a mist or foam forms. With fine

mists and sprays (particle sizes below 10 mi­crons) the combustible concentration at the lower limit is about the same as that in uniform vapor-air mixtures (17, 18, 22, 24, 76, 245). However, 8.\; the droplet diameter increa.ses, the lower limit appears to decr~a.-.e. In studying this problem, Burgoyne found that coaJ'He drop-· lets tend to fall towards the flame front in an

..

DEFINITIONS AND THEORY 7

Chamber I Chamber 2

Figure 5.-Simplified mixer.

Fiouu 5.-Simplified Mixer.

. "': Ul

100~ ,,

ELAPSED TIME

FIGURE 6.-Com~osition of Gas in Chamber 2, Figure 5 (Instantaneous Mixing).

upward propagating flame, and as a result the concentration at the flame front actually ap­proaches the value found in lower limit mixtures

ELAPSED TIME

l I 1

FIGURE 7.-Compoeition of Gas in Chamber 2, Figure 5 (Delayed Mixing).

of fine droplets and vapors (14). With sprays, the motion of. the droplets also affects the limit composition, so that the resultant behavior is rather complex. The effect of !IWt and spray droplet size on the app_arent lower limit is illus­trated in figure 8. Kerosine vapor and mist data were obtained by Zabetakis and Rosen (145); tetralin mist data, by Burgoyne and Cohen (14); kerosine spray data, by Anson (5); and the methylene bistearamide data, by Browning, Tyler, and Krall (18).

Flammable mist-vapor-air mixtures may occur as the foam on a flammable liquid col­lapses. Thus, when ignited, many foams can propagate flame. Bartkowiak, Lambiris, and Za.betakis found that the pressure rue llP pro-

lOOr------------------------------------------------.

- - - - -- Stoichiometric cv 0: 80 mixture (decane-air) -:0 .06 .1: - tiO ~ ~ Kerosine spray 'i ;:, ... -.0 ·n; -&, E cv - .05 :a -~ 0 0 u ... 60 Kerosine vapor t; tiO cv

.<:: and mist ;:, ...

E .0 'ii .04 E

z 0 u 0 i=

.03 z

< 0 0:: __ Methylene

i 1-z bistearamide spray UJ (.) .02 .... z z

UJ 0 (.) (.)

-----~ / Tetralin mist z L_ Tetralin mist

~I .01 8

_..L_ ..L .:r:.-- 0 0 20 40 60 80 100 120 140 160

DROP~ .. ET DIAMETER, micron::;

FtOI'RE R.-VariatiOil in Lower Limits or Fllllllrnability of Various Combustibles iu Air ft.' a Function of Dro!Jiet Diameter.

•

8 FLAMMABILITY CHARACTERISTICS OF COMBUS'riBLE GASES AND VAPORS

duced in an enclosure by the eompletf:' combus­tion of a layer of foam of thickness h 1 is propor­tional to h1 and inversely proportional to h0 ,

the height of the air space above the liquid before foaming (7). That is

AP«.!!Y_· h4 (5)

Pre..~sures in excess of 30 psi were l?roduced by the ignition of foams in small contamers.

ThomalS found that an additional hazard could arise from production of foams by oxygen-

enriched air at reduced pressures (215). Air cam become oxygen-enriched as the pressure ito~ reduced, becn.use oxy!Xen is more soluble tluLil nitrogen in most liqmds (83). Thus the pres­ence of foams on combustible liquids nre a po­tential explosion hazard.

A flammable foa\m can also form on nonflam­mable liquid if the foam is genemted l>Y a flam­mable gas mixture instend of uir. Burgoyne and Steel, who studied this problem, found that the flnmmnbility of methnne-uir mixtures in water-bnse foums was ufTected by both the wet­ness of the fonm and the bubble size (28).

...

PRESENTATION OF DATA Limit-of-flammability data that have been

obtained o.t o. specified temperature and pressure with a particular combustible-oxidant-inert system may be presented on either a triangular or a rectan~ular plot. For example, figure 9 showH a tnangular flammability diagram for the system methane-oxygen-mtrogen. This method of presentation is frequently used because all mixture components are included in the diagram. However, as the sum of all mixture cornl?ositions at. any point on the tri­angular plot Is constant (100 pet,\ the diagram can be simplified by use of a rectangular plot (244). For examp1e, the flammable area of figure 9 may be presented as illustrated in figure 10. As noted, the oxygen concentration at any point is obtained by subtracting the methane and nitrogen concentrations at the point of interest from 100 as follows:

With either type of presentation, addition of methane, oxygen, or nitrogen to a particular mixture results in formation of a series of mix­tures that fall along the line between the com­position point (for example, Ml in figures 9 and 10) and the vertices of the bounding triangle. For example, addition of methane ( +CH.) to mixture M1 yields initially all mixture com­positions between M1 and C (100 pet CH4).

After a homogeneous mixture is produced, a new mixture composition point, such as M2, is obtained. Similarly, if oxygen is added ( +02)

to the mixture represented by point Ml, all compositions between M1 and 0 (100 pet 0 2)

are obtained initially; if nitrogen 1s added, all compositions between MI and N (100 pet N 2)

are obtained initially. If more than one gas is added to Ml, for example, methane and oxy­gen, the resultant CQmpusition point may be

Pet 0 2 = 100 pet-pet CH4-pct N2• (6) obtained by considering that the mixing process

'oa~o

FIGURE 9.--Flammability Diagram for the Ryatem Met.hane-Oxygen-Nitrogen at Atmoepb.erlo P..-ure and 26° C. 9

•

10 FLAMMABILITY CHARACTERISTICS OF COMBUSTIBLE GASES AND VAPORS

.. c • e • c;a- 60 • E :I 0 >

~::~::~;;~i::::I::~~a"~'i~c~alr£cit~~S:~~~~~N 20 40 60 100 NITROGEN, volume-percent

Frouu 10.-Flammability Diagram for the System Mcthan&-Oxygen-Nitrogen at Atmospheric Presa•arc and 26~ C. (Data from fig. 9).

occurs in two steps. First, the methane is added to Ml and the gases are mixed thoroughly to give M2. Oxygen is then added to M2 with mixing to give a new (flammable) mixture, M3. IC the methane and oxygen were added to u fixed volume at constant pressure, some of All and then of M2 would escape and mix with the surrounding atmosphere. In many instanees this is an importnnt ('OJisideration be!'nuse the resulting mixtures may be flamrnuhle. .For example, even if an inert gas is udded to a eonstant-volume tank tilled with rnetlumf>, flammuble mixtures <'tUI form outside the tnnk us the displu<'ed metlmne es!'npe,.; into the atmosphere. If the metharw is not dissipated quickly, u dangerous situutiori ctlll nrise.

When u mixture l'ompoueut is removed hv condensation or ubsorptwn, the corre.'lponding

composition point (for example, Ml in figures 9and 10) shift.'! away from the vertices C, 0, and N along the extensions to the lines MI-C, A/I -0 and Ml- N, indicated in figures 9 and 10 by the minus signs. The final composition is determined by the percentage of each component. removed from the initial mixture.

Mixtures with constant oxy~en-to-nitrogon ratio (as in air), are obt1Lined in figures 9 and 10 by joining the apex, C, with the appropriate mixture composition along the basehne, ON. 'J'hu!!, the Air line, CA, (fig. 10) is formed by joining C with the mixture A (21 percent 02 +79 percent N 2). Using this lnttor point, A, one ean readily determine the mixture composi­tions thnt are fonued wh~n mixture Ml i!'l displaced from an enclosure and mixed with air. Initially, all mixture compositions between M1

PRESENTATION OF DATA 11

and A would form. Since these wouid pass through the flammable mixture zone1 a hazard­ous condition would be created. Similarly, if pure combust.ible ca. were dumped into the atmosphere (air)1 all mixtures between C and A would form. Tnese would include the flam­mable mixtures alonff CA so that a hazardous condition would &g&lll be created, unless the c>mbustible were dissip&ted quickly.

Mixtures with constant ondant content are obtained by constructing straight lines paraillel to zero oxidant line· such mixtures also have a constant combustibie-plus-inert content. One particular constant oxidant line is of special lDlportance-the minimum constant oxidant line that is tangent to the flammability diagram or, in some cases, the one that passes through the extreme upper-limit-of-flammability value. This line gives the minimum oxidant (air, oxygen, chlorine, etc.) concentration needed to support combustion of a particular combustible at a specmed tempGrature and pressure. In 6~ures 9 and 10, the ta!lgent line gives the mmimlWl OXfgen value (Min 0 1, 12 volume­percent) requll'ed for flame propagation through methane-oxygen-nitrogen mixtures at 26° C and 1 atmosphere.

Another important construction line is that which gives the maximum nonflammable com­bustible-to-inert ratio (critical C/N). Mixtures along and below this line form nonflammable mixtures U{>On addition of oxidant. The critical C/N ratio JS the slope of the tangent line from the origin (Figs. 9 and 10), 100 percent oxidant, teO the lean side of the flammable mixtures curve. The reciprocal of this sloJ?e gives the minimum ratio of inert-to-combusttble at which nonflammable mixtures form upon addition of oxidant. It is of interest in fire extinguishing.

An increase in temperature or pressure usually widens the flammable range of a particular combustible-oxidant system. The effect of temperature is shown in figure 11; two flammable areas, T 1 and T1, are defined for a combustible-inert-oxidant system at constant pressure. The effect of f..tlmperature on the llli~ its of flammability of a combustible in a specified oxidant was previously shown in figure 2. This type of graph is especially useful since it gives the vapor pressure of the combustiblt~, the lower and upper temperature limits of flammability ( T1• and Tv), the flam­mable re¢on for a range of temperatures, and t.he autotgnition temperature (AlT). Nearly 20 of these graphs were presented by Van Dolah and coworkers for a group u( eom­bustibles used in flieht vehicles (t18).

The lower temperature limit, T~., is essentially the flash point of a combustible

1 in which up·

~ard propagation of flame is useQ; in general, it 1s somewhat lower than the flash point, in which

'r. air • 100 \- \ combuetible vapor-\ inert

Flammable midurtl

INERT, volume- percent -

Frouu 11.-Etrect of Initial Temperature on Limite of Flammability of a Combuetible Vapor--Inert-Air System at Atm01pherio Preeaure.

cr: 0 Q.

"' > 'It I Q. ~

9r---------------------·-------, " air • 100" - " J P4 vapor

u

0 200 800

INITIAL PRESSURE, mm HQ

Froua11: 12.-Etreot of Initial Preeaure on Limite of FlammabiUty of JP-4 (Jet Fuel Vapor) in Air at 26° c.

downward propagation of flame is used. Since T~. is the mtersection of thP lower-limit and vapor-pressure curves, a relationship can be developed between T~., or the flub point, and the constants defining the vapor pressure of a combustible liquid. An excellent summary: of such relatioiJShips hM befln presented by Mullins for simple fuels and fuel blends (164).

At l",onstant temperature, the flammable range of a combustible in a specified oxidant can be represented as in figure 12. Here the flam. mabie range of JP-4 vapor-air m.ixturee is given

•

12 FLAMMABILITY CHARACTERISTICS OF COMBUSTIBLE OASES AND VAPORS

Pvapor/P

Frouaz 13.-Eifect of Temperature and Pres~~ure on Limit11 of Flammability of a Combu11tible Vapor in a Specified Oxidant.

as a function of pressure (£41). A more generalized flammability diagram of a particular combustible-oxidant system can be presented in a three dimensional plot of temperature, pres­sure, a.nd combustible content-as illustrnted in figure 13 (£-'4). Here, composition is given as the ratio ol partial pressure of the cornbw;tible vapor, PvAP<>R, to the total pr~ure P. For lillY vAlue or P, the Jimit.'i of flammability arb given as a function of the temperature. For example, at 1 atmosphere (P = 1), the flammable range is bounded bv the lower limit curve L 1L,L,L4, and the upper limit curve U1 Ua; all mixtures alon~ the vapor pressure curve L4 U~' U, are ftamm~tble.

The flammable range is the same as that de­picted in figure 2. At constant temperature (for example, T1), the flammable range is bounded by the lower limit curve L 1Pu and the upper lim1t curve U1Put; the broken curve PL1Pu1 represent..'i the low pressure (quenched) limit. The flammable range is the same as that depicted in figure 12. A similar range is defined at temperatures T~, T 1 , and T4 which are less tht\n T1• However, at T1 and T4 the upper limit curves intersect the vapor pressure curves, so that. no upper limits are found above u; and u~. In other words, o.ll COII!Positions along U~U~' and U~~ are flamUlable. The curve

PRESENTATION OF DATA 13

1

"air= 100- !C aasolimt vapor- !C water vapor

70 100 120 140 150 160 170 180 190 200 210 212

Fwuu: l~l.-Flammability Diagram for the s,·stern Gasoline Yapor-Wnter Yapor-Air at 70° F (21° C) and at 212• F (1006 C) and At::1.uspheric Prt>esure.

L4P£U.U;U2 defines the range of limit mixtures which are satur!lted with fuel ntpor. Furtht>r, since L4 is the saturated lower limit mixture at one atmospht>re, T. is the flash point.

Sonae of the points considered in this and the pre' ious :,fiction are illustrated in figure 14 (282). This is the flammability diagram for the system gasoline vapor-Whll'r ntpor-air at 70° F (21° C) and 212° F (100 °C) and utmos­pherir pressure. The uir saturation tempera­ture, that is, the temperature at whirb satur1tted air contains the quantity of Wlltl'r giwn on the water Vllpor axis, is :\lso included. For vn•cise work, a much la~er gTaph or an enlnrgNnent of thl' region from 0 to 8 perrcnt gnsoline vapor and from 0 to :m percent wMer vapor would be used. However, figure 14 is ndequ1tte here. If water vnpor is added to a particular mixture ..t, all mixture rornpositions between ..t and purt> water vapor will form <ts notl'<l (if the temperature is at least 212° F), and the eorn­position point will shift towards the 100-

percent-water-vapor point. If water vapor is r~moved by eondensation or absorbtion, the composition point will move along the extension to the line drawn from A to the 100-percent­watt>r-vapor point. The same applies to the other t•omponents, air and gasoline, as indicated earlier. ~loreover, if more than one component is involved, the final composition point can be found by considering the effect. of each com­ponent separately.

Figure 14 is of special interest since it can be ust>d to evaluate the hazards associated with a ~as-freeing operation. .For example, mixture A represents n saturated gasoline vapor-air­water vapor mixture at 70° F. A more \·olatile gasoline than the one used here would give a saturated mixture with more gasoline vapor and less air in a closed tank~ a less volatile gasoline would give less gasoline vapor and more air. In any event, if a continuous supply of uir saturated with water vapor is added to a tank containing mi:'l:ture A, all compositions

•

14 FLAMMABILJT'/ CHARACTERISTICS OF COMBUSTIBJ,E GMIES AND VAPORS

between A and B (air plus water vapor) will be formed until all the ~asoline vapor is flushed !rom the tank, and mixtun B alotHl remuin~. If steam is used to flush mixture A from the tank, all compositions between A tmd 0 will form until e.ll the gasoline vapor bas been flushed from the tank and only steam remains (at 212° For higher). If the t:ank is permitted to cool, the steam will condense and air will be drawn into the tank ~ving mixtures along C-B. At 70" F, only arr plus a small amount of water vapor will remain.

If hot water and water vapor at 17 5° F are used to flush mixture A from the tank, the mixtur~ comiJosition can only shift along AO to E. Muctures between A and E that are flushed from the tank mix with air t,o give mixtures

between points along AE and B. Again, as the water vapor in t.best3 mixtures condens11'1 outside the tllnk, the co!uposition of the result­ant mixtures will shift awtty from the 100-percent-water-vapor point, 0. 'rbe mixture in the tank will remain at E unless air is used to flush the tank, in which ca..'!C mixture composi­tons between E and B will form. Again, if the water vapor within the tank condenses, the mixture c.omposition will shift away from C. In any event, at t.his temperature (17 5° F), the addition of air to mixture E will lead to forma­tion of flammable mixtures. Thus, mixture A cannot be flushed from a ta11k without for•-r.in~ flammable mixtures, 11nless steam or some other inert vapor or gas is used.

...

DEFLAGRATION AND DETONATION PROCESSES Onct> a flammable mixture is ignited, the

resulting flame, if not extinguildaed, will eitlat~r attach itseiC to the ignition source or propagate fram it. If it propagates from the !luurctl, tlw propagation rate will be either subsonic {de­flagration) or superoonic (detonation) relath-e to the unburned gu.s. IC it is sub~onic the pres­sure will equalize at t.he speed ol sound throuJ,Ch­uut the enclosure in which combm;tion is takmg place so that the pressure drop acroHH the flame (reaction) front will be relatively smn.ll. H the rate is supersonic, the rate of pressure equaliza­tion will be less than the propagation raw and thare will be an appreciable pressure drop aeross the flame front. Moreover, with most com­bmtible-air mixtures, at ordinary temperatureM, the ratio of the peak-to-initin.l pressure within the enclosure will seldom exceed about 8:1 in the former, but may be more than 40:1 in the latter l.'llse. The pressure buildup is especin.lly great when detonation follows a large pressure rise due to deftagration. The distance required for a deftagration to transit to a detonlltion depends on the flllmmable mixture, tempernture, p_I'_essure, the enclosure, and the ignition source. With a sufficiently powerful ignition sourbe, detonation may occur immediately upon igni­tion, even in the open. However, the ignition energy required to initiu.t3 a detonation is usun.lly many orders of magnitude greater than that required to initiate a deflagration (82, 24-9).

DEFLAGRATION Where a deflagration occurs in a s~hericn.l

enclosure of volume V with central ignitwn, the approxirn1tte pressure rise l:lP at IlL v instant t nfter ignition is given by the expres;-;ion..c;:

l:lP=KP S~ta <P IV - "'' {7)

and

{N)

where [(is n constnnt. Su is the hurning \'e)()(•ii-Y, 1', is the initi1Ll pre;;sure, /',. is th!' rnnxirnuin pre>~suro, T, is the initial temperuture, n1 is th(• nUI.nbM of moles of g-us iu the iuitinl mixtun•, tlh I>! the nu·nber of 111oles of g'tts in the hurrwd g-ns<';;, M, is the uvemge moleculut· wei1.d1t of the initi1J mixture, •\16 is tlw uveruge molt•culut·

wt~i~tht, nf t.lae burned gaaes, and TJ is the final (n.• · hlllk) tmnperature of the pro ucts. With otlitl' c:IC'loMUrM, or with non<'.entral ignition, the fltuue front iM diHturbed by the walls before l'lllllhustion is completed, so that ct\lculated preMsure etLnnot be t~xpected to approximate uctu.U prcmsure. Even with spherical encl011ures, t.lw flame front is not actually spherical, so that the wallA tend to disturb the flame before com­bustion iH complete (118, 130). A graph of the preHMure developed by the combustiOn of a stoichiometric methane-air mixture (central ignition) in 11 19.7 em diameter, 9-liter cylinder is given in figure 15. The calculated pressure for a 9-liter sphere is included for comparison; K in equation (7) was evaluated from the experimental curve at 70 milliseconds. The calculated curve follows the experimental curve closely about 75 milliseconds, when the latter curve has a break. This suggests that the flame front was affected by the cylinder walls in such a way that the rate of pressure rise decreased, and the experimental curve fell below the cn.lculated curve. Further, since the com­bustion gases were being cooled, the maximwn

IOOr------.------.------.,---~~ ~----- ----Pm

Calculated / ~ (9-liter sphere)--{

I 1 Experimental I (9-liter cylinder)

0 160 TIME, milliseconds

FJOHKE 15.---l'n'tll!urc Produced by Ignition of a !1.6 Volumn-l'crcent Methane-Air Mixture in 11 9-I.itPr ( :ylindt>r ( Expt•rimen tal).

16

16 FLAMMABILITY CHARACTERISTICS OF' COMBUSTIBLE OASES AND VAPORS

pressure fell below the calculated value. The minimum elapsed time (in milliseconds) re­quired to reach the maximum pressure appears to be about 75 W for the paraffin hydrocarbons and fuel blends such as gasoline; V is the volume in cubic feet in this case.

DETONATION

Wolfson and Dunn (51!, 1!30) have expressed the pressure ratio P2/P1 across a detonation front as

Pa ___ l_ ('Y M 2+ 1) (9) P,- 'Ys+ 1 1 1

'

where 'Ya is the specific he11.t ratio of the burned gases, 'YI is the_ s_pecific heat ratio of the initial mixture, and M 1 is the Mach nwnber of the detonation wave with respect to the initial mixture. M 1 is given in terms of the tempera­tures T and molecular weights W of t.he initial and final mixtures by the expression:

('YIMI2+1)1 ('Ya+l)2T2WI 'Y1~f12 - 'YaT,Wa

(10)

P,. (theoretical)

0

P,. (experimental i

E

2,000

Wolfson and Vunn have developed generalized cba.rts that simplify the operations involved in obtaining the pressure ratio as well as the den­sity and temperature/molecular weight ratios across the detonation wave and the energy release in the detonation wave.

Many investigators have measured and cal­culated detonation and reBooted pressures resulting from detonation waves (541 57, 1!04). Figure 16 from the data of Stoner aM Bleakney (204) gives the detonation vruocity, the static or detonation pressure, and the reflected pres­sure developed by a detonation wave propa­gating through hydrogen-oxygen mixtures at atmospheric pressure and 18° C.

BLAST PRESSURE

The pressures produced by a deflagration or a detonation are often sufficient to demolish an enclosure (reactor, building, etc.). As noted, a deflagration can produce pressure rises in excess of 8:1, and pressure rises of 40:1 (reflected pressure) can accompany a detonation. As ordinary structures can be demolished by pres­sure differentials of 2 or 3 psi, it is not surpnsing

45

40

35

30

P5 (experimental) 25 E ...

0

20 Q,~

15

10

5

I ,500 L-----'-----...1.---...L...-----'---·-L----....L-----l 0 20 30 40 50 GO 10 eo 90

H2 , volume- percent

FIGURII 16.-Detonatlon Velocity, V; Statio Preuure1 P,; and Reflected Prell8ure, P., Developed by a Detonation Wave Propagating Through Hydrogen-Oxygen !\U:a:turea in a Cylindrical Tttbe at Atmoephorlo Prtlllure and 18° c.

..

DE.FLAGRATION AND DETONATION PROCESSES 17 that even reinforced concrete structures have been completely demolished by explosions of near-limit flnmmable mixtures.

.Jacobs nnd coworkers hnve studied the dam­nge potential of detonation waves in great detail (91, 170). They hnve considered the principles involved in rupturing of pipes and vessels by detonations and the relevance of engineering and metalJurgical data to explosions. More recently, Randnll and Ginsburg (171) have in­vestigated bursting of tubular specimens at ordinary and reduced temperatures. They found that the detonation pressure required to burst such specimens was, in general, slightly higher than the corresponding static-bursting pressure. Ductility of the test specimen ap­peared to have little effect on the bursting pressure, but ductility increased the strength of pipes containing notches or other stress raisers.

When a detonation causes an enclosure to fail, u shock wave may propugate outward at a rute determined bv characteristics of the medium through wliich it is transmitted, and the twuilable energv. ll the shock velocity, V, is known, the resultin~ overpressure, (P-P,), is given by the expressiOn (20.1)

P-P.=P"[-y:?l][~-1} (11) where 'Y is the ratio of specific heuts, und a is the velocity of sound in the medium through which the shock wu ve passes. The upproximate dumugt~ potentiul cun be assessed from the dutu in table I (217).

In conducting experiments in which blast pressures mny be generated, special precautions

must be taken to protect the personnel and e9.uipment from blnst ttnd missiles. Browne, Hileman, and Weger (16) have reviewed the design criteria for suitnble barricndes. Other authors have considered the design of suitable lnboratories and structures to prevP.nt frag­ment damage to surrounding nr~9,s (44, 174, 203, 220).

TABLE I.-Conditions of failure of peak over­pressure-sensitive c!tments (217)

I Approx­imate

incident Structural element Failure blast

Glass windows, large and small.

Corrugat<Jd "~bestos ~iding.

Carr· Igak'<i st,eel or aluminurr: panel­ing.

Wood siding panel8, standard house construction.

Concrete or cinder­block wall panels, 8 or 12 inches thick (not. rein­forced).

Brick wall p1'1ncl, 8 or 12 inches thick (not reinforced).

over­pressure

(pei)

Usually shattering, 0. 5-1. 0 occasional frame failure.

Sh \ttering. 1. (}-2. 0

Connection failure, 1. (}-2. 0 followed by buck-lil•g.

Usually failure oc- 1. (}-2. 0 cure at main con-nectJons, allowing a whole panel to be i>lown in.

Shattering of the 2. (}-3. 0 wall.

Shearing and flexure I 7. o-s. 0 failures.

PREVE~VE MEASURES INERTING

In principle, a gas explosion hazard can be eliminated by removing either all flammable mixtures or all ignition sources ($3, !!40). Howeveri this is not always practical, as many industria operations require the or-esence of ftammable mixtures, and actual or potential ignition sources. Accordin~ly special pre­cautions must be taken to mirumize the damage that would result if an accidental ignition were to occur. One such precaution involves the use of explosive actuators which attempt to add inert. material at such a rate that an explosive reaction is quer.dwd before structural damage occurs (70, 7$). Figure 17 shows how the pressure varies with and without such protection. In the latter case, the pressure rise is approximately a cubic function of time, as noted earlier. In the former case, inert is add~d when the pressure or the rate of pressure rise exceeds a predetermined value. This occurs at the time t 1 in figure 17 when the exp!osiw~ actuators function to add the inert. As noted, the pressure increases momentarily abo,re the value found in the unprotected ca.se and then falls rapidly as tht~ combustion reaction is quenched by the inert.

FLAME ARRESTORS AND REUEF DIAPHRAGMS

Inert atmospheres must be used when not even a small explosive reaction can bv tolerated. However, when the ignition of tL flammable mixture would create little hazard if the burning mixture were vented, flame arrestors and relief diaphragms could be used effectively. The destgn of such systems is determined by the size and strength of the confining vessels, ducts, etc.

In recent studies of the efficiency of wire gauze and perforated block arrestors (161, 16!!), Palmer found the velocity of approach of the flame to be the major factor m determining whether fio.rne passed through an arrestor. For thflse two types of arrestors, he found the critical npproach velocity to be

and

18

V' = 1.75k(1~-To), mo.eQ/r. (12)

(13)

I w a:: ;:::) rn rn w a:: 0..

Unprotected

Protected

E~~PSED TIME --•

FrouaE 17.-Pressure Variation Following Ignition o( a Flammable l\lixtur<' in Unprotl•eted and Protl•cterl Enclosures.

where k is the thermal conductivity of the ~as; m is the mesh width; T11 is the men.n bulk tem­perature of the flame gases through the arrestor; To is the initial temperature of the arrestor; Q is the heat lost by unit area of flame; x. is the thickness of the flame propagating at the burn­in~ velocity, S; dis the diameter of an aperture; A is the area of a hole in unit area of the arrestor face; and t is the arrestor thickness.

Equations (12) and (13) can be used to determine the mesh width or aperture diam­eter needed to stop a flame having a particulnr approach velocity. In practice, application of these equations assumes a knowledge of the flame speed in the system of interest. Some useful data have been made available by Palmer and Rasbash and Rogowski (172, 178), as well as by Jost (118) and Lewis and von Elbe (130).

Tube bundles also may be used in place of wire scraens. S<.)tt found that these permit. increased aperture diametern for a given ap­proach velocity (19!!).

In practice, it may be desirable to install pressure relief vents· tv ~imit damage to duct systems where flc me may propaf~ate. Rasbash and Rogowski (173) found that with propane­and pentane-air mixtures, the maximum pres­sure PM (pounds per square inch) deveioJ?ed in an open-ended duct, havin(; a t•.ross sectiOn of 1 rt: is:

..

PREVENTIVE MEASURES 19

P.a~=0.07 ~· and 6=::; ~ ~48, (14)

where~ is the ratio of duct length to diameter.

However, the presence of an obstacle (bend, constriction, etc.) in the path of escaping gases increased the pressure due to resistance to fluid flow by the obstacle. Location of a relief vent near the ignition source decreased the maximum pressure as well as the flame speed. For values of K (cross-section area of duct/area of vent) greater than 1, th1138e authors found

0.8K5PM~l.BK, (15)

L where 25K532, and 6'5zf'530. To keep the

pressure at a minimum either many sme.ll vents or a continuous slot was recommended rather than a few large vents. In addition, vents should be located at positions where ignition is likely to occur and should open before the flame has traveled more than 2 feet.

When possible, relief vents should be used with flame arrestors. The vents tend not only to reduce the pressure W:thin a system following ignition but also to reductJ the flame speed, thus making all arrestors more effective. Un­fortunntel.v, in certain large applications (for example, drying ovens), it is d1fficult to use flame <trrestors effectively. In such cases, grenter relinnce nnst be placed on the proper funrtioning of relief vtmts. Simmonds and Cubbttge (42, 43, 195) huve ill\·est;~ltted the design of ..Jffeetiw• vents for industnul ovens. They found tw<> pettks in the pressure re,.ords obtttined during the V"nting of cubical ovens (fig. 18). The first peak, P 1; the oven volume, F; the fnctor, K; and the weight per unit urea (lb/ft2

) of relief, w, were relttted ns follows for '\ 25 penent town gas 3-air mixture:

/\~'lt3 =1.18kw+1.57. (16)

i\lore genemlly,

PI l' 113 =-oS.(0.3Kw+OA), (17)

where S. is the burning velocity of the mixture nt the m·en temperuture.

The first. pressure pulse WtlS nseribt>d to the rrlt'nse und motion of Lw relil'f Vl:'nt following i~uihm; the second pulse, to eontinul:'d .. mrn­ing ut nn inr·r·ettsed rute. '.!'he secor:d pulse represents th!'" pressure drop ncross the vent,

I Town 'f\.1\ rontalnr.l npprostmr.tf'ly A:.! J)r\ hydro~f'n, 17 pet rnrhon munoxldt•, J.~ pet nwthanto; ttw lmlaiiOP "a, .. ottwr hydrtJrurhons, 3 pet; nllrt>l(cn, v pet; carbon dlo•IU., :1 pel; and Ol)~en.

a:td it i.s thus proportional to K. ve.lues of Kit. was found that

Pa=K.

For small

(18)

As with ducts1 larger pressures Wicirf> obtained wheu obstructions were plll.(",ed in t.htl oven.

t

ELAPSED TIME--

FIGURE 18.--Pressure Produced by I~tlon of a l<'larnmablc Mixture in a Vented Oven.

In designing explosion reliefs for ovens, Sim­monds and Cubbage pointed out that (1) the reliefs should be cc...'lStru('ted :.n such a way that they do not form dangerous missiles if an explo­sion occurR; (2) the weight of the relief must be small so that it opens before the pressure builds up to a dnngerous level; (3) the areas and posi­tions of relief openings must be such that the explosion pressure is not excessive; (4) sufficient free spnce must be utilized around the oven to pl:lrmit sntisfactory operation of the relief and minimize risk of burns to personnel; and (5) oven doors should be fastened securely so that they do not open in the event of an explosion.

Burgovne and Wilson have presented the results ti'f an experimental study of pentane vapor-air exJ>losions in vessels of 60- and 200-cubic-foot volume (30). They found t,he rates of pressure rise grenter than could be predicted from l~tminar burning velocity data, so that the effect of 11. relief area in lowering the peak pressure was less than expected. All experi­ments were conducted at an initial pressure of 1 ~ttmosphere. Vent data for use at higher initiul pressues tlre summ~trized in nn nrticle bv Block (10); ll code for designing pressure relief systems htts been proposed in this article. Other authors httve considered the effects of temperature and characteristics of the flam­mable mixture on vent requirements (14, 35, 38, 45, 46, 134, 145, 168, 221).

FLAMMABILITY CHARAcrERISTICS The flammability data (limits of flamma­

bility, flash point, ignition temperature and burning veloctty) of t.he various chemical fll.m­ilies exhibit many similarities. Accordingly, the data presented here are grouped under the various commercially important families, blends, and miscellaneous combustibles.

PARAFFIN HYDROCARBONS (C,.H2n+2)

Limits in Air Lower and upper limits of flammability at

25° C (or at the temperature noted) and 1 atmosphere (£26 and U35) for many members of the paraffin hydrocarbon series are given in table 2, together with the molecular weight, M, vapor specific gravity, sp gr, stoichiometric composition in n.ir, 0,, (appendix B) and heat of combustion, ill. (183). At room tempera­ture and atmospheric or r~:~duccd pressure, the lower limits of flammability of most of this series fall in the range from 45 to 50 mg com-

bustible vapor per liter of air at standard con­ditions, that is, 0° C and 760 mm Hg (0.045 to 0.050 oz combustible vapor per cubic foot of air) (247). This is illustrated in figure 19 in which some lower limits of flammability are plotted against molecular weight; except for methane, ethane, and propane all limit values fall in a band between concentrations of approx­imately 45 and 50 mg/lr.

The following expre.~sion may be used to convert from a lower limit L in volume-percent of vapor in the vapor-air mixture to one in milligrams of combustible, per liter of air at standard conditions:

L (mg)= L (v_o!_pct) _, 1

[100-L (vol pct){sp vol ~g] (19)

specific volume being volume of combustible vapor per milligram of combustible. At stand­ard conditions (0° C and 760 mm Hg) this is about 22.414/l,OOOM, where M is the molecular

6r---~~----~-----r-----r----~----~------~----~----~----~

cr: ~ 0 ...J

0 I MOLECULAR WEIGHT, orams/mole

Frouam 19.-Ef!'ect of Molecular Weight on Lower Limits of Flammability of P!\raffin Hydrocarboll! at 25° C. 20

FLAMMABILITY CHARACTERISTICS 21

TABLE 2.-Properties of paraffin hydrocarbons

Lower 11mlt In air

Combuatlble M Formula Ref. (;::1 ...f:!. (~) Ref.

pet) c., 1

-------1-----1-------------------------------Methane................. CHo............. 16.04 Ethane.................. CoHo............ 30.111 Propane................. CaHa............ .W.llll n-Butane ................ CoH10........... 66.12 n-Pentane................ Coil.,........... 72. 16 n-Hexane ................. Coli,............ 88.17 n-Heptane. .. ............. c,H,._ .......... 100.20 n-Oetane ................. c,n,. ........... 114.23 n-Nonane. ............... Callao........... !28. 26 n-Deeane.. .............. Coolin........... 142.28 n· Undecane.............. CnH,............ 166.30 n-Do<lecnne.............. CuHn........... 170.33 n-Tridecane .............. Culln ........... 184.36 n-Tetradeeane. •....•.... c,.nao.... ....... 198.38 n-Pentadeeane ........... Cull11 ........... 212.41 n-Hexadecane.... .... .... Cull,............ 226. o&4

•t~.a·c. IIE63° c. •t-86' c.

Y:~ I 1.62 2. Ol 2.49 2. 98 3.46 3.94 4.43 4. 91 6. 40 6.88 6. 37 6.& 7. 33 7. 82

9.48 6.66 4.02 3.12 2.66 2.16 1.87 1.66 1.47 1.33 1.22 1.12 1.04 .97 .DO .&

weight of the combustible. Since L (vol pet) of most members of this series is much less than 100 percent, the lower limit can be expressed RS

L (~g)~o.45ML (vol pet). (20)

At any specified temperature, the ratio of the lower limit to the amount of combustible needed for complete combustion, 0,, also is approximately constant. This was first noted by Jones (95) and later by Lloyd (133), who found that for paraffin hydrocarbons at about 25° c,

(21)

For the complete combustion of the paraffin hydrocarbons, we have:

C,H2n+2+ (1.5n +0.5)02-nC02+ (n+ 1)Ha0,

so that in air {22)

100 C',= 1 +4. 773(1.5n+0.5) vol pet, (23)

where 4.773 is the reciprocal of 0.2095, the molar concentration of oxygen in dry air. The values of 0, (appendix B) are included in table 2. By weight tliese become

(',,= l,OOO[~Q_~+_l.008(2n+2JI mg, (24) 22.414X4.77:3(1.5n+0.5) 1

or

C =9 34 [14.03n+2.02J ~- (25) ,, . 1.5n+0.5 1

Thus, o,~87 mg/1, (26)

191.8 341.3 488.6 636.4 782.0 928.11

1076.8 1222.8 1369.7 1616.6 1663.6 1810.6 11167.4 2104.3 2261.2 2398.2

6.0 3.0 2.! 1. 8 1. 4 1. 2 1. 06 .06

•.& I. 76

1 .68

:gg I .liO .46 .43

0.68 .68 .62 .68 .66 .66 .66 .68 .68 .66 .66 .64 .68 .62 . 61 . 61

38 (.jOi 16. 0 1. 6 128 4/1) 41 (.jO 12. 4 2. 2 190 ~ 42 (III 11.6 2.4 210 48 (118 8.4 2.7 240 46 (.jO 7. 8 3. 1 270 • 47 fi-161 7. 4 3. 4 810 .jO

:~ =j~) 6.7 8.6 ----~- .... .. 49 t.m ............. . 48 (l.j6) I 6. 6 4. 2 380 ..... . 48 (~) -------- -------- ................ -----M 46 (1) ............................. .

~I m ::::::::,:::::::: :::::::: :::::: '" <'> ................ ········r···--

• Calculated value extrapolated to 26" C at BzplOIIVIIS Ree. Cmter, Federal Bureau of Mlllee.

Combining this equation with equation (21), we have

~6·(mg/1) ""'48 mg/1, (27)

for paraffin hydrocarbons, except methane, ethane, and propane. Substitution of this value into equation (20) gives

(28)

The following expression may be used to convert a lower limit value in volume-percent to a fuel-air (weight) ratio:

M [ L (vol pet) J L(F/A)=28.96 100-L (vol pet) . (29)

The reciprocal expression gives the air-fuel (weight) ratio:

28.96 [ 100 L(A/F>=-xr L (vol pet) (30)

As noted, the lower limits given in figure 19 were determined at room temperature and at­mospheric or reduced pressure. Lower limits vary with temperature as shown for methane in figure 20. The limit values obtained with up­ward propagation of flame ($1) fall fairly close to a straight line that passes through the lower limit value at 25° C and the flame temperature (1 225° C). This is in accordance with the White criterien that the flame temperature is constant at the lower limit (ttt). The data obtained by White with downward propagation of flame fall along a line parallel to the line through the limit values obtained with upward propagation. Taking the value 1,300° C as

22 FLAMMABILITY CHARACTERISTICS OF COMBUSTIBLE OASES AND VAPORS

5

Vapor pressure curve

% air= 100%-% methane

Flammable mixtures

Downward propagation of flame

Upward propagation of flame

0~----_.------~------~----~------~------~----~~----~ -200 0 200 400 600 800 1,000 1,200 1.400

TEMPERATURE, • C

Frouu 20.-Effect of Temperature on Lower Limit of Flr.mmability of Methane in Air at Atmospheric Pressure.

the approximate flame temperature for the paraffin hydrocarbon series (55), and using the lower limit values at room temperature in table 2, the limits of the first 10 paraffin hydrocar­bons are represented as in figures 21 and 22. Figure 21 _gives the lower limits in volume-per­cent and figure 22 in milligrams per liter. By weight, the lower limits of most members of this series again fall in a fairly narrow band ("higher hydrocarbons" region). Individual adiabatic flame temperatures can be determined lor lower limit mixtures using the data in table 2 and appendix C (55).

The straight lines of figures 21 and 22 are ~ven by:

L L L2&" ( 2 o ,= u• (1,300o·-25o) t- 5 ), (a I)

or L, -L =l-0.000784(t-25°). (32)

u•

They are described in more general terms by a

plot ol L,jL25• against the temperature (fig. 23, solid line) .

These data are also correlated fairly well with the modified Burgess-Wheeler Law suggested by Zabetakis, Lambiris, and Scott (242):

L,=L26·-~Ji. (t-25°), (:J3)

where t is the temperature in °C and flHc is the net heat of combu:stion in kilocalories per mole. Then,

LL, =1-L 0 · 7~TT (t-25°). (:34)

n• 2&··~.

Substituting the value I ,040 for Las·All. ob­tained by Spakowski (201), we have

LL, =l-0.000721(t-25°), (35)

2a•

which iR also given in figure 23 (or a limited temperature range with the broken line.

..

FLAMMABILITY CHARACTERISTICS 23

% air = 100%-% combustible

5

Flammable mixtures

0 200 400 600 800 1,000 1,200 1.400 TEMPERATURE, • C

FIGURE 21.-Effect of Temperature on Lower Limits of Flammabil!ty of 10 Paraffin Hydrocarbons in Air at Atmospheric Pressure.

Only the lower limit n.t 25° C and atmospheric pressure is needed to use figure 23. For exam­ple, assuming n. constttnt fltlme temperature, the ratio LJL26• ut 600° C is 0.55. The cnlculttted lower limit of methane nt 600° C therefore is 5.0X0.55, or 2.75 volume-percent. The sume value cnn be obtnined directly from figure 21. From the modified Burgess-WhAeler l..nw cur,·e, L,/L25.=0.585 at 600° C, so that Leoo·=2.92 volume-perrent.

l..imit-of-flammabilitv measurements are com­plicated by surface and vnpor-phtlse reactions that occur at temperatures abO\·e the uuto­ignition temperttture. For example, Burgoyne and Hirsch (25) have shown thnt metlumE>-air mixtures contnining Uf to 5 perrt>nl mrthane burn readily nt 1,000 <'. J.~xperimenls vn•re conducted with mixture~.-~ eontnining us lit ilf' us 0.5 percent metlume; figure 20 prt>dirts thnt u flame would not propngnte throu11:h surh n mixture.

Flammability experiments ut elevated tem­peratures indicl\te that in the absence of cool

flames (87, 88), the upper limit also increases linet1rly with temperature. The effect of tempernture appears to be fairly well correlated by the modified Burgess-Wheeler law:

If we assume that the heat release at the upper limit is equal to that at the lower limit, then

A plot of U,, Un• a~ainst temperature (fig. 24) Wlls used to compare recent experimental values of Rolin~son and coworkers (18£) (or methane­uir mixtures ut 15 psigwith those predicted h,Y the modified Burgess-Wheeler la.w. The experi­mental and calculated upper limits IU'e given in tnble 3 together with the difTerem·ei U,a~.­Uupor· In each CII.S(>, th('O difference is ~as than

24 FLAMMABILITY CHARACTERISTICS OF COMBUSTIBJ"E OASES .AND VAPORS

50 Higher hydro­

carbons

QL-----~------~----~------~----~------~----~--~--~ -200 0 200 400 600 800 1,000 1,200 1,400

TEMPERATURE, • C

FIGURE 22.-Effect of Temperature on Lower Limits of Flammability of lO Paraffin Hydrocarbons in Air at Atmospheric Pressure by Weight.

4 percent of the experimental value, which is approximately within the limit of experimental error. Earlier experiments of White (222) at temperatures to 400° C, with downward flame propagation, also are represented quite ade­quately by equation (37). For example, White found that the upper limit or pentane in llir (downward propagation) increased linearly from 4.50 volume-percent at about 17° C to 5.35 volume-percent at 300° C. The rntio of 5.35: 4.50 is 1.17, which compnres quite well with U.,.l.IUa.~·"" 1.20 obtained from figure 24.

Given the vapor pressure curve and the lower limit of ftammttbihty, the low .. temperature limit or approximate tlash point of a combustible can be calculated from either equation (32) or (35) (218). A pproxirnu te flash points were obtained previously, using onlY the \'llpor pressure curve and the lower limit nt ordinary or e)e,·ated temperatures (1.54). The vnlues obtained with this procedure ure somewhat low because the lower limit at any tempt>rature ~&bove the flash point is less than at the flash

point. The lower temperature limits of paraffin hydrocnrbon at atmospheric pressure are :_>;i,·en in table 4.

TABLE 3.-Upper flammability limits, U, of methane-air m·i:cturcs at 15 psig

TPrn~rature U.aprrl (VOl u .•.• (vol Uoale-UeapPr ( C) percent) perct>nt) (vol percent)

------25 •....••. _ 15. 5 15. 5 () 100 ________ 16. 3 16. 4 . I 200 .... - ... 17. () 17. 5 .s 300 ...... --. 17. !I 18. 6 .7

I (/811.

:\foderate changes in pressure do not ordi­narily nffE'Ct the limits of flammability of the pnruffins in nir, ns shown in figure 25 for pen­tane, hexane, and heptane in air (241) 111 u range from 75 to 760 mm Hg. The lower limit~;

...

FLAMMABILI1'Y CHARACTERISTICS

TABLE 4.-LoWt'r temperature lim·ils and auloignition tempera.rures of poraflin hydrocarbons at atmospheric prtsS'Ure ·

~let ha!le. __ ..... _ ..... ___ Ethane_ - ...• _., .. __ . _. __ Propane .•. ______________ n -Butane _______ . _____ . __ Isobutnne. _. __ ... _ n-Pentnne ..•.•... ________ r

II -Hezane _______________

n- Heptnne ___ . ___ .. ____ .. _ -Octane __ - _ .. _____ - -- .. -Nonane ________________ -Decnne _____ ... __ .. __ . _ -Dodectme ____ . _____ . ___

n n n n n - Hexndecane __ •• ________

1 Caculated value.

. 4

.2

0

Autoignition temperature Lower temper~~oture limit -In air

In i>ir In ozygen

·c

-187 -130 -102 -72 -·81 I -48 -26 I

-4 13 31 46 74

126

200

I "F ~lef. ·c "F Ref. ·c

-----305 (i) 537 999 ( 168) ---------202 {l) 515 959 (197)1 506 -152 (•) 466 871 (t 58) . --------96 (1) 405 761 (l.i7) 283

-114 I (I) 462 864 (158) 319 -54 (1) 258 496 (194) 258 -15 (159) 223 433 (19.$) 225

25 (16.9) 223 433 (B87) 20<1 56 (169) 220 428 (I.-J7) 208 88 (169) 206 40a (B.i7) --------

115 (169) 208 406 (187) 202 165

I (159) 204 399 (187) --------

259 (1) 205 401 (197) ----·---

~

~~Modified Burgess-Wheeler Low ~ ~ ~ .....

"F

--------943

-------·· 542 606 496 437 408 406

...................... 396

----------------

400 600 800 1,000 1,200

TEMPERATURE, °C

I Ref.

-··------(94)

··~ _ ... _ .. _-(191) (9-')

(144) (94) (,Q4)

(191) -----·--

(94) --- .............. -----·--

1,400

Frouu 23.-Efteet <>f Temperature on L,/L.,.• Ratio of Paraffin Hydrocarbons in Air at Atmoepheric Pressure.

26 FLAMMABILITY CHARACTERISTICS OF' COMBUSTIBLE GASES AND VAPORS

~ ~ ~

1.4 -----,- --- --,----r---·-.---l I

1.3 ·-

1.2

l.l

I.CJo ... -'--~~oo=---Too--3t;o---,.J400:-:----:-:3oo TEMPERATURE. • C

F'JOURE 24.-Effcct of Temperature on u.;u~· Ratio of Paraffin Hy<iro~arbons in Air at .~tmosphcric Pressure in t.htl AbJSencc of Cool Flames.

eoincide, but the upper limits, by weight, increase with incrensing moleculnr weight.

Bl volume, nt atmospheric. pressure and 25° C, Sptlkowski (201) found thnt the upper nnd low£'r limits were reltd.ed by the exprt'ssion:

(38)

However, the data presented h~re ure correlated ~ore precisely by a somewhat. simpler expres­siOn:

(39)

Neither expression i.·:~ applicable when cool flames are obtained. Substitution of equation (21) for Lu,. into equation (39) gives

U350 =4.8 .JO:,. (40)

The limits of flammability of natural gas (85-95 pet methane nnd 1.5-5 pet ethane) have been detenuined over tm extended pres­sure rnnge by ,Jones nnd coworkers (78, 106). They are given in figure 26 for pressures from 1 to 680 1\tmospheres (10,000 psig). An anu.lysis of these dnta shows the hmits vnry linea.rly with the log11rithm of the initial pressure. That is,

L (vol pct)=4.9-0.71 log P (a.tm), (41)

and

u (vol pet)=14.1+20.4 log r (atm), (42)

with a Rtn.ndnrd error of estimate of 0.53 vol pet for L nnd 1.51 vol pet for U.

Although the limits of flammnbility are not nffeeted signifieuntly by moderttte changes in pressure, the ternpemture limits are pressure dependent. As the tolttl pressure is lowered, the partin! pressure of the combustible must also be lowered to maintain n constant com­bustible eoncentru.tion. The effeet of pressure on the lower t.empemture limit of the normal pttrnffius pentane, hexane, heptane, and octane in air, for pressures from 0.2 to 2 atmospheres,

Heptane z 0

~ 300 a:: f-

ffi .::

I ::::: ' ~r---1 )------~---~ Pentane uro

z-o~ (.)""" I.LIIll)

~E f= en ::1 aJ ~ 0 (.)

100

~ ~ 0 100 200

Flammable mixtures

Cl:XJ ~

I I I 300 400 500 600 700 800

INITIAL PRESSURE, rnm Hg

Fwuu: 25.-Effcct of Prc811ure on Limite of Flammability of Pentape, Hexane, and Heptane in Air llt 26° C.

..

FLAMMABILITY CHARACTERISTICS

60.-----.-~---o-----r-----.,-----r·----~----~----~

% air = 100%-% natural gas

Flammable mixtures

10

o· 100 200 400 600 700 800 INITIAL PRESSURE, atmospheres

FwunE 26.-EifPI't of Pressure ou Limits of Flammability of Natural Gas in Air at 28° C.

is shown in figure 2i. The temperature limits WN'e euleuluted from the L 26 , vulues, the \'llpor prt'ssure t·un•es, und the dutu of figure 23.

Limits in Other Atmospheres

Limits of tlummubility of some pntnffin hy­droeurbons hn \'fl been determined in oxygen, l'blorirH', und oxides of nitrogen, a~· w£'11 us in rnixt urt•s of uir and ntrious irwrts. ThP lower limits in oxygt•n 1111d in 11 widP \'lll'it'IY of oxygPII-nitrogt•n mixturPs un' ('Sst•ntirdly the sallH' 11:- tho,.;p in uir ut th<• S!llll(' lt'lllflt'raltrr(• and presstrn• (fig. 10). Limit -oi-flurnrrrabilit v lllt'llSlll'Pillrllls b\' Bartkowiak und Zuht>tukl.~ for lllPt.hurw und PthurH' in l'ldorirll' ut I, i.S, u~HI 14.{) utrrwsphN·~s, I'Hil!-!'illg froru :.!!i" to 200° < , un• ''llllllllurrzPd Ill tuhl<•;o; !i and ti (8).

( 'em nrd und .Jorw,.; (-iiJ) hu \'t' prPst•nll·d gmphil'ally tlw limits of flrlllllllllbilityof till' fir·st ;-;ix llll'llllll'r-; of t ht> purnl!in ,.;prit•s in uir con­t uining- vurious irH'rts, bust•d on u l'l'(>l'l':il'lltn­t ron found ust•ful in sollll' ruining- upplicut ions und tr'l'!Liiug iul'rt gas or vupor as purt uf the

TABLE 5.-Limits offlam.mahih"ty of methane in chlcrine

Prt'!!Hnl'C, psig

Lirn:ts

----···-----Temperaturt•, ° C

--------.,.----100 200

------- ___ .. __ ------------

ut mosphPre with which the combustible is mixPtl. Till' ('nmpo:;it ion of u point on such u diugrnrrr, PXCPpt onP thut rt'prt'sPnts only com­bustiblt> nnd air, ennnot be rend d1reetly. ln~lt·ud, on(' must dt•trrrnine Ute compo!<ition of thP utrrrospherP, ndd tlw <'ombustiblP eon­tent, nnd then compute the total mixture com-

28 FLAMMABILI'fY Cl-L\HACTERI~TICS OF COMBUS7'IBI.E OASES AND VAPORS

40~

20L (,)

•

0.4 0.6 1 2 PRESSURE, atmospheres

F'IGURE 27.-Effect of Pressure on Lower Temperature Limits of Flammability of Pentane, llcxl\ne, Heptane, and Octane in Air.

TABLE 6.-Limits of flammability of Fthane w ch~orine

(volumo-perC('nt)

Pressure, psig

Limits Temperature, 0

('

25 100 200 -----·-----·-------------(} ____________ {Lower .. ..

Lpper .. .. 100 ...... _ .. _{Lower ... .

Upper .. .. 200 __________ {b~;~~~::: --liil'" '"7:i"

6. 1 2. 5 58 58

3. 5 I. 0 03 75

2. 5

1.0 112

76

position. This iu~s been done for met l11tne through hexane (fig~. 2S-a:l). ( ~ompo~ition~ 1~re determined directly fmm the ub~ri~su~ (inert conrentmtion) and onlinut.es (combustible Coll­centration); tlw nir iu nny mixture is t hr diffrr­ence between 100 l'frcrnt. and the sum of inert und eombu:-3tible. Datu of Burgoyne nnd Willitun~>· Leh· for· met.lume-methyl l>l'omide (l\1 eBr) -uir ar:d rn<>t lmne-cnrbon tPtm<'hloridt'­'tir mixture~:~ are included in figure 2S (2!J).

Unfortunat.ely, the methane-methyl bromide­air data were obtained in a 1 %-inch tube. Although satlsfa.ct.,ry for methan~ and other hydrocarbonP., thL~ tube is apparently not sa.t1sfactory {or many of the lmlogenated hydro­carbons. Thw~ n recent induHtrial exj)losion involvio~ methyi bromide prompted Hill to reconsider the fla•mmability of methyl bromide ht air (84). He found that. m«~thyl bromide was not. , .nly ilammable in air but that. it ful'med flammable mixtures •\t I a.tmospberl' wit~ a wider variety o( l'Oil(~entratiom1 than Jones had reportJd (96). This would sug~~~~- that there is no justification Cor ! be as!•Ulltption that Jones' flammabiW .r data for methyl bromidP. were influenced by the presence of mcrcur.Y vapor (196). Hill's limit vulues tLt utmosphertc pressure nr<'- included in figur{l 28 and arc used to futm the approximate, broken, fiammabilitr curves for the methane-methy' bromide-a1r system.

Data of Moran and Bertschy for pentane­perfluoropropane-air, pentane-sulfur hexafluo­ride-air and penta.ne-perfluoromethane-air mix­tures are included in figure 32 (14-'i'). Data by Burgoyne and Williams-I..eir for hexR.ne-methyl bromide-air and hexo.ne-Frflon-12 4 (F -12; Cli"'2Cl2)-air mixtures have been included in figure 33. 'rhese dt~.ta were all obtained in r%-inch-diameter tubes. An investigation of flv.mm•1bility of hexane-methyl bromide-air mixtures in a 4-inch tube indictlted that an in­crease in tube size (from 1 %-inches to 4-inehes­ID) resulted in a narrowing of the flammable range; the upper limit decreased from 7.5 to 5.7 volume-percent n-hexane VtLpor in air while the lower limit remained constant. The amount of methyl bromide required for extinc­tion decreased from 7.05 volume-percent in the 1 }Hnch tube to 6.0 volume-percent m the 4-inch tube. However, agnin this is not in line with the result:;; obtained by Hill with methyl bromide-air mixtures (84). Accordingly, while the dnta obtained in tlpproximtttely 2-inch tubes were used to construct figure 33, the Hill dt~ta, obtttined in •t larger .~ppnratus, •tre nlso used to form the approxinu~t(', broken, flnmmtthility curves for the hexane-methyl bromide-air system.

The limits of flammn.bility dia!tfams for the syst.em n-heptune-\•ater Vttpor-air n t 100° nnd 200° C (fig. 34) show the effects of tempernture on u system that, prvrluces both normal unrl eool fhmes t~t ntr.wspheric pres1-mre (W2). In­teresting!;' enough, the nunimum oxygen re­quirement for flume propugtttion (:\tin 02) ut 200v C is the snme for the eool llllrl m•rmnl tlt~rne regions in this instnnce. Further, the decrense in :'1inimum oxygen requirements

• Trade names are used (or lll~nttncatlon 11nly; this doo• not tmply endoraement hy the Bureau or N.'.tnes.

..

FLAMMABIL.ITY CH.Al' ~C'l'ERISTICS 29

. I

%air= 100%--;,; methane-% inert

12

4 \ \ \ \ \ \

' \ 2 \ \ \ \ \ \ \ "- \ 0 10 20 30 40 50

ADDED INERT, volume-percent

FIUUIU: 28.~-Limits of Flammability of Various Mcthanc.Iner. ·,s-Air Mixtures at 25° C alld Atmospheric Pressure.

(from l:l.5±0.3 volume-percent, tlt 100° C to 12.8±0.:3 volume-pen·ent at. 200° C) is wit' in the rnn~e predi(•t.ed by the modified Hurgess­\\'lu•eler ltlW (equntion a;, nnd fi~. 2:~). How­ever, the n vnilnble dn t.n 1: "C too nu~n~:·:-r nt present to permit n ren.listie <n-ahmtion ,,f the v t\iidi tv of this In w.

I IISJlectionof the limit-of-fltunnutbility eurves in figUI'es 2S to 33 reveuls thut c ·;cept for methuuc und Pthane, the minimum amounts of carbon dioxide and nitrogen required fo!" flame

extinction (peak values) at 25° C and atmos­pheric pressure nre about, 28 and 42 volume­prrcent., respectively. T;_ n~.tio of these values 1s npprm · · ;1\tely inverselr pr0portional to the mtio of theli 11ent capncittes at the temperature nt which <'t>.''bustiOn occurs. Al".cordingly, generalized flamm»bility diagrams of the type given in figure 35 can be constructed for the higher hyd" "t\rbons, ignoring the presence of cool flames. 3uch diagrams do not appear to be applicable to the halogenated hydrocarbons

30 FLAMMABILITY CHARACTERISTICS OF COMBUS'l'IBLE GASES AND VAPORS

%air= 100%-% ethane-% inert

-c Q)

~ !. 8 cV E Flammable :::J

mixtures ~

LLi z 6 < :I: !:;:;

4

0 10 20 30 40 50 ADDED INERT, volume-percent

Fu; :JRE 29.-Limits of Flammability of Ethane-Carbon Dioxide-Air and EthanP-~itrogen-Air Mixtures at 2.'i° C and Atmospheric Prl's!!ure.

since these materials tend to decompose even in flames of limit-mixture composition nnd, as noted, may themselves propugute flume. Cole­man (J7) hns found that the mtios of the peuk values of u halogenated hydrocnrbon ure not constant but ttre proportionul to the hents of combustion of the combustibles to which the halogenu ted h.vdrocarbon is added.

Few data are ttvniluble for the etfpets of pressure on the limits of flammability of eom­bustible-inert-air mixtures. One such set of data is summarized in figure 36, which gives the limits of flttmmability of nttturnl gas (85 pet methane+ 15 pet ethane) nitrogen-air at 26° C ttnd 0, 500, 1,000 and 2,000 psig (105).

Similnr dttttt nre given for ethnne-cnrbon dioxide-nir (fig. :~7) and Ptluuw-nitrogen-nir (fig. :~s) (121), IUHI fot· propnne-eurbon dioxide­nir (fig. a9) und propnne-nitrogen-nir (fig. 40) (122). Minimum oxygen requirements for flame propngtttion (min 0 2) through nntuml gns-ni trogen-uir, ethnne-ni trogen-nir, und prn­pane-nitrogen-nir at utmospheric nnd elevnted pressures nnd 26 ° Cum sumnutrized in figure 41. fhe minimum 0 2 vulues in volume-p:,rceut

11re reluted to pressure 11s follows: ·

for nuturnl gus:

Min. 0 2 = 13.98-1.68 log P; (4:$)

...

FLAMMABILITY CHARACTERISTICS 31

lOr-------~-------r------~------~.-----~

% air = 100%-% propane-% inert

-c:: Q) u ... Q) a. 6 ci.l Flammable E mixtures ::I 0 > t.J' z <C 4 Cl. 0 0:::: 0..

2

0 10 20 30 40 50 ADDED INERT, volume-percent

FIGURE 30.-Limits or Flammability or Propane-Carbon Dioxide-Air and Propane-Nitrogen-Air Mixtures at 25° c and Atmospheric Pl'essure.

for ethane:

Min. 02= 12.60-t.a6 log P; and (44)

for proptme:

Min. 0 2 =13.29-1.52 log P; (45)

where P is the initial pressure in pBia. The luwAr limit of flammability or any

mixture of the ptmtffin hydrocarbon~ can be calculated by Le Chatelier's law (40, 12iJ, 235):

100 " f.-~' -n--,' ') ~ ( 1

t = 100 (46) '5: (I 1:1 1=1 L.

where r. and L. are the percentagll comP.osition and lower limit, respectively, of the 1'b com­bustible in the mixture. For example, a

mixture containing 80 volume-percent methane, 15 volume-percent. ethane and 5 volume-percent propane Las a lower limit in air at 25° C and atmospheric preBSure of:

100 L2.10=so-t;s-5=4.a vol pet. (47)

-+-+-5.0 a.o 2.1

Liquid mixtures can be treated in the same way if the relative escaping tendencies of the various components are known. Since the paraffin hydrocarbons obey Raoult's law (143), the partial pressure or each component can be calculated a.s follows:

(48)

where p1 is the vapor pressure of the illl com-

32 FLAMMABILITY CHARACTERISTICS OF COMBUSTIBLE GASES AND VAPORS

10~--------~--------r-------~--------r-------~

% air = 100%-% butane-% inert

-c:

" ~ 6 " a. cb E Flammable :l

g mixtures LLJ

4 z ~ Cst :;) CD

2

0 10 20 30 40 50 ADDED INERT, volume-percent

FrouaJD 31.-Limits of Flammability of Butane-Carbon Dioxide-Air and Butane-Nitrogen-Air Mixtures at 25° C an:i Atm1.1spheric Pressure.

ponent in the blend, Po is the vapor pressure of the pure component and N, is its mole fraction in the solution. This procedure has been used to calculate the lower temperature limits of decane-dodecane blends in air (fig. 42). The vapor pressures of decane and dodecane and the calculated low temperature limits are given by solid lines and four experimental vo.lues by circles.

Autoignition

Two types <,f autoignition data are obtained depending upon whether the objective is to cause or to prevent the ignition of a combustible in air. The first type are usually obtained at high temperatures, where the ignition delay is relatively short. Typical of these u.re the data of Mullfus (159), Brokaw and Jackson (15, 90),

Ashman and Buchler (6), and Kuchta, Lam­biris, and Zabetakis (127). These are not normally used for safety purposes, unless there is some assurance that the contact time of combustible and air is less than the ignition delay at the temperature of the hot zone. The minimum autoignition temperature (AlT) is usually the quantity of interest in safety work, especially when combustible and air can remain in contact for an indefinite period.

Some Al'r values for paraflin hydrocarbons in air obtained by Setchkin in a !-liter spherical Pyrex flask (194) and by Zabetakis, Furno, and Jones in a 200 cc Pyrex Erlenmeyer flask (237) are given in table 4. Interestingly enough, experiments conducted in these and other flasks generally indicate that fla..-.k shape and size are important in determining the AlT. The AIT data obtained in the 200 ac flask may

..

FLAMMABILITY CHARACTERISTICS 33

8~----~-------~-----,-------r-----.

% air= 100%-% n-pentane-% inert

7

6

...... c C1)

~ 5 C1)

a. cb E -= 0 > 0: 4 0 a.. ~ LLJ z ~ 3 z LLJ a.. c:::

2

1

0 10 20 30 40 50 ADDED INERT, volume-percent

FIGURE 32.-Limits of Flammability of Various n-Pentane-Inert Gas-Air Mixtures at 25° C and Atmospheric Pressure.

34 FLA.l'dMABILlTY CHARACTERISTICS OF COMBUSTIBLE G.\BES AND VAPORS

... c:: Cl)

~ Cl) c. cb E :::l 0 > ~ 0 a.. < > UJ z

~ :I: c::

8r-------~------~------T--------r-----~

7

6

5

4

3

2

1

0

\

' '

% air = 100%-% n-hexane-% inert

MeBr

' 10 20 30 40 50

ADDED INERT, volume-percent

FwuRE 33.-Limits of Flnmmnbility of Various n-lll•xnnc-lncrt Gns-Air :\lixtures nt 25° C lllHI Atmospheric Prc88urc.

..

FLAMMABILITY CHARACTERISTICS 35

FtOURE 34.-LirnitR of Flammability of n-ll<'ptan(•-Wnt!'r Ynpor-Air :\lixturcs at 100° and 200° C and Atmospheric Prct~~~urc.

36 FLAMMABILITY CHARACTJo:RISTICS OF COMBUSTIBLE GASES AND VAPORS

4r-------~------~~-------~------·~--------

L

0

% air = 100%-% combustible-% inert

Flammable mixtures

10 20 30 40 ADDED INERT, volume-percent

50

FIGURE 35.-Approximate Limits or Flammability or Higher Paraffin Hydrocarbons (C.Hso+J• n ~5) in Carbon Dio:~ide-Air and Nitrogen-Air Mixtures at 25° C and Atmospheric Pre88ure.

FLAMMABILITY CHARACTERISTICS

~~~--~------~~"

8

0

%air= 100%-% nitrogen-% natural gas

Flammable mixtures

8 16 24

1,000 psig

32 40 48 ADDED NITROGEN, volume-percent

56 64

FI<·t:RE 36.-Effect of Pressure on Limits of Flammability of ~atural Gas..~itrogen-Air Mixtures at 26° C.

37

38 FLA~I.MADILITY CHAR.,CTF:HIHTICfl OF COMBUISTIBLE OASES AND VAPORS

%air= 100%-% ethane-% C02

40 -s:::: Q) 0 .... Q) 0. 32 cV E :l 0 > u..i 24 z < :I: 1-LLJ

16

CARBON DIOXIDE, volume-percent

Fl<..l"kt: :!7.-Eff,.et of Pn·s~oir<· 011 Liruit .. ot l'lnrnmnhility uf Ethallt•.('arholl ))joxido·-Air :\li~.tur•·• ar :.!t\ · I·

•

..

F'LAMMABII.ITY CHARACTERISTICS 39

... c::: Q) u .... Q)

32 0. ci> E ;:::)

0 >

24 w z <( J: 1-LLJ 16

0 8 16 24 32 40 48 56 ADDED NITROGEN. volume-percent

FJUI'RJ: :\'<.- LIL·;·t of l'n·~,;ur•• on Limits of Fl:tmmability of Ethtlllt'-:'\itrog••n-Air :\fixtures at 26° C.

40 FLAM_11;!ABILITY CHARACTERISTICS OF COMDUSTIIH .. f; GASES AND VAPORS

40~-------~------·~------~--

-c: QJ

~

32

QJ

a. 24 -cil E ::l

~ LJ..i z Cf 16 0 a:: a..

8

0

% air= 100%-% propane-% C02

~200 psig

Atmospheric

B 1b 24 32 CARBON DIOXIDE, volume-percent

40

FIGURE 3H.-Eifect of Prcssu:c on Limits of Flammability of Propane-Carbon Dioxide-Air l\fixtureR.

48

..

FLAMMABILITY CHARACTERISTICS 41

4U ---r-% air= 100%-% propane-% N2

32

-c:: Q) u ... Q) c.

24 cil E :::s 0 :>

L..l,j z

16 ca: ll.. 0 0:: ll..

Atmospheric

8

0 8 16 24 32 40 48 56 ADDED NITROGEN, volume-percent

FIGURE 40.-Effect of Pressure on Limits of Flammability of Propane-Nitrogen-Air Mixtures.

be correlated with molecular structure by plotting them against the nverage carbon chain length defined 8.'1

II 2:;:; g,N,

L • .,=M(M_:_I )' (49)

where g, is the number of possible chnins each c·ontnining N 1 etlrbon atoms nnd ,\/ is the nm:t­her of methyl {---( '11 3 ) groups. For example, n-nontme und 2,2,:J,'J-tetramethyl pent tine each have !l carbon nt01ns, hut the former has 2 methyl groups tmd the lntter hu' li. The former hns only one dtuin of !l l'nrbou atoms with n methyl ·group on ench end, und the lntter h11s ll IOII.Xillllllll of 4 dmins With a l'llrhon Ill oms, S dtnins with 4 c~urhon l!loms, und :l dtnins with 5 e~trhou ut mns. Thus, 11-liOilllllC hns an 11 veruge rhuin l••ngth of ' und 2,2,:!,:\-tetnunethvl

Ilenlnlll' hn..; 1t11 n vernge oi :Ul. The more highly muwlwd " c•omhustihh1 is, I h~ higher its

ignition ll'mpemture will bt>. .\linirnmu unto­ignition temperutures of 20 pnraflin~ were plotted lUI ordinate against the average chnin

length as abscissa (fig. 43). The data fall into two regions-a high-temperature region in which the AIT is greater than 400° C and a. low temperature region in which the AI T is less t.han 300° C. These regions coincide with those of Mulcahy who found that oxidation proceeds by one of two different mechanisms (162}, aud by Frank, Blackham, and Swarts (60). The AIT values of combustibles in the first region are normally much more sensitive to the oxy­gen con<~entmtion of the oxidizing atmosphere and to the spray injection pressure than are the c·omhust ible.'> in the second region. Unfortu­nately, the avuilable consistent AIT data about the effec's of oxygen concentration and in­jection pressure are too meager to permit a det~tiled compurison.

The physical processes (206) ano reactions thnt lead 'to aut.uignition are of interest in any detailed study of this ignitinn process. Salooja. {18-D, Terao (20'7), Affens, ,Johnson and Carhart (1, 2), and others have ~>tudi('d the aut.oignition of vnriom; hydrocarbons in an effort to deter­mine the mechanisms that lead to the ignition reaction.

42 FLAMMABILITY CHARACTERISTICS OF COMBUSTIBLE GASES AND VAPORS

2,000

1,000 800

600

IV 400 "iii c. uJ 0:: ::J en 200 en LLJ 0::: c..

100 80

60

40

20

10~------~------~------~------~ 6 8 10 12 14

OXYGEN, volume-percent

FIGtr!IE 41.--Effcct of Pressure on Minimum Oxygen Requir!'ffit'nts for Flume Propagutiou Through ~ntural Gus­Nitrogcu-Air, Ethune-:\'itro!(Pll-Air, uud l'rop111H'-:..;itrop;m-Air :\lixtun·s at 26° C.

An increase in pressure !!Pilerally deC'renses the AIT of a combustible in It givrn oxidunt. For exumple, the AIT of n llntuml gas in nir deerrused fmm 5:W 0

(' ttl I nt mospiH•rt> to 240° (' nt tiiO atmospheres (V,OOO p,.;ig) (78). Tlw AIT's of seveml hydroetlrbons were found to oht•y Semenov 's tHpiution over ulimited pre;:sure range (24H):

(.'iO)

where Tis the AJT nt ttn initinl {>ressure P, ttnd A nnd lJ ttl"e constunts. Aeeor< ingly, the AIT vnlm•,.; ohtnined at at mospherie pn~,.;sme should not he used to ass<•ss i!!nition ha:mrds ut high pressures.

Burning Rate

The burning velocities, Su, of various hydro­carbons hav<• been mensured by numerous in­vestigator;: in nir und other oxidnnts (68, 131). At one n.tmosphere and 26° C, the burning

...

FLAMMABILITY CHARA~ERISTICS

TEMPERATURE, o F

32 68 104 140 176 212 248

-c:: OJ u ....

1.32 OJ 0.

1.05 cb

.79 E ~

w 0 .53 >

0:: ~ ::::::1

en .39 0 en ~ UJ <t 0:: .26 > ~ UJ 0::: .....1

0 co ~ 1 .13 i= oes: en > => co

:E 0 u

0 20 40 60 80 100 120 TEMPERATURE, o C

FiauaE 42.·-Low-Temperature Limit of Flammability of Decane-Air, Dodecane-Air and Decane-Dodecane-Air Mixtures (Experimental Points 0).

velocities of paraffin hydrocarbons in air range from a few centimeters a second near the limits to about 45 cmjse<~ near the stoichiometric mixture compm1ition; much higher values 11.re obtained with paraffin hydrocarbon-oxygen mix­tures. Figurt3 44 gives results obtained by Gabbs and Calcote for four paraffin hydrocar­bon-air mixtures at atmospheric. pressure and room iemperature (GB). The d~ttn are mr­pressed in Umns of the stoichiometric composi­Jion. C.,; burning veloeities are given for the <'omposition rnnge fro111 0.'1 to 1.4 (', 1• These nut hors hnve presented similnr dnt n for eom­bustible.-, Ill 25° and 100° ( '. Figure 45 gives results oht~tined by Sin~er, Urumer, tuH.l Cook for three pamffin hydroe~trbon-oxvgen mixlme." nt ntrnosplwrie (He."\sure nnd r·oori1 tempernt ure in the mnge from 0.:~ to I .4 0, (J.f/8). Burning vekeities runge from !l low of l2.'i em/see to 11 high of 4:l,i cmjsc•t'; t he,..;e vnlue,.; nrt• <'onsidt•r­uhl,v ~rcutrr tluu, thost• ohtninrd in nir. A <·hunge in t>ither tempemture or J>I"P,;,;un• will ultt•r S" for n pnrt icultu· mixture. For l'Xtllll piP,

Ag-new tllld nruiff (8) found t hnt till irH'I'l\11'-l' in pres.~un• <'tlll,...es 8. of stoichiPIIletrir mc·tlume-nir 1111d proptuw-uir mixtures to decrense in the pr,•.;surP mngc from O . .'i to 20 ntmospht'l"l\'i (fi~. 4(i); S, of ;.toiehiometric metlmrH•-oxygcn mix­tures, iwwover, increa..'lcd in the pr<ossure ru.ngt~

from 0.2 to 2 atmospheres (fig. 47). The effect of temperature is more consistent. For a given pressure and mixture composition, an increase m tempera.ture raises s.. In general:

(51)

where A and Bare constants, Tis the tempera­ture nnd n is a constant for a particular mixture composition. Dugger, Heimel, and Weast (SO, .51, 81) obtained a value of 2.0 for n for some of the paraffin hydrocarbons (fig. 48). 'l'hc burning velocity of the stoichiometric methane-nir u.nd methane-oxygen mixtures given in figures 44 nnd 45 do not agree with the Vt\lues given in figures 4H to 48 but, in each case, the burning velocity dntn are internnlly consistent.

The nctunl tlt\me speed relative to a fixed observer mny be much gre11.t~r thnn S. since the hurrwd gtlses, if not vented, will expand und impllrt u mot ion to the flnme zone. If detonn-1 ion occurs, the r~lll'l ion speed inrrctt:.-es mnrk­edly. For exnmpl(', figur(' 40 gives tlw Kogarko dnta on veltwitie..; with whirh n detomttion Wtwe propagntes through vurious nwthtule~nir mix­tures nt utmosplwric pr·essure in n :W.5 em­diumetrr pipe (llli). ~imilnr r~ults htlve been ohtuinetl hv <lt•r·.,tl'in, ( 'ttrlson, nnd Hill 111. low pr('.-~sures with lltllllrlll ga:;-air mixtures (67).

44 FLAMMABILITY CHARACTERISTICS OF COMBUSTIBLE OASES AND VAPORS

(..) 0

uJ cc a:: C-C·C·C·C :::::> .... . . c( cc a:: L&J c 0..

C·C·C·C·C ::iE UJ c c .... z 0 .... z 350 (.!)

0 .... c :=» c( 6 ::iE C·C·C·C·C :=» 300 ::iE c z c ::E

n-CgH2o 250

AVERAGE CARBON CHAII\ t ENGTH, Lovg

FIGURil 43.-Minimum Autolgnltion 1 ··rnperature·.~ of Pt ·•.ffin HydrocarL '"~ .11 Air as a Function of Average f:arbon Clll'in .-•nl(th.

In each case, powerful initiators were req11ired to obtain a detonation in relnt, vrly l11rge pip•·-; The energ;y requ!.rem.anis for ignitioll nm reduce•' if oxygen IS used 11.'1 the oxidant in pl!U'I' of air Further, the detonation velocity InCI't\h ''s a.-; the oxygaa conte11t of the atrr~<•sphere , in­cr('<a.~ed. Detonation velocitie.'l uhtuined L Morrison for methane, ethane, prop~t"•'. l··•ta1w, and hexane in oxygen are given in iJ,.,. " 50 (150); similar data obtained by Waymu' r11l Potter are ~ven in figure 51 f·•r n-hepLtuH'­nitrogen-whlte fuming nitric acid , •tpors (f!9). Of Erincipal interest here is the n. gnitude of the detonation velocity; even in air, t1 is velocity

is S• · rre11t I hut pre;, r!l '"ll VflS are net sent OUt aheu of the dct<~nat.on fro•ll Thus, pressure detect '"'' i hat are liSl'f ·I , ., P.\ plosion preven­tion wit• I••Aagratt 'l \\·•v• .•rt• useless with det •na.tio1

With liq I j rueb, I 1 "' htll !I i llg rde depEllldS ;mrt "'' u,, !>liP ol 1 ·~ ·r·z.ulion 11:1d on the

po •. l SJZI' n,,r~~cs· Stlh-i Ill ·l!ld Lrurner (20) , •tl '' show1 that tlw liqu, : ··.;.:rt-;siorl • nte 11 i.~ gl<' . by

(52)

whm'fl , . is the value of v 1:n 11ng•• pooh, f( is n eu: ,ftut, and d is the pool diameter. Tbr~y

FLAMMABILITY CHARACTERISTICS 45

40 , 0 /I Cll

"' / , E ~~ f-(J 30 Methane ~ I

0 I 0 ....J LLJ > (.? 20 -z z 0:: ::::> CD

10

o~-----~·------~------~--------~-------0.6 0.8 1.0 1.2 1.4 1.6

COMBUSTIBLE, fraction of stoichiometric

Fwl!RE 44.--- Burning V£>1ocitil!~ of !\I ethan£>-, EthanP-, PropanP-, and ?l-ll£>ptane Vapor-Air Mixtures at Atmos­pheric PrcBBurc and Room Temperature.

46 l<'LAMMABILITY CHARACTERISTICS OF COMBUSTIBLE OASES AND VAPORS

~ 0 g 300 L&J > <!J z z a:: ::::> Cll

200

150

100L---~----~--~----~--~----~--~--~

0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6

COMBUSTIBLE CONCENTRATION, fraction of stoichiometric

FH;uR•: 45.-Burning Velocitil's of :\[ptharw-, Etharu·-, nnd Proptllli'·Oxyl(<'ll :\fi'ttur<·s nt Atrno,..plH'ric Pr"""un· nud Hoom T<·mpPrnturl'.

FLAMJ«ABILITY CHARACTERISTICS 47

' 40 ', u Q,l

'Z E u

~ 0 0 __, UJ > (.!) 20 z z a:: ::l .:0

10 ' '

0.4 0.6 1 2 4 6 10 20 40 PRESSURE, atmospheres

FroURE 46.- Variation m Burning Velocit.y of Rtoichiometric Methane-Air and Propane-Air Mixtures With Pressure at :.!6° C.

expressed 11"' as:

!'., =0.0076 ( ru•_t heat of ~ombu~tio~l, ill/, ) senstble heat of ,·aportzat!On, tJ./1,

em/min. (5a)

Fi~ure 52 ~in~~ 1\ ~umrnary of the I'" vnlues for tl number of cornbustibl~s, iududing severul puruffin hydrocurbous (21). Of :-;pt•ciul .. ignifi­<'nm•t• here is thllt j.fJ,Ij.// is 1\etlrl'l cur~>•ltlllt (nbout 100) for tlw pt;r,lffin hydrtH:III"hons, so t 11111 t lwir lirwur burning rutt•,-. in I urge Jlool,-. un• ull uhout '. <'Ill pH 111inutt•.

UNSATURATED HYDROCARBONS

Limits in Air Tlw molrculur wt•igbt ... pt•cilil' :,!fll,·ity, und

otlu•r propt•rtit•,.; of the hydrcll'urholl,., l'oll,.;id­Prt•d lwn' 11n' indudt•d in. tuhlt• 7. At room '.ewperat ure and utuwsplwric prcs,-.ure, t lu

lower limits of flammability of the olefius (C.l/2,.) exduding etnylene fall in the range from 4G to 4S mg combustible vapor per liter of air (0.046 to 0.04S oz combustible vapor per cubic foot of air).

The effect of tempt>raturt> on the lower limit uf tlummubility of rthylt>nt> inuir at atmosplwrie prt•ssurt>. ussumin~ 1l t•onst unt limit flume ll'IIIJWrutUrt', j,-. shown hy the <'Urve lnbded "\ "pw11l'tl JH'OJlll~llt ioll of fhllllt'" in fig\11'(' 5a. r-ufort uuutt·ly, ollly dowuwurd llanw propagn­t ion d11 t n urt• 11 n1ilable over 1111 t>xtentlt>d tt•m­pt'rut u:-t• ruuge (2.22): tlwst' tll'l' indudPtl in fi~urt' 5:~. A" iu till' <'ust• of ,-.imilur dntu ob­I uirll'd with lilt' I !111 rH'. t lu'st' t!Pfirw u st ruig-ht lirlt' pundit• I to the "( 'onst ant tinrnr IPlllfH'rH­

tun•," "i. 'pwurd propngution of flanw'' lim·. At:uin, tIll' modifit.•d Burgt'ss- \\'"··t•lt•r· lu w, t'<Jilnt ion (:!:!), gin•,., u vuriutiou in lowPr limit With IPillpt•ruturl' tlwt i..; clo,.;P to tl111t :,!i\'t'll hy tht• "( 'onsttu1t !lamP II'IIIJll'I'IIIUn'" linP, so tlutt Pit l~t•r t'oultl !w ll""'t'd at t t'lll pl'rnlun•,; hdow I hf' .\1'1' of Pthy)t'lll' 1·1!10" ( '). \!,,;·t'o\"t'l', >IS tfll' hmit fill lilt'. lt'llllJt'l'lll tlrt'"' of oll'lin,; llrt' nnt !ott

48

Combustible

FLAMMABILITY CHARACTERISTICS 1 OF COMBUSTIBLE GASES AND VAPORS

TABLE 7.-Propertus of u·nsaturated hydrocarbons

Formula

I Low0r limit In air Sp gr c., Net t;.lf,I---:----;---,---1--...---,----.-

(Air= I) In air ( Kcal) Lu lu L flu L'u U (volpct) inote ~~: --(:-;:- C·'n Rei. ~~! -C-,,- (~) Uel.

Upper limit In air

-------1------------------------ -------·------Etl.ylene ___ ........ - ... -. Coil•---------- 28.0.'i 0.97 6.~ 31A.2 2. 7 0.41 35 (/IS) 36 6.6 700 (!6) Propylene ____ ..... . .. . f'sllt... .... ... .. 4~. 08 l. 45

1

4. 45 ~r.o. 4 2. 4 . 64 46 (/Oil II 2. 6 210 (40) Butene-1. .. _ .. __ ....... ColiJ .... ___ ... 56.1ll 1.94 3.37 t\07.7 1.7 .50 44 (,) 9.7 2.9 270 (t) <11-Butene-2... .. . -~ c,n, __ ...... ___ 56. to I 1.94 3.37 606.0 1.8 .. '13 411 (40) 9.7 2.9 210 tM Isobutylene ............. c,n, ___ -----. 56.10 I 1.94 3.37 fll4.1 1.8 .53 46 (40)1 11.6 2.8 200 (ttl) li-Methyl-butene-1.... .. Csllto _____ ..... 70. 13 2. 42 2. 72 752.3 I. 61 . 5.'\ I 48 (40) 9. I 3. 3 310 (40)

ProKadlene ........... -c,u,_ .. ______ -::-: 40.06~~-4.117---..a.7---;:6- --~~--48-W~~:~~~-~~ ~ 1,3- utadlen~------·-- ..

1 c,u,_....... .. 64.00 1.87 3.67 676.3 :1.0 .64 49 (JOt) 12 3.3 320, (ttiJ

t l"l~esoompiled at Esp1ollive Res. Center, Federal Bureau of Mines. • Calculated value.

u Q)

"' " E u

~-C3 0 ......J I.IJ > (.!) z z 0: ::l ell

500

400

300~----~---._--~----~----~ 0.2 0.4 0.6 1 2

PRESSURE, atmospheres

hm:RE 47.- Variation in Burning V~>locity of f'toi­chiomrotric M1•thanP- and Etltyhme-Oxyg"ll :\fixtures With l'rCSIIure at 26°C.

4

FLAMMABILl'TY CHARACTERISTICS 49 200

~ (..) 100 g UJ > (!1 z z a:: ::::> a:l

50

KEY o Methane • Propane 0 n+teptane Li iso-octane

----r---·

ot::.

Su = 10 + 0.000342 r2

0~----~~----~------~------_. ______ _. ______ ~ 200 300 400 500 600 700 800

TEMPERATURE, o K

FIGURE 48.-Effect of Temperature on Burning Velocities of Four Paraffin Hydrocarbons in Air at Atmospheric Pressure.

0 .__ __ ____, ___ -~----'----.....J 6 8 10 12 14

METHANE, volume·Pt!rCe'lt

Fwt·nt; 4\1 - -lll'tor.ation \"do<'itir-,. of ~h·thane-.\rr .\li~turcs at AtrJHHph<'rie l'n·s~urt•. (Initiator: ,·,o ·;o Jl:r:lflb of amatol C\plo~ive. Pipe dianll't<·r: :ltl.5 lllll.)

diffPrl'rtt fmm t ho,.;l' of pnndlin hydwcurhons, t lit' g'l'llt'rulizt•d gmph for f.,!L 1,.,c' (fig-. :!:l) l'llll bt• :J,;t>J for these un~;tlturu!eJ hydwcurbons.

3.000,

u z E ~ 2,000 u g ..., > z @ 1,500 ..: z. 0 ,_ ..., Cl

1,000

--.--------.-----,

KEY A Hexane

• Butane 0 Propane

• Ethane 0 Methane

500~-----~---~--------------~ 0 10 20 30 40

COMBUSTIBLE. volume percent

Frti!'Rt: ."ofl.-- Dt•tonation \'dori•ic~ of .\IP~hanc-, Eti:ant·-, l'ropanl'-, Butane-, and Hexaue-Ox~~o~:en :\:ixturc.~ ut _\trnosphcrit• l'r=,ure.

50 FLAMMABILITY CHARAC'TEIUS'riCS 01'' COMBUSTIBLE GASES AND VAPORS

J,OOO j" · l

m 01.~00 '"'-E ?"";., -4 f. u 0 -' UJ > X::::., z 0

~

j z: (Mole fraction N2 = 0.5) 0 l:;j 1,500 -0

1,000 0 5 10 15 20

n-HEPTANE, mole-percent

FIGURE 51.-Detonation Velocities of n-Heptane Vapor in WFN A (White Fuming Nitric Acid)-Nitrogen Gas Mixtures at Atmospheric Pressure and 400° K.

FHwa~; 52.--Relation Between Liquid-Burning Hate (Lar!f J-l'nol Diameter) and Ratio of Net lleat of Comb 1 ·lion to SenMiblc Heat of \'nporizatiou.

Limits in Other Atmospheres

Th11 limits of flnmrnu.bility of ethylene, propy­Jen£>, isobutylene, but£>rw-1, :~ methyl l.mtene-1. und hutndiene in vuriow; irH'rt -uir utmosphNeh lll'"e been determined by Jones and coworkers

ModtftCld Burgt•ss·Whf!eler Law

~Upward propagatton Constant flame temperature·· ·~ of flttm~t

0 TEMPERATURE, • C

FwuRE 5:l.-Effect of Tcmpcratore on Lower Limit. of Flammability of Ethylene in Air at Atmospheric Prc~surc.

40

-e ~ 30 a. ci> E :>

~ 20 ... r z w -' >-:I: 10 l:;j

0

Cst

10 20 30 50 ADDED INERT, volume-percent

FIGURE 1>4.-Limits of FlammAbility. c! -l~thylelle­Carbon Dioxide-Air and Ethylmw-N!trogen-Air Mixtures nt Atmospheric Pressure and 26° C.

(100, 101, 10:3), (fif,'s. M-60). The first two figures are modifiCations of the lirnit-of­flttrnmability diagrtuns given in (.~0); the third i>~ essenti,tlly the sunw 11s t.h11t 1•iven in tlw ettrlim· publieution but include~ the experirnentul points. The other· curves were constructed {rom originn.l, unpublished data obtained ut the Explosives Hes. Center, :Federal Bureau of Mines.

Other limit-of-flammability det.enninations huve been rnnde in oxygen nnd nitrous oxide. These du.taure included in table 8 (40, 100, 100).

Autoignition

There have been few determinations of Al'f's of the tmsntumtcd hydroenrbons in uir or ot.her oxidun ts; the u vniluble dultt (il1, 116, l!J 1) arc summarized in table 9.

'FLAMMABILITY CHARACTERISTIC8 51

12~---,.... T %air= 100%-% propylene-% inert

-8 c: Ql ~ Ql Q. cb E

Flammable ::I

~ 6 mixtures a.J N2 z UJ _, ~ 0 a:: 4 0..

0 10 20 30 40 50 ADDED INERT, volume-percent

FIGtrRE 55.-Limits of Flammability of Propyl!'ne-Cnrbon Dioxidl'-Air and PropylC'nc-Nitrogen-'.!r Midutes at Atmospheric Pressure and :.!6° C.

The burning velocity of ethylPne Juts been determined in nir, oKy!!:ell, tmd oxy~en-nitro!!Pil n t mospheres by n umerom; invt~st igntors (3, .'f 7, )ii, (18, 131). In geneml, it is highPr thun tlw huming velocities of the pnraffin hydrocarbons tmdor the same conditions (fig. 47). Sin:ilttr rt-stJit~ IU"e to he expected for other un~ntumtPd hydrtiC'urbons, ulthough the availuble dat1t ure m t.hor menger-.

Stability

:\luny unstlt,umt.l'd hydrocnrbon vapors ean propugate tltUne iu tbe absence of uir at. elevut(•d temperatures and pressures; that is, they have

!J(• ·:'"'·;~~ lirrtit "f 'l.::l:"'l "'"'"~V. Tl-. 0 <0" ('"'"''··

hustibie, lllwe positive heliL~ uf formati1m, t1ll1 (tnble 10) nnd would therefore liberate heat if deeornposmi to the elements carbon un(i hydrog-Pn. EvPn more heat would be lihe.r­nted if gases with a negative heat of for­mation - for exnr>lple, methane-form from the elements. Tn prnctice, tl mixture of products rl'sults upon decomposition of such combusti­bles. For exumple, u propagnting demmpo­~itiou r!'1tdion CUll be iuititLted in pure ethylene Ill tl 2-mch-ID tube at 2:3° ( ~ and pressures aR

low as 750 psig. usin~ 2 grams of guncottou. A reuction Cllll he initlnted at 21" C and prf>~;­sures us low tls 975 psig with 1 gram of guncotton. The demmposition products tl.l'e

52 FI.AMMABn,rry CHARACTERISTICS OF COMBUSTifli.E GASES AND VAPORS

lO ---·----·-r--··-----r----·---·-·--r-·-·----,------····-·--1 %air= 100%-% isobutylene --% inert

8

Flammable mixtures

J

~------~~----~----------'--------~ 0 10 20 zo 40 50 ADDED INERT, volume-percent

FIGURE 56.-Limits of FlammRbility of IRobutylene-CarbC'n Dioxide-Air and Iwbutyle!).~Nitrog.1n-Air Mixturea at A~mosphcrh: Pr831!ure and :i:6° C.

TABLE 8.---Limitq vj fto.mmability of unsaturttted hydrocarbons at atmosphero:,C pre8sur~; ar~d room temperature, in t~Jlume-percent combustible vapor

(L-Iuwer ilmtt; u-nppe·.- !!mil.)

I Jn IIi::-- ---~n oxyg1.•n / In ni_trou: OXlde

Combustible / ·- ____ --~------

-~,~-~~~~~- ~,_:_1--~ Ethylel•A. ______ 2. 7 36 1 2. !l 80 I. 9 40 Propylene._____ 2. 0 11 ,2. 1 .~3 1 l. 4 29 Butene--}-------,1.6 10 I. 7. 1 ~~ ~----- -----But{•ne-2 __ ., ___ 1.7 9.7 t7 I ao ----------

------------~-------- 1 I -

primarily carbon, methane, and hydrogen: approximately 30 Kcal are relc•tsed per wole ot ethylene deeumposed. J>ropylene ytelded simi­laT products following explosive deeomposition durw.g compreesion to 4,860 utmospher~~> (34).

'i'AoL'I!' U.-. .J!finirr,um autoignition temperatures (~{ unsat?J.rr..ted hydroca.rbons a.t a.tmospkcri.c prt..Q.~ure

----·---.,.----Autoignition ten'ptJraturc

-·-------- -·,--------.. -- ---· Combustible In R'r I In o::ygen

T----·--·-r---~ C / ° F · Ref. ° C ° F Uef. ---.--1----,-- ----· ----1-

Ethylenc ......... 490 1 914 (116) 485 go,') 1(116) Propylene .. ___ ..

1

45~ .356 ( 94) 423 1 7931 (1) Butene-! ________ 31!4 723 (1) 310 i 1\90 (I)

Butene-2 .......... ,324 615 (1) ---··j·-----l,:}.Rutadiene ...• '.118 '684 (191) 33.'i 63.'.. 1(191)

---·- I I • l"lgures compiled by E1ploelvM kes. C.Mtor, Fedl!l'al Bur~au o.

M<ne3.

Prope.diene and bn~adiene also decomJJose readily under the a<'tion of powerful iguiLors. Propadiene vapor has ber-n decompo~ed in a

F1 ... AJI1MABlt.lTY CHAHACTE RIB TICS 53

60

" 50

% oxygen~· 100%-% iso\ne-% water va~or

\ \ ..... c: CLl 0

~ 40 IV E ::I

~ rr. 0 30 -a. ~ L&J z: L&J _, j?: ~ a:l 0 en

0

Flammable rnixtur~s

20 40 60 80 100 WATER W~POR, volume-percent

FmuRE 57.-Limits of Flammability of Isobutylcne-Watcr Vapor-O:::ygen Mixturl'@ at 150° C and AtmOI!perio Prossurc .

• ..-.11<'11 ; 1'be at 120° C am' ;;;) psig using a piatinum wire ignitor. Decomposition of buta­diene in an industrial accident resulted in a "popcorn" polymer; the reaet.ion was apparently initiated by an unstable peroxide (4).

TABLE 1 0.--HeatN of formation (Kcal/mole) of un.~aturated hydrocarbons at 25° ('. ·

( 'ombustible: Acet.y 1!-ne ________ .. __________________ .. _ Propndi1•np _. _ _ _ __________________ .. ___ _ MPthyllh1!'ty1Pnl' _______________________ _ 1-3, Butndiorw ________________________ _ Ethy!Pne _______ ~------- _____________ _

i-il~~~~~ ~ -_-~ = = = = = = = = = = = = = = = = = = : = = = = = =: I Rot'a. (/14, Ill$),

illlt'

54. 2 41i. !! 44, 3 26. 8 12. fi 4. 9 .3

ACET' .. '"!..El'.iC h~ DitOCABBONS (CnHzN-2)

Limits in Air

Acetylene forms flammable mixt-ures in air nt atmospheric pressure nnd 25° C, in a range from 2.5 to 100 volume-percent acetylene. Quenched nnd npp~tratus limited upper limits have been obtnined in 1-, nnd 2-, nnd :i-inch­diameter tubes (40), but pure acetylene can propagate flame at atmosphPric pressure in tubes with dinmetcrs of u~ lenst 5 inch(ls. Sar~ent has summarized availu.ble duta on init1al pr~ssure requirements for deflagration and

FLAMMABILITY CHARACI'ERISTICS OF COMBUSTIBLE GASES AND VAPORS

8

0 10 50

detonation through acetylene in horizontal tubes of about .02 to 6 inches ID at 60° F. (89, 185). His curves s.re g:ven in figure 61, which also includes an experimental point from the data of Jones and coworkers obtained in a vertical 2-inch-diameter tube. The existence of this point, at o. pressure below that given by Sargent's curve for a 2-inch tube, indicates that this curve should be used only far horizontsl systems. The point labeled "Industrial explo­siOn" was reported by Miller and Penny (144) o.nd presumably refers to a deflagration. The third experimental point is dis~ussed, along with the detonation curve, in the section on stability.

ADDED INERT, volume-percent

The effect of tempero.ture on the lower limit of flammability was determined by White in a 2.5-cm tube with downward propagation of flame (£22). Although the actual limit values n.re not sa.tisfo.ctory for our purposes, thtlJ' can be used to check the applicability of the L,fL25° ratio data presented in figure 23. The White ro.tio of lower limits nt 300° and 20° C. is 2.19/2.90 =0. 76; the corresponding ro.tio from

FIGURE 58.-Limits of Flammability of Butene-1-Carbon Dioxide-Air and Butene-1-·Nitrogen-Air Mixtures at Atmospheric Pressure and 26° C.

10 .-------.----,-----,----r---l % air = 100%-% 3 methyl butene-1-% inert

FIGURE 59.-Limits of Flamma­bility of 3 Methyl Butenc-1-Carbon Dioxide-Air and 3 Methyl-Butcnc-1-Nitrogcn-Air Mixtures at Atmospheric Pre!!­sure and 26° C.

-c: cu f::! cu Q. cb E ;:,

g ;:;:i-z w ..... ,;:) m ....J ?.: ... l:i:i ::!: ('I')

8

6

•

Flammable mixtures

Cst

ADDED INERT, volume-percent 50

FLAMMABILI'I'l" CHARACTERISTICS 55

% air= 100%-% butadiene-% inert

FIGURE 60.-Limits of Flamma­bility or Butadiene-Carbon Dioxide-Air and Butadiene­Nitrogen-Air Mixtures at At­mospheric Pressure and 26° C.

Flamm~ble mixtures

0

"Constant flame temperature" curve in figure 23 is O.iS. Accordingly, this figure should be sati>'factory for u"e with acetylene. at tempera­tures in the mnge from 20° to 300° C.

The Jm,·er limit of flnmmnbilit~- of methyl­ncetylene (propyne) in air nt ntmospheric pressure is I. i volume-percent, equnl to 0.34 C,, which compnres fnvornbly with the vniue for acetylene (0.:32 C,,). Upper limit im·estign­tions hnve been conducted bv Fitzgernld (liD) in n 2-inch tube nt 20° nnd 120° C' to determine the low-pressurl.l limits or lowest pressures nt which tt tlnrne will propngnte through methyl­ncetylene vapor at these temperatures. He found these to be !iO nnd 30 psig nt 20° nnd 120° C, respectively. In a 4-inch tube, Hnll und Strnker (77) obttlined a !ow-pressure limit of 43 psig nt 20° C. This indicntes thnt the upper limit of flammability of methylacetylene in air is probnb!y less than 100 percent at 20° C and 1 atmosphere.

50 ADDED INERT, volurr;e-percent

The quantities of propylene required to prevent flame propagation through methyl­acetylene-propadiene-propy!ene mixtures at 120° C and 50 and 100 psig have been deter­mined in l-, 2-, 4-, nnd 12-inch tubes (fig. 62), and ut 120° C nnd 100 psig in a 24-inch sphere. As noted, the propylene requirements are strongly affected by tempernture, pressure, and container size. As the tube diameter increases, the quantity of propylene required to prevent flume propng-nt.ion increnses; this efTect is less pronounced in the !urger vessels {dinmetcr grenter than 4 inches) than in the smaller ve>:se!s (diameter less thnn 4 inches). The results obtained in the 24-inch sphere were similar to those in the 12-inch tube.

Limits in Other Atmospheres

G!iwitzky (71), and Jones and CO\\'Orkers determined the efTects of carbon dio;;de and

56 FLAMMABILITY C!HARACTERISTICS OF COMBUS·riBLE GASE!:' AND VAPORS

I I I I I I

KEY Sargent

20 - • 0

Miller anrl Penny (Extrapolated) Industrial explosion

6 Jones and others

10 s~~~~~~~----~--~~~~~~-----L-~--~~~~ 0.02 0.04 0.06 0.1 0.2 0.4 0.6 1 2 4 6 10

DIAMETER, inches

FJGUR'!!i 61.-Effect of Tnbe Diameter on Initial Pressure Requirements for Propagation of Detlagration and Detonation Through Acetyltne Gas.

nitrogen. on the limits of acetylene in air at atmospheric pressure and room temperature. Unfortunately, all measurements were made in tubes that were too narrow to give actual upper limit data. Nevertheless, the resulting quenched-limit data are summarized in figure 63, because they show the relative effects of adding two inert diluents to· acetylene-air mixtures in a 2-incb-ID tube.

Autoignition

A summ'l.l'Y of available a.utoi<>'nition tem­perature data for acetylene, acety1ene-air, and acetylene-oxygen mixtures in clean systems is given in figure 64. They are based on measure­ments by Jones and Miller (110), by Jones and Kennedy in quartz tubes (99), and by Miller and Penny in a 0.5-inch steel pipe, 15 inches long (144). Jones and Miller found minimum autoignition temperatures of 305° and 296" C for a variety of acetylene-air and acetylene­O:\:ygen mixtures, respeetively, nt utmospheric pressure. Miller and Penny report little varin­tion in the nutoigni.tion temperature of acety­lene in a clean pipe at 4 to 26 ntmosphere!' initial pressure. Howe\·er, the presence of 1 gram of powdered rust, scale, kieselguhr, aluminn, silica

gel, or charcoal lowered the pipe temperature required for ignition to a 280° to 300° C range. The pt·esence of 1 gram of potassium hydroxide lowered the pipe temperature still further to 170° C. The impact of a 0.25-inch steel ball fulling ft·om a height of 15 inches against a fragment of copper acetylide produced a bot spot that ignited the surrounding gaseous acety­lene at room temperature and 3 atm11spberes.

Burning Rate

The burning velocity data for acetylenC' in nir obtained by Manton and Milliken at 1 atmosphere and room temperature are given in fi<;urc 65 (188). The burning velocity ranges from n low of a few centimeters per second near the lower limit to a high of about 160 em/sec on the rich side of the stoichiometric composi­tion. Parker and Wolfhard (164-) have found considerable vnriation in the burning velocity of acct,Ylene in various oxidants. The burning velocities in stoichiometric mixtures with oxy­gen, nitrous oxide, nitric oxide, and nitrogen tetroxide were found to be 900, 160, 87, and 135 ern/sec, respectively; for comparison, the burn­ing velocity in a stoichiometric acetylene-air mixture (fig. 65) is 130 em/sec.

FLAM:.'IABlLITY CJ IAHACTEH!STICR 57

12-inch-ID

4- inch-I D

2-inch-1 D bomb,IOOpsig

1-inch-1 D bomb,IOO psig

\

90 80 70 PROPYLENE, volume- percent

FIGURE 62.-Rangc of Flammable Mixtures for MPthylncPt.ylenc-Propudienc-Propylcuc System at 120° C und at 50 and IOU Psig.

The hurnin~ velocities of tu•etylene-nir rnix­tur·es were found to be independent of pressure between 0.1 and 1.0 nt.mospherc (138). Sim­ilt!rly, A~new nnd ,J-raiff (3) nnd Parker and Wnlfhard (164) found th· l1urni:1;., \·eloeities of stoichiometric acetylene-oxygen und a<"ety­lenc-nit.rous oxide mixtures were independent of ;>resstH'e bet ween upproximtttely ()..'j und 2 utrnospiH•res and 0.0:~ und 1 atmosphere, re­sped i \·ely. The huming velo<"itics of st oi<' hio­mct,rie u<"ctylene-nit rir. oxide und al·ct.yl!me­nilro~rn tetroxide ruixturcs inerett:•ed slightly o vrr this pressur·e range O.O:l to 1 a tmosplwr'c (W4).

Stability

A~ :wted, nectyll'ne <'UII propttg-ate llnme in the ubscnee of uir (3/J, 165). The pressures

required for propugntion ut subsonic (detla~ra­tion) and !-lupersonie rutes (detonution) mto the unhum<1d pls ure 1-'.'i,·en for n mnge of pipe f 1: ·"1tlrs i~· 1;crure fil (185). Veflagrution is J:s.:usscd bdefly under Limits of Flnmrnubility; detonation is dis<'ussed in this section.

The eun e lnheled "Dcton11.tion" in figurr n I gi vcs the minim urn pressure required for propngution of n det.orllltion, once imtiut.ed, in tllhes of o.:l to 10 inches diPmeter. In pmc­t il'e, u dt'tonut ion may be initinted directly from n dPflu!!l'ution thut lms proJmgnted through n r!t t ht>r ill-tlt>filll'd disttliH'C, known tlS t lie predctonution or run-up distance. This dis­tunee depends on t.emperttture, pressurP, t uhP dinmeter, condition of t uhe wnlls, nnd on ignition-soureP streng-th. For PXIllllplr, using n fu!'led platinum win• ig"nitor, ~Iiller tllld Penny

58 FLAMMABILITY CHARACTERISTICS OF COMBUSTIBLE GASES AND VAPORS

% air = 100%-% acetylene-% Inert

0 20 40 60 80 ADDED INERT, volurr.e-percent

FIGURl. 63.-Quenchcd Limits or F!nmmnbility or Acetyl'!nc-Cnrbon Dioxide-Air and Acetylene­Nitrogen-Air Mix',;•rcs at Atmospheric Pressure nnd 26° C, O!:>taincd in a 2-lhch Tube.

FIGURE 64-l\.linimum Autoigni­tion Temperatures or Accty­len!'-Air and Acctylcne-oxyKcn mixtures at atmospheric and elevated pressures.

• 0 r:. 0

I

(144) found the predetonatien dist.ance for acetylene in a l-inch tube to b£1 :;a feet at 51.4 psia, 22 feet nt 55.9 psia, 12 r~et llt 73.5 psia, and 2.8 to 3.~ feet nt 294 psia initu.l pressure. Extrnpoh1tion of these dnt11 yields the point in figure 61 for n. very lnrge predetonution distnnce. This point (44 psiJ. nnd l-inch diam­eter) lies fuiriy close to the detonution curve established hy '3nrgcnt (185). The maximum lent.h-to-dinmeter mtios (L/D) ~iven by Snrgent for estnblishing detontttion m ncetylene is plotted arrninst intinl pressure in figure 66. In tubes, hnving 11 diameter great!'r thnn those given nlong the top of the figure nnd hawing powerful ignitors, the LiD mtio will be less than thn.t given by the eurve. Nevertheless, this figure should b!l of usc in giving the outer bound of LfD nnd the npproximntc quenching dittmcter; u better vnluc for the quenching dinmeter cnn be obtnined directly from figure 61.

Although pr!'detonation distunces are diffi­cult to measure nnd cxperimentnl dnta often exhibit much scntter, they nrc of interest in snfety work because they can be used to evalu­n.te the mtlximum pressures likely t.o occur in a aystem due to cascading or pressure piling. -This phenomenon presents a sp··dal problem because the finul pressure achieved in a detonn.-

KEY Oxidant Pressure Tube

Air 1 atm 131 cc quartz Air 1 atm 200 cc quartz Air 2 atm 200 cc quartz Oxygen 1 atm 131 cc quartz

None 4·26 atm ~-inch steel pipe

~egion of autoignition

I

'1 :

20 40 60 80 100 ACETYLENE, volume-percent

FLAMMABILITY CHARACTERIATICS 59

200r-------r-------,------~

?3 u 0 ...J I.IJ > ~ z z c:: ::l CD

0

/\ ; \

I \ I

10 15 ACEn'LE;~E. volume-percent

Fm:::l'.E 65.-Burning V"locity of Acct~lcnC!-Air Mix· tm!'S at Atmospl.cric l'r!'Ssurc and Room Tempera­tUrC'.

tion depends on the initial pressure at the onset of detonation. F..;r example, the maximum pressure to be expP.cted from the deflagration of !l.cetylene at moderate pressures is about 11 times the init,ial pressure (144); the maximum

FIGURE 66.-Maxhnum LID ratio ltC'quirC'd for Transition of a Deflagration to n Detonation in Acctylcn(' Vnror nt ,.,y F and from 10 to 70 Psia. ._,'

to be expected from a dotoDI\tion is about 50 times the initial prese'..lre. As the preRSure eq•Jalizes e.t, ti-e spGed uf sound ill a defl.&.gra­tion, the maximum initit\l pr63Sure to be ex­pected upon tra11si.tic,n from defl.agration to a aetonation is approximately 1 i times the frac­tion of acetylene tha.t bas been burned times the initial precombustion pres;:~ure. Fifty times this pressure is t!lo aJ'proximate maximum pressure that wouM be obtained when a detona­tion occurc;. •;o illustrate thi.8, Sargen" bas plotted the final-~.o-initial pressure ratio (P1/P1) against the predetonat10n distance-to-tube length for acetylene. A similar graph is given in figure 67. 'To use this gr11ph, the maximum predetonation distance to be expe-cted must first be determined f.rom fi~re 66. Th;~ ~:Ez­tance divided by th6 tube length gives the maximum final-to-initial pressure ratio.

AROMATIC HYDROCARBONS (CftHh-e)

Limits in Air

The combustibles considered in this section are listed in tf!-ble 11, with pertinent properties. At atmosphenc pressure and room temperature, the low~r limits of flr..mmability or the aromatic hydrocarbons are approximately 50± 2 mg/1 (0.050± 0.002 oz combustible vapor per cubic foot of nir).

The lower limit of toluene was determined by Zabetakis and coworkers in air o.t 30°,

QUENCHING DIAMETER, inches

2 1

INITIAL PRESSURE, psia

60 FLAMMABILITY CHARACTERISTICS OF COMBUSTIBL•~ GASES AND VAPORS

TAm.E 11.-Properties r~f selected aromatic hydroca.rbons

I I

I -""'"':""-------

Lowpr limit in air I Up(l('r limit in nir I

j C,, in net tlll, I M (Ai~!~) ail~s;ol (£~-~) [,100--,-=--z-~:-;,~---~-;--1<\mnula

---------·---l----1---------------- ----~--~£~~~- _C_n_~-~ _,;~_~_{_ -~~~-- _c_~~-~11:_) lll'tlZI'IH' _ ..

1

Celie I 7S. II :.!. tHl 2. 72 '757. 5,1. :~ 0. 4R 1 47 7. !l 2. fl :wo Toh•,.m·_____ _ C 711, !l2.t:i !i.ISI 2.27 not.5 !.:.! .5:31 50 7.1 :1.1 :110

o-X\·lt•rw.. _ C,ll 10 IOH.Jti ~.1'7 1.\lti !04!i.!l 1.1 .ali 5:1 li.4 :1.:1 :l:.!O EthvllwnzPIH" 1 (',1! 10 lfl(J. lH :l.lj7 I. !Hi 1 10-tS. S ' I. 0 . !it 4S fi. 7 :!. 41 :i40

m-Xvlt·ru· . ____ -I C,H 10 lOti. )(i :~. li7 I. \Hi 110-tll. 5 I. I . !i61 !i:l ti. 1 I :l. :l :320 p-X;·!I'llt•___ C 8H 10 106. lti :l.li7 l. !Hi 1045. 7 I. I !iii !i:l li. li :!. 41 :!40 <'umPnt•____ C.H 11 t:.W.I\1 4.15 1.7'2

1

11\l.j.:.! .S·" .ill 4S fi.!l

1

:l.S :!70 p-C:_vml'nl'. _ ::: _ · ~~ c!OB,. 134. 21 1 4. ti3 1. sa 1341. s . s5 . li6

1 51 u. 5 a. o aso

I Ref. (f47),

-- -r---- ·--- ...... T __ T

FIOt'RE ti7.--Finnl-to-Jnitinl l'rl'f<­I!Urt· Hat ios Vt•\'PiopNI h,v At•l't­vh•m• With ll"lounti:m Inilill­i.ion at \' !lriou~ Points A lung u Tuol'.

300

~ 200 ~

100 -

........_ ___ __._ ____ _,__ ____ ...._ _______ ._L ___ _j

0 0.2 0.4 0.6 08 1 0

100°, and 200° (: (28/i, 247); thr vuri~Ltion in lower limit with tempemture is givrn hy t•quu­tions (:H) and (:~:n deri\·ctl for pnmfJin hydro­carbons, und I he correspondin~ curves of iig11re 2a. For exurnple, 1.-zt~.,. r/ /.J,,. <' wus found to hr 1.07/1.24 or· O.Hii; the mtiu predid1•d by 1 ht• curve in figure 2:~ is O.S7.

The UJIJWI' limits of tht• nro:unti•·s l'onsidPrt>d hert> ut ltl0° (' nrP irwllldt•d in tuhlt• II L.?;/1 Thrsr Wt'ff' obtuiiH•d 1~! tllruosplu•ric prps.;un• in 11. 2-irwh-dianH•IPr tuh!', opt'il nt ont• Pnd. ButlPr urul Wehh ohlttirwd upprr lirrul dutuon n •·uwmPrl'ittl grudt• t'llllll'lll' (!1.1.:~ pl'l t'llllll'r'el

iii llif Ill dP\'Ilted ft'IIIJH'I'IIIllfi'S nlld llllllO!-l(liH•J'JI'

1llld t~lc nt! t~tl prcssurt~s in 11 closed bout h (.1 1).

PREDETONATION DISTANCE/ TUBE LfNGTH

Tht>ir valut•s fllllg'f' r~·om S.S pl'l'l'f'll I C'lillH'Ilf'

(H0° (' und utlll••sphl'ric Jll't•ssurt•) '" IO.S JH'f·· Cf'lll I'Uilll'llt' (J-tti'' {' 1111d ]()f) psig; jli'PASUI'!').

Limits in Other Atmospheres

Tlw !imit~ of tlamlltuhilit,· nl:iaint•d bv Bnr-1-!"·'·n~· (i.'l) nnd h,v .. f,Hif''. (.)0) for J,,;IIZ''IIP­.. Ilrhnu tlioxidf'-nir 1111d hi'IIZP!ll'-llit rogl'll··aiJ· 111ixt lll'f'~ Ill llfiiiiiS(lhPI'II' Jll'f'~SIIl'P lllld :!!"> 0

(' 111'1•

g"i\1'11 i11 fig-urf' tiS; sitnilur dnlt: !11'1' j.!'l\'1'11 for tilt• ln;;t two mixturPs ut nfllll•~phPril' fli'i•s,;urP und ltl0° ( '. Th1• i1u•rtiugo I'PI(IIIl't'IIH'IIIs 111 :,!;," \' ttl'!' appr·nxirnutPiy t liP ,;an11• 11-1 tltn:'l' nf 11-lrt•xtllll' (li~. ;):!). Agulll, it 1-iholllcl rH' llotl'd

FLAM:MABILl'l'Y CHARACTERISTICS 61

lOr-------~------~-------r---

% air= 100%-% benzene-% inert

..... t:: Q) (,J

8. cb

8

E 6 :::1

~ o£ 0 0.. <( > LIJ z LIJ N z UJ Ill

' ' ' ' 0 10 20 30 40 50

ADDED INERT, volume-percent

1-'IOt'l\t: 611.-·-Limit~ of Flnrnmnbilitv of Benzene-Methyl Bromide-Air Mixtnrea at 25° C and Benzene-Carbon Dioxid<•-Air and Benzt•ne-Nitrogen .. Air Mixtures at 25° and 150° C and Atmospheric PreaeurP.

tb!lt the methyl bromide dnta Kre unt CDnsistent with thos(;, obtnirwd by Hili {C'ornptlre figt-J. 28 and :1:l). Thest• l11.tter dntu (84) wer·e used to eonstru<'l the nppmxirnnte (broken) tlllntll11l­bility c·un·es for tht' hl'llZI.'ne-mt'thyl bromide­uir !'1\'st.em.

Tfw de<·reasf.' in the minimum oxy~en require­rn£>nts fnr fllllllt' propuglltion (from 14.2±0.:~ voiUIIH'-pPrC'ent ut 25° ('to};{ l±O:J ''olumt'­IH'I'l'Nlt ut 150') iu 11 c11rhon dio.xide-nir ntrnos­phere; from ! 1.4 :tO.:i ,·olume-1Jei"<'<'nt ut 25° (' to J(J.l :± 0 :) volumP-Jli'J'<'<•nt 11t 150° in u nit.rog,~n-uir ttt.moHphNt') ill witltin t ht• l'llllfrt>

f>rt><lil' I~·~~ hy t h <' mml ifif•tl Bur~t'S!I· W ht>t•lt>r uw (equn1ion (:lr>), fiJ!. :,?;{).

Tht• linutR of flumlllllhilit \' of urt hoxvJ(,Ilt' (( ·~H 1 • (< 'Hlill-wn~rr"lt~·drogt>il pt•roxide · Joix­turl'!:l wt•rt• cktHIIIIBNI 111 l.'i4" (' und 1 tilllln!l­

ph••rt> prt'~"~~''llll't' hv :\fIll' I illdill, L11.11~, und Z~tlwtllkiN U-V>). 'thf• dtilll nrr pre~ntf.'d in n triungulur plot in figure 119; <·om positions are

expressed in mole-percent as in the original prt~sentation. Thif· system has no low.er limit, mixtures, as a fhune can he initiated in hydrogen peroxide vapors (186). As a 90-weight-percent hydrogen peroxide was actually used to obtain theRe flammability d11ta, all eompos1tions were rtlleulated to yield ,·ulues ba~d on a 100-percent hydro~en pen•xide content. This could be done ht~re bocauf!e only three cemponents are consid­(lred. Wht're four c·ornponents are r.onsidered, the flummnhility t.iatn cnn be presented in a thr('le-dimen!lionul plot; if two of the eompo­flt•niR nppt't~r in fixed proportions, t\ triungular plot <'ltn be URtld with the two components (for t'.XIIIl.lple, 90-wt•iKht·perc·ent hydrogen peroxide) eonRuiered as a Rm~l~· ('.omponent. ~ueh " plot is pr('IKt>J\ted in figurt• iO lor 90-weigbt­flPI'C'l'lll hvdrogt111 peroxide-ort.hoxylene-formie ndd (H('(){H{} 1\t 1.'14° (' 111Hl I "atmosphert>. This was l'onsidered to he " plane in a regular tetrahedron in the originlil art.icle and is there-

62 FLAMI.\fABILlTY CHARACTERISTICS U!• CvMDUSTIBLE GASES AND V .u'OnS

Composition line formed with 82.6 mole % (90 wt %) H2 0~

FrouRm 69.--Limita of Flammability of H 10rC,H,. (CH3),-H 10 at 154° C and 1 Atmosphere Pr61111ure.

fore not 11. regular triangle. As before, onl,r an upper limit curve is given because 90-welght­percent hydrogen peroxide is flammable. In addition, a calculated curve based on Le Chate­lier's rule is given, as is the upper limit curve obtained wit.h decomposed hydrogt~n peroxide. Decomposition of the peroxide lowers the up~er limit appreciably and yields a system winch has a lower limit of flammability (not deter­mined in this study).

Autoiqnition

The minimum autoignition temperatures of a series of aromatic hydrocarbons in air at atmosplJeric yressure are given in figure 71 as a function o the correlation parameter L.,. This parameter was determined by use of equation (49), treating the benzene ring as a

-CHa group ($,41). When the benzene ring contains two side groups, L.,. is determined first for the side group that yie!ds the largest average value and to this is added ~. ~. or Y. of the average chain length of the second side group; (~, ~. and X correspond to the ortho-, meta-, and para-positions, respectively). Th,. data again fait into high- and low-temperature regions (fig. 43).

Burning Rate

Burning rates and detonation velocities of benzem1 in air and oxygen appear to be ap­proximately the same as those of the higher paraffin hydrocarbons. For example, the re­sults of Golovina and ~~yodorov ($11) show that the maximum burning velocities of benzene in nitrogen-oxygen mixtures range from about

FLAMMABILITY CHARACTERISTICS

... 6

I I

0~~==~====~~~==:;~~;;~~==~~~~~~~ .. ~~~~~--~~--~~100 100 80 60 40 20 0

90 wel1ht-percent H 20 2 , mole-percent

F1o uu 70.-Limits of Flammability of 90-Weight-Percent H 10rC1Ht . ( CH 1) rH COOH at 154,° C and 1 A tmoephere Pr8118ure.

295 em/sec in oxygen to 45 em/sec in air; the maximum burning velocities of hexane in v&rious nitrogen-oxygen mixtures range from about 260 em/sec in oxygen to 40 em/sec in air. Similarly, Fraser (6l) found the maximum detonation velocities of benzene and n··octane i11 oxygen to be 2,510 and 2,540 m/see, respectively.

ALICYCUC HYDROCARBONS (C"Hh)

Limits in Air

A tmmmary of the pertinent properties of :some of the membel'H of the serieti is given in

table 12. The lower limits of flammability in air at atmospheric pressure and room tempera­ture fall in the range from 48±3mg/l (.048 ± .003 oz combustible per cubic foot of air). By volume, this is equivalent to u.pproximately 0.55 C,., which is the same as for paraffin hydrocarbons. The ratio of the upper limit t.o G,, appears to increase with molecular weight.

According to Jones (40), the lower limit of cyclohexane in air at atmospheric pressure and 26° C determined in a 2.0-inch tube is 1.26 volume-percent. Under the same conditions, Bu~oyne and Neale (SB) found the lower limit to be 1.34 volume-percent, using a 2.5-inch tube. Matson and Dufour (141) found the

64 FLA.M:M..Um .. tTY CHARACTZR.l8TIC8 OF COidBUBTlBL& GAt:iES AND VAP(Il'S

(.)

• L£I a: ::;)

~ 0:: L&J r.L. 2: UJ ~

z 0 E z ~

~ ::;) < ~ ::;)

:E z :i

575

525

475

425

375 0 1

-- .. --~----r--------1 I

-l

FroUBII 71.-Minimum Autolgnitlon Tsmperaturee of Aromatic Hydrocarbol1.8 in Air 8ll a Function of Correhlt.lon Parameter L. ••·

TABLE J.2.-Properlus of selected alicyclic hydrocarbons

Combllltlble Formula

CyelogropanP .• ___ .... ___ CaH•--Cydo VIIID<' •.•..... --- c,u,_.: ::. ::: Cyelo~ntane ........... CoH 1, ••••...• Cyclo •anc ... _ . . . . . Coli 11- ••........

t/.•thylc~cylht><l\ne..... c,u,. ....... ~·:~~·\::·- ... I ~·::1::··· • E!hylcyclo ntanP. . Crlllf ....... rr.tby!~yloot=:xane--..... Cal! II--- .....

• Calculated value. s P•0.6 atm. •1-130" c.

I M

42. 0!1 ' 116.10 70.13 114.16 114.10 98.18 1111.11! g(j,IM

112 21

<~C!'1l c •. In air

(vol pet)

------1.4& 4. 45 1. U4 3. 37 2. 42 2. 72 2. 91 2. 27 2. 91 2. 27 3. 39 1.116 3. 39 1.116 3.39 1.116 I. 71 I. 71

lower limit to be 1.12 volume-percent ut 21° C in a 12-inch diameter chamber about 15 inches long: however, there iH evidence that they did not use the BIUne criteria of flammability as did the other authon~; only one ob:lervu.tion window was provided at the top of a rather squatty chamber, whereas with the glas:~ tubes used by Jones and by Burgoyne and Neale the flame could bP observed along the entire tube. Ac-

l.ower limit In air Upper Umlt In air Nett.H,

(!:!) Lu Lu L u .. u (vol c •• (~) Ref. (vol Uu (~) Ref. pet) pet) c ••

-----------------4M 2. 4 I O.M 46 (107) 10.4 2.3 220 (107)

1600 1.1! .&6 46 (I) -------· -------- -------- ------740.1! 1.~ .M 48 (I) --- ... "3."4 --- ----

(~iJ I!KI. 7 1.~ . 67 49 (40) 7. s 320 I KilO 1.2 .63 46 I (,0) 7. 7 3.4 310 (,0

I Hrl4 1.1 .&6 491

(I) 6. 7 3.t 310 (I) 1026.0 1.1 . &61 49 (40) 6. 7 3.4 3111 (I) 1032.6 1.1 .116 49 {40) 16.7 3. f 310 (40) 1173. 7 '·us .611 tll UO) •e.e 3.9 360 (40)

cordingly, the data of Jones and of Burgoyne and ~ eale are used here.

Limits in Other Atmospheres

The limits of flammability of cyclopropane­carbon dioxide-air, cyclopropane-nitrogen-air, and cyclopropa.nc-helium-a.ir mixtures at 25° C and atmospheric pressure are given in figure

FLAMl!4ABILl'I'Y CHARACTERIBTIOS

12r-------~------:r-------T------~------~

%air= 100%-% cyclopropane-% inert

FIGURE 72.--Limits or Flammr.­bility of Cyclopropane-Carbon Dioxide-Air, Cyclopropar.r.-Ni­troi('n-Air, and Cyclopropli\ne­Hdimn-Air Mi::<turcs at. 25° C and Atmospheric Pressure.

flammable mixtures

0

72 U06). 'rhe first two curves are similar to th(lse obtained with !lRraffin hydrocaroons (fig. 35).

Thfl limits of flammability of cyclopropane­helium-oxygen and cyclopropane-nitrous oxide­oxygen mixtures at 25° C and atmospheric proo­s.tre are given in fi~ure n (106). The latter curv11 tiiffcrs from the former, as b11!h Rdditivoo are oxidants (Qxygen and nitrous oxide).

The limits of flaroma'bility of cydopropane­heliunH;itrous oxide mixt.ures o.t 25° ( ~ ttnd atmospheric pressure are gh·en in figure 74 (JOfJ). Here the minimum oxidant. concentration (nitrous oxide) required for flame propagation is approximately twice the corresponding con­centration o£ oxygen in the system!! cyclo­propane--helium-air (fig. 7Q) and cyclopropane­holium-oxygtm (fig. 73).

ADDED INERT, volume-percent

ALCOHOLS {C .. H:. .. +tOH)

Limits in Air

50

The alcohols considered here are listed in table 13 together with L~o and Uno. The ratios L31o/C,, are approximately 0.5. How­ever, the L (mgfl) values decrease with increase in molecular weight. If L* is taken to be the weight of combustible material (exclusive of the oxygen in the moleculfl) per liter of air, then for the simple alcohols:

M-16 L*=L-M-· <54>

This eq_uation gives the valueR listed in pare~­theses 1n the mgfl column; these are m fall' agreement with the values obtained for the

66 FLAMMABILITY CHARACTERISTICS OF COMBUSTiBLE OASES AND VAPORS

50

--,--·-~

% oKygen • 100%-% cyclopropane-(% He, or N20l

Flammable miKtur~s

NITROGEN OR NITROUS OXIDE, volume-percent

FIOURII 73.-Limits of Flammability of Cyclopropane­Bellum-Oxygen and Cyclopropane-Nitrous Oxide­Oxygen Mixtures at 26° C and Atmoepheric Pressure.

40r------.------,-----~

HELIUM. volume-percent

FIOURII 74.-Llmite of Flammability of Qyclopropane­llellum-Nitroue Oxide Mixtures at 26° C Rnd Atmos­pheric PreBBure.

saturated hydroc&.rbons. Approximate L (mg/ I) values can be obtained from the higher hydrocarbon values given in figure 22 by multiplying these by the ratio M/(M-16). Further, figure 19 can be used to obtain L• and L values in volume-percent. For example, at 26° C, L• is about 47 mg/1 from figure 22; the

corresponding La~· from figure 19 for ethyl alcohol (M=46) is 2.2 volume-percent. Then, from equation (54), Lis 3.4 volume-percent; the measured value is 3.3 volume-porcent.

The lower limits of methylakohol have been determined by Scott and cowork~rs at 25 °, 100°, and 200° 0 (192;. The values at these three temperatures are 6.7 6.5, a.nd 5.9 volume-per­cent, re.<~pectively. The calculated values ob­tained from the modified Burgess-Wheeler law (fig. 23) at 100° and 200° 0 are 6.4 and 5.8 volume-percent, respectively.

Limits in Other Atmospheres

The limit-s of flammability of methyl alcohol­carbon dioxide-air and metnyl alcohol-nitrogen­air mixtures at atmospheric pressure and 25° and 50° C are given in figure 75; flammability determinations on mixtures containing more than 15 /crc6nt methyl alcohol vapor were conducte at r,oo C. The maximum amounts of carbon dioxide and nitrogen required to prevent flame propagation in these mixtures

l

---,--- -r---

~

" % air:: 100%-% methyl alcohol-% inert

,, ,, ,',

\ \

~ 25 \ ' \ \ ~

-~ \ ',

\ \

\ ' \ ',

Flammable \ ' Saturated at mixtures ~ 25" C and 1 atm _

10

l 0 ----~10~----2~0----~3~0----~40~--~50

ADDED INERT, volume-percent

FIGURE 75.-Limits or Flammability of Methyl Alcohol­Carbon Dioxide-Air and Methyl Alcohol-Nitrogl'n­Air Mixtures at 25° C and Atmospheric Pressure. (Broken curve at 50° C and atmospheric pretl8ur('.)

FLAMMABIJ,ITY CHARACTERISTIC8 67

TABLE 13.-Properties of selected 8imple alcohold

Combustible

Methyl alcohol.. .........

Ethyl alcohoL ...........

n·Propyl alcohol.. .......

n·Buty: alcohol ..........

prl·n·Amyl alcohol.. .....

n·Hezyl alcohol.. ..... _. _

•L••LM-16, M

•t-60°,

Formula

CH10H .........

Col110H ........

CIH!OH ........

CoHtOH .........

C1HuOH .......

ColluOH .......

'At saturation teruparature.

M

82.04

48.07

60.09

74.12

88.16

102.17

,:~!1) c,, In air

(VOl pet)

------1.11 12. :m I. 69 6.68

2.07 4. 46

2. 66 3.87

3.04 2.72

3. 68 2.21

were compared with the corresponding maxima for paraffin hydrocarbons (figs. 28-35); it was found that appreciably more inert is required to make mixtures contaming methyl alcohol non­flammable. Conversely, methyl alcohol re­quires less oxygen to form flammable mi"tures, at a given temperature and pressure, than paraf­fin hydrocarbom do. This may be due in part to the oxygen of the alcoho.l molecule. For the simple alcohols, we have:

C,.H2n·r~OH+I.5n02-+nC02+ (n+ J)H20. (55)

Thus, the ratio of oxygen required for complete combustion of an alcohol to that for complete combustion of the corresponding paraffin, equation (22), 1s:

R=~· a, 3n+I (56)

When n=l, this ratio is 0.75. The correspond­ing ratios of the experimental minimum oxygen values from figures 75 and 28 are 0.82 with carbon dioxide and 0.85 with nitrogen as inert.

The limits of flammability of methyl alcohol­water vapor-air were obtained by Scott (191!) in a 2-inch-ID cylindrical tube at 100° and 200" C and in a '4.9-liter cylindrical bomb at 400° C and 1 a.tmosphere (fig. 76). Similar data were obtained by Dvorak and Reiser in a 2.2-liter apparatus at 100° C (53).

The limits of flammability of ethyi alcohol­carbon dioxide-air and ethyl alcohol-nitrogen­air mixtures were obtained at 25° C and atmospheric, or one-half atmosphere, pressure as noted (fig. 77), Additional flammabilitv data, obtained for ethyl alcohol at 100u C ·and I atmosphere are given in figure 78. Flammabil-

Lower limit In lllr Upper llmltln air Net.).TI, --· (!:;) Lu Lso

L u .. u. u (VOl (y) Ref. (Vol '!!!!) Ref. pet) ~ pet) c., (I.

-------------·----IIIII 6. 7 o. &6 i 108 } (40) 13tJ

"! }(116 I 62 14()6

306 3.3 .1!0 70 } (40) ··~

2.9 480 ~(118 '46 1310

~ 12.2 .4V i 60 } (40) 114 8. 2 400 (4/}

'" 1310

696 11.7 .110 67 } (') •12 .. -- ~--- . (I) '46 ------·-742 11.4 .61 { 116 } (I)

...... :~_,:::::::: '46 ........ 1 .... •888 1.2 .63 { 66 } (1)

'48 •U•••••• •••••

•t-too• c. • Figures compUed by E.QJioelvee RA. Center, Federal Bureau ot

Mines. • Calculated value.

0 20 50 WATER VAPOR, volume.,.rcent

FIGURE 76.-Limits of Flammability of Methyl Alcohol­Water Vapor-Air Mixtures at 100°, 200°, and 400° C and Atmospheric Pressure.

ity data for the syst,ems tert-butyl alcohol­carbon dioxide-(lxygen and 2-ethylbutanol­nitrogen-oxygen are given in figures 79-81.

Autoiqnition

The minimum autoignition temperatures in air and oxygen of a number of alcohols at atmospheric pressure are given in appendix A. Comparison of these values with those of the corresponding paraffins (methyl alcohol and methane; ethyl alcohol 11.nd ethane, ate.), shows that the AIT values of the alcohols are ger.erally lower.

68 FLAMMABILITY CH.ARAC'rERISTICS OF COMBUSTIBLE OASES AND VAPORS

20

~ %air • 100911-% ethyl alcohol-% Inert

"' ,, ,,0 '" b. "'., 0

lt...q_ ........ Flommable ....,_ ' mh<lures .._ ......_ , No

C$1 COz / "'< ....._

o~----~1~0----~2~0~--~3~0------~~----~so ADDED INERT, volume-percent

F10un 77.-Limite of Flamrnabllltv of Ethyl Alcohol­Carbon Dioxide-Air and Ethyl Alcohol-Nitrogen-Air Mixturee at 25° C and Atmospheric Pressure. (Broken curves at one-half atmosphere.)

25r------,-------T-------r----~

$fi air= 1009£-9£ ethyl alcohol-% water

0 10 20 40 WATER VAPOR, volume percent

Fiouu 78.-Limitll of Flammability of Ethyl Alcohol­Water Vapor-Air Mixtures at 100° C and Atmospheric PreG~ure.

Burning Rate

The burning velocities of methyl and iso­propyl alcohol in air were determined by Gibbs and Calcote for u. range of mixture compositions at 25° C; the maximum burning velocities were found to be 50.4 and 41.4 em/sec, respectively (68). These investigators also obtamed the burning velocities of methyl and n-propyl alco-

%air • 100%-% alcohol-% water vapor

0 10 20 30 40 WATER VAPOR, volume-percent

FJGURII 79.-Limite of Flammability of tert-Butyl Alcohol-Water Vapor-Air Mixtures at 150° C and Atmoepheric Preseure.

60.-----,------. %oxygen= 100% -% alcohol-% C02

0 20 40 60 CARBON DIOXIDE, 110tume-percent

FloURIII 80.-Limite of Flammability of lert-Butyl Alcohol-Carbon Dioxide-Oxygen Mixtur!'l! at lli0° C and Atmospheric Pressure.

hoi at 100° C; the maximum values were 72.2 and 64.8 em/sec., respectively. These values

FLA.MMABl'Lri'Y CHAR/ r.TESIS'l'ICB 69

60 -·-;·~:-;:~~~)-eltlyibut•noH~ nltroll'n

Fl•mm"ble MIC'l ~~ mllrt\<rtl 9.3"' \

\ \

0 20 40 60 NITROC.EN, 110lume-percent

\

FlGURil 81.-Limits of Flammabnlty of 2-Ethyl­butanol-Nitrogen-Oxygen Mixtilree at 150° C· and Atmospheric Pressure.

are in fair agreement with the corresponding values uf the paraffin hydrocarbons.

The methyl alcohol hquid-burning rate ob­tained from equation (53) is in fair agreement with the.t obtained experiment.alll (fig. 52). The relatively low tJI,jAH. ratios .or the alco­hols indica.tes that they should be characterized by low-burning rates in largo pools.

ETHERS (C,H21&+10C,.H2wo+l)

Limits in Air The properties of a few common ethers s.re

listed in table 14. Unfortunately, the limits data show appreciable scatter, so it i3 difficult to establish any general rules with the given data. However, as a first approximat.ion, the Ltft/G., is about 0.5 for the simple ethers.

Limits in Other Atmosphereo

Becaus~ of the importance of ethers as anes­thetics, lunits of flammability were determined in several atmospheres. The limits of the sys­tems dimethyl ethil!lr-Freon-12 (CCI2F2)-air dimethyl ether-carbon dioxide-air, and dimethyl ether-rutrogen-air obtained by Jones and co­workers are given in figure 82 (114); the limits of the syst~ms diethyl ~ther-carbon di­oxide-air and diethyl ether-nitrogen-air are given in figure 83 (£6, 1W, 108), Cool flames exist above the upper limit as noted; the upper

40 ·---r----T--....----..-!C air"' 100%-% ether-% Inert

0 50 ADDED INERT, volurn•percent

Frouu 82.-I.Imits of Flammability of Dimethyl Ether­Cart>on Dioxide-Air and Dimethyl Ether-Nitrogen­Air Mixtures at 25° C and Atmoapht.'ric PreBBure.

40

0

% air= 100%-% ether-% in--t

Flammable mixtllres

Cool flames

10 20 30 40 ADDED INERT, volume·perce~•t

FIOURE 83.--Limits Qf Flammability of Dfethyl Ether­Carbon Dioxide-Air and Diethyl Et.her-Nitrogen-Air Mixtures at 25° C and Atmospheric PreBBure.

!imit of the cool flame region in air is 48.4 vol­ume-percent, according to Burgoyne and Neale (£6). 'rhe limits of the systems diethyl ether­helium-oxygen and diethyl ether-nitrous oxide­oxygen are given in fi~ure 84 and the limits of diethyl ether-heliv.m-mtrous oxide are given in figure 85 (106). Again, as with the alcohols more inert is needed to assure the formation ol nonflammable mixtures than is needed Cor the corresponding paraffin hydror.nrbons. Also, cool flames are encountered at lower tempera­tures and pressures.

Comparison of curves in figures 84 and 85 shows that the minimum oxidant requirement for tlw formation of flammable diethyl ether­helium-oxidtlllt mixtures is approximately twice

70 FLAMMABILITY CHARACTERISTICS OF' COMBUSTIBLE GASES AND VAPORS

TABLE 14.-.Properties of selected ethers

CombusUblft

lmethyl ether .•.••..••.

letllyl ether •• __ ... __ ...

D

D

E

D

D

thy! propyl ether .......

l-1-propyt ether .........

I vinyl ether .............

M-16 'L"•L -xr- ·

Formula

CH10CH1 ......

c1H1oc,H1-----

C1H10CaHr •....

c1n,oc1Hr .....

c1H1oc1R1.-- ..

• Cool ftamea: Ua••63 vol pot.

100

M (lf.!t)

---46.07 1.60

74. 12 2. 66

88.16 3. 28

102.17 3. 15.1

70.00 ~.42

%02 = 100%-% diethyl ether-(% He or N20l

'E II ~ !. .. E

~ a:' .... :c t;; ..J >-:c t;; i5

0 20 HELIUM OR NITROUS OXIDE, volume-percent

I c ..

In air (val pet)

---· 6.83

3.37

2. 72

2. 71

4. 02

100

FIGURE 84.-I.imits of Flammal•iiity of Diethyl Ether­Helium-Oxygen and Diethyl Ether-Nitrous Oxide­Oxygen Mixtures at 25° C and Atmospheric Pressure.

as great with nitrous oxide as with oxygen. However, if 1 mole of nitrouR oxide furnishes one-half mole of oxygen during combustion, then the minimum oxygen contents in the two cases are nearly equal. Unfortunately, the available data are too meager to permit a more detailed comparison.

Autoignition

In generv 1, ethers are readily ignited by hot surfaces. These combustibles usuall;Y have a lower ignition temperature in air and m oxygen than do the correspondin~ paraffin~ und alcohols. The available al'tmgmtion tempt'ra­ture data are included in ap!J"·ndix A.

Lower limit In IUr Net t;.ll, ------(Kcal)

mole Ln Lu L (vol c •. (o/) Ref. pet)

-------- -------lil6 3.4 0. 62 { 72

} IU I 47

1m 1.9 '66 { 64 } (~()) II\()

1760 1.7 liS } (18) 136

•ooo 1.4 '67 60 } (40) I 61 M l

I I, 770 1.7 '42 I~} (117) I

1 Calculated value. • Cool names: U11>l6 vol pet. I Ref. (/66),

Uppt~r limit In air ----

r!u u .. u (val c .• (~) pet)

--------71 4. I 760

'36 II 1,880 . ~ 3. 3 800

7 .. Q 3. 6 290

71 6. 7 I, \60

------,----------r--· -----,-----c % NzO = 100%-% diethy! ether-% He ... l:'! <1> 0. <i> E :::> 0 >

o::' w J: 1-w ...J > J: 1-w c

0 20 40 HELIUM, volume-percent

Ref.

(1/4)

(40)

(IB)

(40)

(91)

80

FIGURE 85.-I.imits of Flammahility of Diethyl Ether­Nitrous Oxide-Helium Mixtures at 25° C and At­mospheric Pressure.

Since the ethers tend to form peroxides under 11 variety of conditions, they ma~ appear to be unstable at room temperature (233).

The properties of several esters are listed in table 15. The ratio of the lower limit at 25° C to the stoichiometric concentration is about 0.55 for many of these compounds. This is the same ratio as in equatiOn (21) for paraffin hvdrocarbons. The lower limit values ex­pressed in terms of the weight of combustible per liter ef a.ir (see section about alcohols) are li!'tt'd in parer theseG under L(mg/1). These are larger than the corresponding values for the hydrocnrbons and alcohols. The inert require­rnt'nts and minimum (,xygen requirements for the fir:.;t memht'r of the series, methyl formate, nrP rwt>.rly t lw snme as for methyl alcohol and dinl('thyl ether (figs. 76, H2, 86). This is not

FLAMMABILITY CHAHACTElUSTICS 71

TABU 15.-Propertie.~ of selected esters

Comhusllblo Formula

-------·--- -------Methyl lornmtt• .. ___ .. IICOOCII, .••..

Ethyl lormutt• ... .,l!COO<'all! .... ---

n-llutyl lormuto ... .. II C'OOC,IIo ..... ---· Mcthylllct•tn,e ..... ___ .

Ethyl Be<> tate_ .• _ .

n-l'ropyl acetnt~ ........

n-llutyl acetate ...... _ ...

II·Amyl acetate .... _ ... _ ..

Methyl propionate. -----Ethyl propionate .. ____ . __

I L·-L·~-32 . M

• Calculated value. I 1=00° C.

C'lhC'OOC'Ih ...

CJ!,COOC'al" ..

C'lhCOOCall? •.

C'lhf'OOC',IIt ..

Ci!,CQOC,llu.

CelloCOOC'Ih ..

c,u,cooc,n,.

Ap. gr. c .. M (Air-1) In ulr

(vol pet)

--- ·---- -----60.06 2. 07 u. 48

74.08 2. btl 6. u~

102.1~ a. !13 3.12

7oi.OK 2.110 ~- 66

88.10 3. 04 4. 02

102.13 3. !13 3.12

116.1tl 4.01 2.M

130.18 4. btl 2.16

88.10 3.04 4. 02

102.13 3!13 3.12

true of the othe;.· ml'rnbers for which data comr,il~d at the Explosives Rese1\rch Center are available--isobutyl forrnat.e und methvl ncetate (figs. 87, 88). Accordingly, it is rather difficult to make additional generalizations for this series.

Low~r limit In air Upper limit In air

Net AU, --------~------- ----.-------

<~~rD J.,.

~~ L Uu u .. [! (vol <"'n Rei. (vol (l~lR) Hel. pet) c,, pet) r.,,

-------·---- ------ ------219 6.0 0.!13 I 142 }<til) :13.0 2. 4 HOO (1// \ 100

367 2. M .110

~ U6 l (40) 16.0 2.8 630 (40 1M

'660 1.7 .64 7U l (40) H. 2 2.6 410 qo 1110

31>!! 3. 2 . ~7 { 106 ~ (40) 16.0 2. H 630 <40 160

2 71 1104 2. 2 . 6~

~ 88 <m 11.0 610 (176 1110

1611(1 l.h .I>!! M3 } qo> • 8.0 2.6 400 qo I 67 • s.o I '1.4 .M {

73 l (I) 3.1 4110 (') ---------- 163

'1.0

:]1 66 } (I) 17.1 3.3 440 (I) ---------- I 49

2 .• 97 ) 13.0 '3. 21 1180 (40 ···-······ 162 (40)

'6110 1. 8 ~~~I} (40)1 11.0 '3. 6 ~10 (4n

• t-100° c. • FlgurescompU~d by Explosives Hes. Center, Federal Bureau of Mines. •P•0.6atm.

The auto ignition temperatures of many esters in air nnd oxygen at atmospheric pressure are givPn in appendix A. In general, the AIT valuE's of the esters are lower than are those of the corresponding paraffins.

% air= 100%-% methyl formate-% inert

FIGURE 86.-Limits of Flamma­bility of !\I ethyl Format-e--Carbon Dioxirle-Air and Methyl Formate­Nitrogen-Air Mixtures.

Flammable mixtures

5

0 50 ADDED INERT, volume·percent

/2 JI'L.\MMAB!l.lTY Cl!JiRAM'E!U8TICf\ OF' COMBUS'l'IBLE OA8tt'l ANI> Vllf'ORI!I

Frou .. 87.--Limtt.e of Jt1.u:cmab!l­lty of llobutvl Jt'orma~Carbon Dlo'ldde-Alr and Ieabut.yl For­ma~Nft.ropn-.Air Millturee.

Frouu 88.-Llmlt" o! Flammabll· lty of Methyl Aoetate-Carbon Dloldd&-Air and Mllthyl Aoeta~ Nlt.ropn-Air Mlnuree.

10

8

l 0

Flammabll! mixtures

10 20 30 ADDED INERT, volume-percent

L _I 40 50

--r-----,------.

% air= 100%-% methyl acetate-% inert

~----~--.~-----~~----~~------~J 0 10 20 30 40 50

ADDED .INERT, volume-percent

FLAMMABILITY CHAitACTERISTICB 73 <' 0 · ·-r· ·- ·· 1 ·- - r·- - · 1 ···---,--- · -.-·· ·· --,---,-- --.-- --·- ·r··--·--r-·--·r---r-···- T ------,------T---,--

flammable m1dures

E 1.8

<1>

~ ~ E " ·c;

70.5 mole % MEK + 29.5 mole % toluene ,. ci 0 ~ < > .....

14 .... ---Ill ~

35.6 mole % MEK + 64.4 mole % toluene (/) :::1 al ~ 0

~- :::-Expenmental

u 12

--- Calculated

Toluene

--1.0

20 40 60 80 100 120 140 160 180 200 TEMPERATURE. "C

Fmuu 89.-Effect of Temperature on Lowar Limits of Flammebility of MEK-Toluene Mixturee ln Alr at Atmospheric Preesure.

Pro\)E>rties of some aldehydes and ketones are given m table 16. The ntio of the lower limit at 25° C hair to the stoichiometric composition if, 11pproximately 0.5.

Zabt>takis, Cooper, and Furno found that the lower limits of met byl ethyl ketone (MEK) and ~U;K-toluene mixtures vary linearly with temperature between room temperature lind 2tl0 C (£15;. A summary of these data is given in figure 89; broken curves in this figure were obtamed from the modified Burgess­Wheeler la~·, r'luation (33), taking the lower

limit at 100° C a.s the reference value. Similar <.lata were obtained for tetrahydrofura.n (THF) aud THF'-toluene mixtures (fig. 90). In addi­tion, it W~s.t~ shown that the systems MEK­toluene a.nd TH_."'.toluene obey Le Chatelier's law, equation (46). Calculated and experi­mental values for the preceding systems in air a.re given i11 figures 91 and 92.

The limits of the systems acetone-carbon dioxide-air, aelltone-nitro~n-air, MEK-chlorc­bromomethane (CBM)-a.1r, MEK-ca.rbon di­oxide-air, and MEK-nitrogen-air are given in figures 93 and 94. The datu. in these fi~cs were obt&ined by Jones and coworkers (198).

TABLE 16.-Properties of selected aldehydes and kefo'Ms

C<>mbustlbl• Formula M

A""ta.ldt• h.r..de. .. • . .. CllaCHO .. ff.O.~ Proplonal hyde. . c,n,cno .... - MI. OR l'o.ralrlehyde ........ <<"Hac no/' ·-·· 132.16 At't'lonr CllaCOCI , &ii.G8 M•thylrthyl krtone. I CllaCoc,-.;, __ · n.1o Mrthyl ~rrpyl krtonr ClloCOCalh . R6. 13 lllrthyl rlon.o c,n,coc,n,_ .. R6. 18 Methyl butyl ketonr 1 cn,roc,H, _ I 100.1e 1

I Cool ftamo•b: u_..-oo vol pet. I Cool ftllll1n: tr,.•17 vol pllt. I Ct.lcU)at'ld VII)Ue. 'I•I!OOC, • 1•100° c.

t1&~) c .. In air

(vol pet)

--~

I 62 7. 73 2.01 4.117 4. '!II 2. 72 2. 01

41171 2. 4U 3 61 2. V7 2.110 2. 'J7 I 290 346 2. 40

Lower l!mlt lu air Upper limit In lllr Ne~ AH,

<¥>1: ( Kl'Al)

mole L11 Lto u. u. u (vol c~ (voi c;; (n;') Ret. pet) pet)

--~,-4_0_ 0. 62 82 (II$) •36 •. 7 1,100' ~I«)

fOQ 2. ~ .611 '17 (18) 114 2.8 420 M) .. 1.3 .48 78 (40) ·"is -····- . ~. -

403 2.6 .I 70 (98) 2.6 avo (9.'1) 1148 1.11 . 62 62 (1M) 10 2. 7 3.1!0 <'"'l W-1 1.6 .M 63 (40) 8. 2

.. ::: ,. 340 (40 liD2 161 .M 63

\

1lo>!-•s.·o <4ni 1140 '1.4 .118 64 31l0

74 FLAMMABILITY CHARACTERISTICS OF COMBUSTIBLE GASES AND VAPORS

flammable mixtures ~ ~- THf

I l.8 ~-=-:-=~-~:-::::::------------=-~~J i r-- 70.!)mole-%THF+29.5mole-%toluene - =- -...::::.;..__--:::= ai ---- ......... ~~ ~ 1.6 ~

~ ;:: <n f- 35.6 mole·% THF + 64.4 mole·% toluene

~ 1.4 --;-;;~~---.::: ________ J 8 --- ExperimeMal --- Calculated -

1.2~--~~~~--~~·~--~--~~~--~~~~~l--~~~--~~~~~--~~ 20 40 60 80 100 120 140 160 180 200

TEMP£RATURE, •c

FtotrR• 90.-Ettoot of Temperature on Lower Limita of Flammability of THF-Toluene Mixtures in Air at Atmoapherie Preeaure.

The a.uto~ition temperatures of various aldehydes and ketones in oxy~en and air at atmospheric pressure are given m appendi.'t A. In general, the AIT values are lower than those of the corresponding paraffine.

SUI.Ft.JH COMPOUNDS

The pertinent properties of sulfur compounds a.re given in table 17. In general, they ha. ve wide filWlmable ranges and relatively low igni­t.\on temperatures (appendix A).

Flammability diagrams are $iven for carbon disulfide mixed witli carbon d1oxide-air, water vapor-air (SS9) and nitrol{en-air (fig. 95) i hy­drOgen sulfide-carbon dionde-air (fig. 96); and eth_y_l mercaptan with chlorodifluoromethane and dicblorodifluorometbane in air {117) (fig. 97). Figure 95 is interesting in that it shows not only the w • ..!e flammable range of carbon disulfide in air but also the large 9uantities of inert required to prevent the formatson of 11ammable mixtures.

FUELS AND FUEL BLENDS Fuels used for propulsion, not covered in

other sections, ar~ c-onsidered here (table 18).

Ammonia and Related Compounds

This series includes ammonia (NH,), hy:dra­zine (NaiL), monomethylhydrazine (N,Ha·CII,) and unsymmetrical diroethylhydrazine (N3H:· (CH,),).

Ammonia forms flammable mixtures with s.ir and other oxidants in a variety ot concentra­tions, as noted in table 19. White (fS5) and more re(',ently, Buckley and Husa, (19) reported that, as with hydrocarbons, an increase in either temperature or pressure tends to widen the flammable range. Further, White found that the }nwer limit. flame temperature remains essentially constant with increase in initial temperature.

TABLE 11.-Properlus of 11eltcted 81djur compO'Unds

Lclw• llm1t In 8lr Upper lhD!t In air Net 4H,

Combustible l'onn\lla N (l&!l) c., <!:) (~~ u ln&lr La ~ L u. (VOl pet) (vol (1') Ret. c.; (":') Ret.

pel) c., ~)

- ---- --------- ----------H~JUUUide ......... R, ............. u.r. 1.18 12.~ If& 4.0 o.aa &a ~ « lUI l, IVO (IJ f:'~~:::::.: c ············· TG.IJ :tea 11.68 262 1.3 .XI " ( ) 60 7.7 8,400 (U)

C~H ......... 68.10 1.111 &aa m 3.9 .eo 87 <6 22 8.4 1!00 16 '"b" me ......... Ct~B ......... 02.13 2.16 t.4A 492 2.8 .ea 80 (I 4) 18 ••• litO (/4) DIIJMthyl dt ......... CH CU, ....... ti.la :ua '·" ~·--~~--~~- 2.:1 .ao tl:l (I)

I 10 t.6 ., (I)

.. - ·-

-c: Q,)

~ Q,) c. I

cv E ~

g a:: 0 Q..

~ I.&J _, al ;::::: en ::;:) al ~ 0 (.)

1.2

J<'LAMMABILI'I 'i CIU.RACTERISTICS

o Experimental points --- Calculated

Flammable mixtures

M EK, mole-percent

75

FiGURE 91.-Eifect of Liquid Composition on Lower Limits of Flammability of MEK-'roluene Mixturt-s in Air at 30° and 200° c.

713 Jt'L·AMMABILITY CHARACTERISTICS OF COMBUSTIBLE GAAES AND VAPORS

o Experimental points Calculated

Flammable mixtures

THF, mole-percent

FJouam 92.-Efl'ect of Liquid Compoeition on Lower Limite of Flammability of THF-Toluer.Je Mixtures in Air at 30° and 200° c.

FL.U04ABILI'l'Y CHARACTERISTICS 77

!C air • 100%-!C acetone-,; inert

Flammable mixtures

Frou .. 93.-Lfmlta of Flammabil­ity of Aoetone-Carbon Dioside­Air and Aoetone-Nitrogen-Air Mi:&turet~.

0

Combuattble

10 20 30 40 50 ADDED INERT, volume-percent

TABLE 18.-Propertus of selected frul8 and jtul blends

Formula SpiJ' C,,

(A1r•1) In ur ('fOI pelt)

N

UpJIII' llmlt In m N~AH•I-----r----r---~---1-----r----r----~--<!:)

Lo- Umlt In Ur

u. u. u Ref. ~: c.. (1')

-----------1---------1-----------------------------Ammonia •••.•.••••.•••.. w.ll;:.:::::::::: A~l: 0.1141 fU~ 15 o.ee 1~ ~'m • 1.1 aoo !', W'C:c:f~iftij:iraiJiie:: N.a.cu ........ .e.01 l:~ 7.n :·

7 :~ 88 ~~ --~~--- ---~~~-- :::::::: --~~--UDI)JJ111letnoa~ NeHI(CHI)s •••.. G0.10 2.08 4-W 3 .40 116 I ~~~ 10.1 .••••••. (Ill)

dlwtbylhydrulne. DlboraDe ................. BtRt. ••••••••••. :rt.fl8 .N 11.61 t78 .8 .12 to (Iff!) 81 11.6 ........ \IU) Tetrabonlle •••.••••••.••. Boll~t ........... ai.M I.IH 1.87 .t .11 10 (') ............................ .. Pentaborane ............. BoHo ............ 111.17 2.18 !1.17 1010 .u .12 12 .................................... .

l!l&Ji -~~'tii::_:::: 't~:.:l:··-~~· ••••JJ :••:: .. :.: -••t!-· •-::::; :::i.: i ::•,;:• ·:·~f•,:::!i,-11 I Oaloulated 'fUUtl. •t•IIIO" 0.

•t•100" 0.

78 FLAMMABILITY CHARACTERISTICS OF COMBUSTIBLE GASES AND VAPORS

FJOURII 94.-Lhnlte of Flarnmabll· lty_ of Methyl Ethyl Ketone (ME K) • Chlorobromemethane (CBM)-Alr, MEK-Carbon Diox­ide Dioxide-Air and MEK-Nitro­gen-Air Mixtures at 26° C and Atmospheric Pre18ure.

0

TABLE 19.-Limits of flammability of ammonia at room temperature and near atmospheric pressure

Oxidant c,, I L u Ref.

1-Air __________________ 21. 8 15 28 (167, 182)

Oxygen ___ .. ____ .. _____ 57. 1 15 79 (U6) Nitrou~ oxide _________ 40. 0 2. 2 72 (109)

Hydrazine vapor burns in the absence of an oxidtzer, so that it has no upper limit and can therefore be used as a monopropellant. The dewmposition flame yields hy<lrogen, nitrogen, and ammonia (64, 78). However, hydrazine vapor can be rendered nonflammable by addi­tion of stable diluents or inhibitors. The amo~1nt of diluent required at any temperature and pressure appears to be governed in part by thA ignition source strength. With a 0.25-inch spark gap and a 15,000-volt, 60-ma-luminous­tube transformer as the energy source, Furno, M"rtindill, and Zabetakis (68) found that the

% air= 100%-% methyl ethyl ketone-% Inert

Flammable mixtures

10 20 30 ADDED INERT, volume-percent

40 50

following quantities of hydrocarbon vapor were needed to inhibit flame propagation in a H~·inch glass tube 6 at 125° C and atmospheric pressure: 39.8 pet benzene; 35.0 pet toluene; 27.3 pet m-xylene; 23.8 pet cumene; 21.0 pet n-heptane. On this same basis, 95.3 pet air is needed to prevent flame propagation (188); thiR corresponds to a lower hmit of flammability of 4. 7 pet hydrazine ''apor. The flammable range in air at atmospheric pressure is presented graphically in figure 98, which also gives the flammable ranges of monomethylhydrazine, unsymmetrical dimethylhydrazine, and ammon­ia for comparison ($18). The flammability diagram for the system hydrazine-n-heptane­air at 125° C and atmospheric pressure is given in figure 99. These data were also obtained in a. 0~-in-::h glass tube.

A summary of the autoignition temperature data. obtained by Perlee, Imhof, and Za.betakis (166) for hydrazine, MMH, and UDMH in air and nitrogen dioxide (actually, the equilibrium

• CCliDparable l'lltlltl wtre partlaliJ obtallled ID a ~IDcb tube.

FLAMMABILITY CHARACTERISTICS 79

0

\ %air • 100%-% carbon disulfide-% inert

" ~ ,, " ''~ \~

\~ \~

fl11mmable \ \' mixtures \ \' ,,

20 40 ADDED INERT, volume-percent

80

FIG\.iRE 95.-Limits of Flammability of Carbon Disul­fide-Carbon Dioxide-Air, Carbon Dioxide-Nitrogt>n­Air Mixtures at 25° C and Atmospheric Pressure, and Carbon Disulfide-Water Vapor-Air at 100° C and Atmospheric Pressure.

50r-·-----.-------r-------------~

% air= 100%-% hydrogen sulfide:-% C02

0 40 CARBON DIOXIDE, 'Jolume-percent

FIOURE ll6.--Limit11 of Flnmmahility of Hyrlrogf'IJ Sul­fiti<'-Carbon l>ioxidt•-Air Mixture~ at 25° C and AtmOtiphcl·ic Pressure.

% air= 100%-% ethyl mercaptan-% inert

1: .. ~ !

"' E ::J

~ z ~ II.

<5 a: UJ :IE ...J >- 5 :X: t;:;

0 20 ADDED INERT, volume-percent

FrouRE 97.-Limits of Flammability of Ethyl Mercap­tan-F-12-Air and Ethyl Mercaptan-F-22-Air Mixtures at Atmospheric Pressure and 27° C.

mixture NOa~NOa+N20.) is given in figure 100; short horizontal lines indicate the un­certainty in N02* concentrations. These ma­terials 'may i~nite spontaneously at room temperature wtth relatively small N02* con­centrations in the air; at 25° C, liquid UDMH ignites in N02*-air atmospheres that contain more than about 8 volume-percent N02*; MMH and hydrazine ignite in atmospheres that contain more than about 11 and 14 volume­percent N02*, res:pectively. In general, even smaller concentratiOns of N02* produce spon­taneous i~nition of these combustibles at higher initial combustible liquid temperatures. The effect of the hydrazine liquid temperature on the spontaneous ignition temperature in N 02 *-air atmospheres is illustrated in figure 101. Similar data are_giYen in figures 102 c.nd 103 for MMH and UDMH; there is an ~apparent anomalv in the data obtained with M.MH at 36°, 55 15 , and 67° C.

The use of various helium-oxygen atmos­pheres in place of air r11sults in the spontanenus Ignition temperature curves given in figure 104 for UDMH. Comparison of curve B of this set with curve A of figure 100 indic!ltf.ls that the s~ntaneuus ignition temperature of UDMH in N 02 *-He-03 atmospheres is the same as that obtained in NO~"'-atr at.mospheres.

Ignition tempern.ture dnta obtaint-d with UDMH in NO~"'-airmixturesat 15 and 45 psia are summarized in figure 105. These indicate that although the sl?ontarwous ignition tem­perature of UD :\f H m air is not affected ap-

80 FLAMMABILITY CHAitACTERIBTICS OF COMBUSTIBLE GASES AND VAPORS

Fxoun11 98.-Limitll ot Flamma­biJ!t~ of Ammonia UD.MH, MMH, and Hydrazine at At­m~herio Pre&llure in Saturated and Near-Saturated Vapor·Air Mixturea.

.. LaJ 0:: ;:) CJ) (/) UJ a: c. ...J c:r .... 0:::

~ 20

Upper limit

Flammable mixtures

Cst

Lower limit

100 78.9 -c • u

~ • Q. I • 26.3 E

:::s 0 > ..

13.2 0:: 0 c. c:r

7.9 > UJ

5.3 ...J m 1-(/) ::) m 2 0 u

1.3 200

FLAMMABILITY CHARACTERISTICS

100

KEY o Flammable x Nonflammable

HEPTANE-VAPOR, volume-percent

FIGURE 99.-Flammable Mixture Compositions of Hydrazine-Heptane-Air at 125° C and Approximately Atmospheric Pressure.

81

82 FLAMMABILrrY CHARAC'l'E.iUST!GIS OF COMBUSTIBLE G.~SES AND VAPORS

200

0

a UOMH b MMH ~ Hydrazine

Reaion of spontaneous ianition

Dew point line of NO~~ ----____ ... ---

10

---NOt CONCENTRATION, volurne.percen~

30

FJCURE 100.-Minimum Spontaneous Ignition Tem­peratures of Liquid Hydra?Jinc, MMU, and UDMH at an lnitinl Tempcratul'e of 2i° C in Contact With N01*-Air Mixtures at 740 ± 10 mm Hg as a Function of N01• Concentration.

preciably by this pressure change, it is affected m a range of N02•-air mi.;{tures.

The data presented in figures 100 to 105 were obtained with liquid fuel in contact with ~'apo:r­ized NO: ~n air. Similar data obtained with vaporized UDMH-o.ir in contact with NO; are given in fi~ure 106. This figure indica.tes that UDMH-atr mixtures that oontn.in more than 9 volumewpercent UDMH will ignite spon­tanoously on contact with NO:; UDMH-air mixtures that contain more than approximately 2 volume-percent UDMH can be Ignited by an ignition source under the same conditions (166).

Boron Hydrides

This saries includes diborane (B2H~), tetm­borane (BcH,o), pentaborane (llaltG), nnd deca­boraae (B,oHI4). However, relittble upper und lower limit data are a vuilable only on the first member of this series ut the present tillle. These were obtained by P1trker und W<.•lfhnrd (163) who determined the limits of flnmmability of diborane in air in a 5-cm-diameter tube ut an initial r>ressure of 300 mm Hg; this combustible forms flammable mixtures in air in the rnnge from 0.8 to 87.5 volume-percent. A pale bh.i.e flame propagated throughout the tube .ul, the upper lim1t; luminous 1hunt~s were not visible above 79 vol•1mewperccnt. Limit of flammu­bility curves for the system dibor11 ne-ethane-air are presented in rectangular coordinates in figure 107. ~~xceP.t for the slight dip to the ethhne­axis (zero dtborane) in the area in which etLane forms flammable mixtures in air, these curves are rather similar to those obtained with other combustiblewOxidant-inert systarns. Burning velocities in excess of 500 cm/l'lec were measured in this same study Cor fuel-rkh diborane-air mixtures.

Berl and Renich have prepared a summnry report about boron hydrides (9). It includes data obtained by these and other authors; they found the lower limit of penta.borane in air to bo 0.~2 volume-~ercent.

The autoignitwn temperature of diborane in air is aypa.rently quite low. Price obtained a value o 135° C at 16.1 mm Hg (169); that of pentaborane is 30° Cat about 8 mm Hg (9).

Ga.solines, Diesel and Jet Fuels

Fuels considered in this section are blends that contain a wide variety of hydrocarbons and additives. Accordingly, their flammability characteristics aro governed by the method used to extract a vapor sample as well as by the history of the liquid. For example, since the lower limit of flammability, expressed in volumewpercent, is inversely proportional to the molecular weight of the combustible vap<>r, equation (28), the first vapors to come from a blend, such as gasoline, give a higher lower limit value than the completely vapori.t.ed sample. Conversely, the heavy fractions or residue give a smaller lower limit value. For this reason, there is some disagreement about the limits of flammability of blends such as gasoline and the diesfll and jet fuels. These fuels are, in general, characterized by a wide distillation range; the ASTM distille.tion curves

P'LAMMABXLITY CHARACTERISTICS 83

Region of spontaneous ignition

0

NO~ CONCENTRATION, volume-percent

FIGURE 101.-Minimum Spontnnrous Ignition Tempemtnres of Liqnid Il~·drnzine ut Various lnitial Tl,mpt'ratures in ~01*-Air Mixtures at 740± 10 mm llg as a Fuurtion of NO,• Concentrution.

84 Fl.A:\1:\IABILITY C'HAHACTEIH8TJC8 OF COMBl'8TtBLE GA8E8 A~D VAPORS

200

P ss• . ..__ uJ 0:: :;)

< 100 0:: w Q,,

:e w 1-

·--·--~--···- __ T ... _ ....... --r-·-----~----r----r-----·l

Regi0n of spontaneous ignition

NO~ CONCENTRATION, volume-percent

I l

I

FwntE ](fl ... ~liuirnum 1-'pontllll<'OII>' l~!;llition TPmpPmtur<'"' of Li<1<ti< 1 \1 :\III at \'ariotJH Initial T•·lltpt·r Jt:u·,., ill :\02•-Air :\lixturt•s nt 740: 10 111111 ilg a:; a Fuuct.io11 of :\02* ( 'oul'l'l•tralioto.

FLAMMABILITY CHARACTERISTICS 85

Region of spontaneous ignition

0 5 10 20

NO~ CONCENTRATiON, volume-percent

F!Gt:RE 103.-!\finimum Rpontnneous J~nition TPmpPratur!'s of Liquid l"D\fH at Various Initial Temperatures in X03*-Air MixturP!l at i40 _;~ 10 mm llg as a }'unction of .X03* Concentration.

86 FLAMMABILI'I'Y CHAHACTEHISTICS OF COMBUSTIBI,~; GASES AND VAPOHS

FIGURE 104.-Minimum Spon­taneous Ignition Temperatures of 0.05 cc of Liquid UDMH in H~OrN01• Atmospheres at 1 Atmosphere for Various He/02 Ratios.

p LL.i' 0:: ::I

~ 200 a:: w Q..

:::E w .....

0

Curve He/02 (J 0.0/100 b 100/25 c 100/6.50 d 100/1.70 tl 100/0.30 f 100/0.00

Region of spontaneous ignition

o,b

5 10 1'5 20 NO~ CONCENTRATION, volume-percent

25

FLAMMABILITY CHARACTERISTial 87

300 ---- -- -- 1 - --------r----T-------

200

100

0

11 15 psia b 45 psia

Regio" o~ spontaneous ignition

5 10 15 NO~ CONCENTRATION, volume-percent

20

FIGURE 105.-Minimum Spontaneous Ignition Tem­peraturet of 0.05 cc of Liquid UDMH in N01*-Air Mixtures at 15 and 45 Psia as a Function of N01* Concentration.

of two gasolines and three jet fuels considered here are given in figure 108. Unfortunately, such curves give only an approximate measure of the volatile constituents in the liquid blend. Even relatively nonvolatile high-flashpoint, oils may liberate flammable vapor8 at such a slow rate that the closed vapor space above the liquid may be made flammable at reduced temperatures. Gasolines can produce flam­mable saturated vapor-air mixture at tempera­! ures below -65° C (241), although the flash points of such fuels are com•idered to be about -45° C (158). An apparent discrepancy thus exists if flashpoint data are used to predict the lowest temperature at which flammable mixtures can be formed in a closed vapor space above a blend in long-term storage.

As noted earlier, the limits of flammability of hydrocarbon fuels are not strongly dependent on molecular weight when the limits are ex­pressed by weight. However, since results measured by a volume ttre!erhaps more widely used than those measure by weight, typical flamme.bility curves are presented by volume for the li~ht fractions from aviation gasoline, grade 115/145 (fig. 109), and aviation jet fuel,

200

~) 150 w 0:: ~

i ~ ~ UJ

~- 100

50

0

Re,gion of spontaneous ;gnition

l Lower limit of flammability I

of UDMH in air ~

.... -.... -- j Dew point line

of UDMH ........ -­---

4 8 12 20 UDMH CONCENTRATION, volume-percent

FIGURE 106.-l\linimum Spontaneous Ignition Tem­peratures of Vaporized UDMH-Air MixturM in Con­tact With 100 pet NO; at 25° C llnd 740± 10 mm Hg as a I- unction of UDMH Concentration in Air.

grade JP--4 (fig. 110). Combustible vapor-air­carbon dioxide and vapor-air-nitrogen mixtures at about 25° C and atmospheric pressure are considered for each. Similar data are given in figure 14 for the gasoline vapor-air-water vapor system at 21° and 100° C; the effect of pressure on limits of flammability of volatile constituents of JP--4 vapor in air are discussed in connection with fi~ure 12.

l\Iimmum autoignition temperatures of gaso­lines and jet fuels considered here are given in compilutions by Zabetakis, Kuchta, and co­wo:-kers (126, 237). These data are included in table 20.

Setchkin (194) determined the AIT values of four diesel fuels with cetune numhers of 41, 55, 60 and 68. These data are included in table 20. Johnson, Crellin, and Carhart (92, 93) obtained values that. were larger than those obtained by Setchkin, using a smRiler apparatus.

88 FI..AMMAI:ULITT CHARACTERIB'l'ICS OF COMBUS1'1BLI: GASES AND VAPORS

100

!lair .. 1~-!IJ; cilborane-" lth-

20

_L_•I (drlxnM) ______ , __ _ 0 20

Frouu 107.-Limitas of Flammability Ethane-Air Mixtures at Labl)ratory and 300 mm Hg Initial Presaure.

of Diborane­Temperatures

~~--~~--~~--~------T---n~

20 40 60 80 100 DISTILLED, percent

FruuRE 108.-ASTI\1 Distillation Curves for, A, Avia­tion Gasoline, Grade 100/130; B, Aviation Gasolint•, Grade 115/145; C, Aviation Jet Fuel, Grad1! .JP-1; D, Aviation Jet Fuel, Grade JP-3; and E, Aviation Jet Fuel, Grade JP-·4.

I I ;

0

"air • 100•-• psollne-• Inert

Flammable mbdum

10 20 30 ADDED INERT, volum•p.rcent

50

Frouu 109.-Limitas of Flammability of Aviation Ouollnel Oradee 115/145 Vapor.Carbon Dioxide-Air and 1lli 145 Vapor-Nitrogen-Air, at 27° C and At­mospheric Pre~~ure.

lOr-----~-------~-----r------~-----.

!I air • 100%- !I JP-4 -% Inert

0 10 20 ADDED INEtll, volume· percent

FroUJu: 110.-Limite of Flammahility of JP-4 Vapor­Carbon Dioxida-Air and JP-4 Vapor-Nitrogen-Air Mixtures at 27° C and Atmospheric Pressure.

TABLE 20.-Autoignition temperature IK.£lues of various fuels in air at 1 atmoHphere

Fuel: Aviation guo line: A IT, •c

100/130............................ 440 116/146 ••..... _____________________ 471 Aviation jf.'t fuel:

J J>-1 _. ___ • _ •••••• __ ••• _ ••• __ .• _ • • • 22R J J>-3 .... _. ___ . _ . _ . _ • __ . _ • _ _ 23R JP-4. __ . _. _. _ ... _. _____ . _. _ 242 Jl'-6 ... -- .. -------.-.- ". -. -- -.---- 232

Dins1•l ful'l: 41 cl'!anl' ________ . _ _ _ .. _ . _ _ . - .. - - 233 51) ('1'1.8111' -- . . - . - .. - - --- 230 6() Cllt.&lll' __ . _ •. _ _ _. 225 68 cctane. _ .. __ .. ___ . _ . - - . __ .. • . . . . 226

FLAMMAHILITY CHARACTERISTICS 89

Burnin~ v-elocities of the fuels consirlered here are m the same range as those o( the hydrocarbons considered earlier. Values for various fuels have been tabulated by Barnett and Hibbard (166).

Hydroqen N umerou!l flammability cha.ract.eristics

studies have been conducted with hydrogen in recent :rears. Drell and Belles have prepared an excellent survey of these characteristics (48). This survey includes all but the most recent work of interest.

The low pressure limits of Baroe propagatinn for st:lichiometric hydrogen-air mixtures are somewhat lower than those for stoichiometric ethylene-air mixtures (1 97) in cylindrical tubes. In the ran~e from 6 to 130 mm Hg, the limit for stoichwmetric hydrogen-air mixturoA is given by thE' expression:

log P=3.19-1.19 log D, (57) where P is the low-pressure limit in millimeters of Hg, and D is the tube diameter in milli­meters.

H;ydrogen forms flammable mixtures at amb1ent temperature<~ and pressures with oxy­f~! air, chlorine, and the oxides of nitr(lgen.

its of flammability in these oxidants at approximat\'lly 25° C and 1 atmosphere are listed in table 21.

TABLE 21 -Limits of jla.mmabi.J:ity of hydrogen in various oxidants at 25° G and atmosplwric pressure

Ref. Oxidant I Oxygen- .. - --- .. - _- ___ -~--4.·-0-l---9-5 -l- .. --(40;

~k~<>;in_e_-_~=~===:===~=, !: ~ ~S I <etfJ, J;~j N.o. ____ .. _ _ _ _ _ _ _ _ _ _ _ a. o 84 (189) NO__________________ 6. 6 I 66 (189)

Flammability dia~ams of the sy3t.ems hvdro­gen-air-carbon diox1de and hydrogen-air-nitro­gen obtained by Jones and Perrott (112) ar£l briven in figure Ill. Lines that establish minimum oxygen values for each system are also included. 1'\ ote that although the lnini­mum value occurs near the "nos1'" of the hydrogen-a.ir-nitrogen eurve, the corr1•sponding value occurs at the upper limit of the hydrogen­air-carbon dioxide curve.

Flammability dia.grams obtained by Scott, Van Dolah, and Zabetakis for the systems hy:drogen-nitric oxide-nitrous oxide, hydrogen­mtrous oxide-air, and hydrogen-nitric oxide-air aregivenin figures 112-114 (189). Upper limit

I i 40 z

I ~

20

0

--~

~air • 100%-% hydrogen-% inort

MinO~".. 5.2% ..,_,

Flammable mixtures

20

""' "'"' ' MtnO~ 5.0%

AO[JEO INERT, volume·perr.ent

Fwvax 111.-Limit! of Flammability of Hydrogen­Carbon Dioxide-Air and Hydrogen-Nitrogen-Air Mixtures at 25° C and Atmospheric PreiiiiUre.

curves were found to deviate fr(JID the results obtained from the Le Chatelier law, broken curves; additional data are given in the original article.

The burning velocity of hydrogen in air at 25 ° C and one atmosphere range from a low of a few centim~:~ters per second to 325 em/sec (68). When liquefied, it. vaporizes and burns in air at r~ rate that is determined by the rate at which heat enters the liquid. Heat is a.b~Jtracted from the surroundings and, where a flame exists, from the flame itseH. Figure 115 gives the results obtained from vaporizing liquid hydrogen from paraffin cast in a Dewar tlask; experimental pomts were obtained from gas evolution measurements. The solid ~;urve (theoretical) was obtained by Zabetakis and Burgess by assuming the heat influx rate to be conduction limited (234); the initial flash vaporization rates are probably film- and nucleate boiling-limittJd. The theoretical liquid regression rates following spillage of liquid hydrogen onto three soils are presented in figure 116, the corresponding decrease in liquid }eye} is given in figure 117. Be<' a use of its low temperature, the v11porized hydrogen forms a vapor trail 1\ii it. leaves the liquid. However, tlie position of this trail or visiblfl doud does not necessarilv coincide with that of the tlarnmable zones formed ubove the liqui~ pool. This is illustrated in figure 118, in which the positions of the flummable zones und visible clouds are defined in u height-elupsed time graph. Two flammable zones are defined here. These are ruso seen in t.he motion picture sequence (fig. 11 9) of the visible cloud.c and

90 FLAMMABILITY CHARACTERISTICS OF COMBUSTibLE GASES AND VAPORS

KEY • Flammable mixture o Nonflammable mixture

FtouRII: 112.-Limit.s of Flammability of HrNo.•,;,o at Approximately 28° C anrl 1 Atmosphere.

KEY • Flammable mixture o Nonflammable mixture • Coward and Jones,

Bureau of Mines Bull. 503

0 Smith and Linnett, JCS (London), 1953, pp. 37 ·43

• ~.<AMMABILITY CHARACTERISTICS

~ 60 /------~f-------J..40 ~ ~ . ~ %

fl ~ ~ ~ 0 ~ ~ ~ ~ ~ ~ ro

FIGURE 113.-Limits of Flammability of 111-::\' 20-Air at Approximately 28° C and 1 Atmosphere.

91

92 FLA~.fMABILITY CHARACTERISTICS OF COMBUSTIBLE OASES AND VAPORS

KEY • Flammable mixture o Nonflammable mixture • Coward and Jones,

Bureau of Mines Bull.503

FIGURE 114.-Limita of Flammability of HrNO-Air at Approximately 28° C and 1 Atmosphere.

FLAMMABILITY CHARACTERISTICS 93

Start of liquid transfer to Dewar --,---r--~--~-,---T--~--~~r--T--~--~--r-~--,

\ \ I \ I \ I \ I ~ ~0 I '\~ I "

Re1!on f of violent

bollln1 J--- Quiet vaporization

FIGURE 115.-Rate of Vaporization of Li({uid Hydrogen From Para~n in a 2.8-lnch Dewar F'lask: Initial Liquid Depth-6. 7 Inches.

1

~ .2 .5 ·:.\

~--~--~--~--~----._--~'---·--~--~--~--~--~~--~--~--~~~--~ 60 100 120 140 160 ELAPSED TIME, seconds

FIOIJRI: 116.-ThooreticRI Liquid Heltl"eBSion Hntt>& Following Spillage of Liquid Hydrogen Onto, A, an Anrage Soil; B, Moist Bandy .Soil (8 Pet. Moisture); and C, Dry Saully Soil.

94 FLAMMAB lLITY CHA ~-~ ~- i\At'TERISTlCS OJ<' COMB -,---1-f USTIBLE OA ' ---r--- SES AND V" -r--T- -,-- ~~ons

FIGUilll 118 ~~~ Mixt-;-!x~nJ of Flamma-Rap~~e S Cloud For: eight of Liquid ~illage of 3 t After adam sJFn on 8 D;yte~ of Air At aoe in a Q ac-mOBphere at 16o ~~cent

7

FI.AMMABil.JTY CHARACTERISTICS 95

fiiiJiles that resulted following spillage of 7.8 liters of liquid hydrogen and subsequont ignition of vapors above the spill area. The heisht and width of firebnlls that resulted from i~mt.ion of vapors produced bv rapid vaporiza­tlOU of about 3 to 90 litera olliquid hydrogen are given in figure 120. The data are repre­sented fairly well by the equation

Hmu.= Wmu=7-v'''fl fet~t= 17.8-v'M feet, (56)

where Hmu and lVmax are the maximum flame hei~ht and width, respect.ively, v. is the volume of hq,uid hydro~en in liters, and M is the mass of th1s volume m pounds.

The burnin~ rat.e of a 6-inch pool of liquid hydrogen in air is given as the regressi()n of the liquid level in figure 121 i burning rate data for liquid methane are included for comparison. AD extrapolated ·value of burning rate fol' large pools of liquid hydrogen is included in fi~ure 52.

Approximate quantity-distance relationships can oo established for the storage of liquid hy­d=ogen near inhabited buildings and other stor­age sitfls ;f r-ertain assumptions are made (SS, 160, 234). Additional wurk is required to establish such distances for very large quantities of liquid.

The detonation velocity and the static and :reflected pressures devAlupod by a detonation wave propagating through hydrogen-oxygen mixtures are given in figure i6. The predeto­nation distance in horizont&.l pipes is reportedly proportional to the square root of the pipe diameter (229) ; this is presumably applicable to results obtained with a mild igmtion source, sinc.e a shock front can establish a detonation at essentially zero run up distance. Numerous investigators have examined this and related problems in recent years (11--13, 65, 196-137, 161).

HYDRAULIC FLUIDS AND ENGINE OILS

Both mineral oil derived and synthetic hy­draulic fluids and engine oils are presently m common use (148). These materials are often used at elevated temperatures and pre;:;sw·es and contain additives designed to improve 'ita­bility, viscosity, load-bearing characteristics, etc. Such additives affect flammability char­acteristics of the base f!uid. However, the base

FIGtlRE 119.-Motion Picture Sequence (16 Frames per Second) of Visible Cloud8 and :Flames Reeultmg From Rapid Spillage of 7.8 Liters of Liquid Hydrogen on a Gravel Surface at 18° C. Ignition Source: 20 Inchea Above Gravel.

96 FLAl\fMABILJ1'Y ClUHACTERISTICS OF COl\ISVSTIBL~ GA8t:~:. A~W VAPJR,3

F'lounE 120.-!\fn'l:imurn uanw hPight and widt •. pwd·•c<'d by lgnit.ioh cf vapor-air mixtures formlld by sudden spillage of ~.S to 89 Htcl"ll e>f liquid hy­dl·ogeu (V1).

F'IUURE 121.-Burning rates of liquid hydrogen !l.nd of liquid methane at tbe boiling points in fl-inch-Pyrex Dewar tiask.s.

~ l:r--r~·-.,.,.,.,.,----r ·---.-.---.--en 60 • Flame height ~ o Flame w1dth

~ 40 :I 0 :I i 20

i

5

~ .&. u

4 .5 -..I

~ ...J

0 3 Q ...J ~ 0 z 0 ii'! U) lol 0:: C!l LIJ 0::

v,, liters

'Methane

20 30 40 50 ELAP5ED TIME, rnii"HJtes

60

:\i'LAM.MAl'IILITY C.H.AftACTERIS'.riCS 97

fluid generally plays a predomimmt role iu de­termining limits of flammability "ind ignition t<~mpArt\tur~ of a particultU' flutd. For exam­ple, m.uny of the oil-based fluids have io\\•er limits of flammability that fall in the rangt>"' given in figure 22 for par!lfiin hydrocarbons. I<'urtlwr, those that have mir1imum autoignition temperatures in tb.e ltlWCr t.emjleruture ranges cousiclered in tiugr~s 43 and 71 are nut affected tlppn,ciably by oxygen conc~mtratiou of the »tlno1;phere and by ambient and fluicl.-injec·i~lll pressu&-e&; those t!Ja.t. havfl minimum autoigni­tion tempm·ttt'U'es in the hi~ht.~r temperature runges do not follow these ~emir~>.lizations (237). Sirwe these fluids are des1gned for use at ele­vated temperatures awi :pressures, they ru'e nor­mally made up of high ·molecular weigh~ mate­tinls. Accordmgly, they are flammable at ordinary tempex·atures and pressU!'es' as mists and Coams. Hw-goym~ u11d his coworkers (27) found that. luhricating-oii. mist,., were flt...mma­b!P in air but. not in carbon dioxide-air mix­ture.: that contained about 2g '¥nlume-percent carbon dioxide (fig. ao). At elevated temper­llturr~, the •Jil vapors crRcked Rlld produced aePtylene llnd hydrogen, which a:tfecteO. the fl!!.rnn1abilit.y of thl'l resultant mixture; the va­porH are often unstable at elevated tempera­tures. Cbiantella, Affens nnd Johnson have <kt~rmined the effect of eievnted temperatt'.l'es on the stability and ignition prollerties of thret~ commNcial tnaryl phospha ie ftmds (86).

Zabetakis, Scott, and Kennedy have deter­mbed the effect of pres~nre on the autoignition temperatures uf commercial lubricants ~248). Figure 122 gives the mir.imum autoignition temperatur~ for four commercial phosphate ester-base fluids (<''li'Ves 1-4) and three mineral oils (curves 5-7). In each case, the minimum autoignition temperature was found to decretl.8e with increase in pressure over most of the pressure ran~e considered. A plot of the logarithm of the imtial pressure to temperttture ratio versus the reciprocal of the temperature is given for curves 1 to 7 in figure 123. The resultant curves are linear over I' limited tem­perature rttnge.

The ratio of the final temperature attained by air in an adiabatic compression process to the initial temperat.ure is given in fi~ure 124 as a. function of both the final-to-imtial pressure ratio and initial-to-final volume ratio. If a lubricating oil is exposed to high temperatures during a compression process, autoi~nition may occm if the residence or contact tlme is ade­quate. Such high temporatures do occur in pra.rtice and have been known to cause disa.s­trow~ explosions (58, 146, 149, 227, 291). The curves iu tigtu-e 125 show that in the compression pressure range 1 to 10 atmospheres (initial pre."sure::= 1 atmosphere), a wide range of

ambient ~~mperaturas can lead to the auto­i.gnition oi 11. mineral oil lubricant (curve 5) if ii'Ufticient vapo~ or mist is in the system. In the same pressure range, only elevated initial. t.emperatt;rcs coul':l lead to the a.utoi~nition of a pbosphttttl ~tar (curve 4). If the initial pressure 1s i.r.creiiSed to 10 atmospheres, u.utoignition cnn oo·~ur at, lo?!er air-intake temperatures in tlVery CMe (248).

MiSCELLANEOUS The tfammability characteristics of a number

uf miscellaneous combustibles not considered elsewhere, are discussed in this section. These include ~:arbon monoxide, n-prop,Yl nitrate, and t.he halogenated hydrocarbons. The properties of these and a great variety of other materials 11re included in Appendix A.

The limits of flammability of the systems car­bon mo::1oxide-carbon dioxide-air and carbon monoxide-nitrogen-air are presented in figure 126. These curves were constructed (rom the flammability data obtained by Jones in a 2-inch vertical glass tube with upward flame propaga­tion (112); other representat.ions may be found in the original reference and in the compilation prepared by Coward and Jones (40).

Materials that are oxidized or decomposed readily may yield erratic flammability data under certain conditions. This effect lS illus­trated in figure 127 which summarizes the lower-limits data obtained by Zabetakis, Mason and Van Dolah with n-propyl nitrate (NPN) in air at various temperatures and pressures (248). An increase in temperature from 75° to 125° C is accompanied by a. decrease in the lower-limit values; a. further increase in temperature to 150° c results in a rurther lowering of the lower limit a.t pressures below 100 psig, but not at the higher pressures. An increase in the tempera­ture to 170° C results in an apparent increase in the lower·limit value because of the slow oxida­tion of NPN. A complete flammability dia­gram hilS been constructed for the NPN vapor system in figure ~2~; a single lowe~ limit curve and two upper llimt curves are gt.ven here tc show the effect of pressure on the flammable ral}ge of a vapor-air system.

The spontaneous ignition of N PN in air was considered earlier at 1 ,000 psig (figs. 3, 4). The explosion pressw-es obtained at this initial pres­sare in air and in a 10 volume-percent oxygen +90-volume-percent nitrogen atmosphere at various NPN concentrations are presented in figure 129. A summary of the minimum spon­taneous ignition and decomposition tempera­tures obtained with NPN in air and nitrogen respectively are given in figure 130. The data given in this figure exhibit a behavior that is typical of that found with other combustibles

98

6150

~600-...; ~550 1-

~500 L&J 0.

~450 1-

~400 i= z350 t!)

0 ~300 ~

:I 250 i ~200 :I

FLAMMABILITY CHAHACTElUS'riCS OF COMBU!STTHLF. GASES A;>;D 'l."AP0US

Region of autoignition

150~~------~--~~~~~~~----~~--~~_.~.~~~----~2~0~0--~ 2 4 6 8 10 20 40 60 80 100 INITIAL PRESSURE, otm

·1

FIGURE 122.-Variation in Minimum Autoi;;;nition Temperature With l'n·s~llrt' of Cornnwrcia! Phosphate Ester and Mineral Oil Lubricants in Air in tL 4.'>0-cc-Stu!ult•ss Steel BomiJ.

F1ouaz 123.-L<:>garithm of lni­tbl f'r.,..eur2-AIT Rat1o of Seven Fluids in .Air for Various Reciproclll Temperature&. Data !rofl'l Figure 122.

FLAMMABILrl'Y CH.ARACTERIS'riCB

:If! • ..... E '6

.00

R5QIOII of outoiQnitlon

99

1()() FLAMMABILITY CHARACTERISTICS OF COMBUSTIBLE GASES AND VAPORS

Ftotru 124.-Variation in Tr/T; of Air With V,fVt and With P,/P; in an Adiabatic Com­PreiiJion Proceee.

V,· P,

v, P,·

FIGURE 125.-Variation In Air Temperature With PdP; in an Adiabatic Comrression Procesc for Five Ivitia Air Tempera­tu:res (0°, 25°, 50°, 75°, and 100° C). Regions of autoigni­tion for lubricants IV and V at Pr/P, Btltween 1 and 10 Atmos­phere and P1 of Between 1 and 10 Atmospheres.

FL.~BILITY CHARACTERISTICS

Rer'ion of autoignition

101

10

102 FLAMMABILITY CHARACTERIEITICS OF COMBUSTIBLE OASES AND VAPORS

80..---~

0 20 40 60 80 ADDED INERT, volume-percent

Froue 126.-Limits of Flammability of Carbon Mo­D01ttde-Carbon Dioxide-Air and Carbon Monoxide­Nitrogen-Air Mixtures at Atmospheric Presoure and 26" c.

,._ 4 ~ .... ~

I

at elevated pressures; the minimum spontaneous i~ition temperature first decreases .with ini­tta.l increase in pressure and then increases as the pressure is increased still further (110, B48).

Burning Vl~locities were found to range from 20 em/sec to 110 em/sec in NPN-air mixtures cont.aining 3.0 to 7.2 volume-percent NPN. Detonations were obtained in saturated NPN vapor-air mixtures from 30° to 65° C e.nd 1 atmosphere pressure; the detonation velocity was from 1,500 to 2,000 meters per second. Stable detonations were obtained with liquid NPN at 90° C; the detonation velocity was from 4,700 to 5,100 meters per second.

Although many of the halogenated hydro­carbons are known to be flammable (40) still others such as methyl bromide, methylene chloride, and trichloroethylene (TCE) have been considered to be nonflammable or esstmtial­ly nonflammable in air. As noted in connection with the methyl bromide data given in figure 28, Hill found methyl bromide to be flammable in air at 1 atmosphere pressure (84); the re­ported limits of flammability were from 10 to

~ 3 Flammable mixtures "5 >_ (L 0 2 r:l. <[ :>

~ a. z

0 100 200 300 400 500 600 700 800 900 1,000 PRESSURE, psig

FIGt'RE 127.-Lower J.iudt~ of Fl11mmability of :'\J>:'\ Vupor-Air :\I ixturps Ov"r tlw l'r"s~ur" Han~,~,. I· rom 0 to 1,000 Psi~o: at 75", 1:.!5°, 150°, 1111d 170'' ( ',

FLAMMABILITY CHARACTERISTICS 103

a:

~ z 0.. z

90 --

80 -

70 -

60 -

50 -

40

20 -

10 1

Impossible vopor- air mixtures ot T 6125 •c

Saturated vapor-air mi~ttures T = 125°C

\ -T•5o•c <('

' ... flammable

0 200 400 600 BOO 1,000 PRESSURE, psig

FrouRE 128.-Flammahle ~p~ Vapor-Air :\fixtures Form<>rl On•r the l'rPssurc Hauge From 0 to 1,000 Psig at 50° and 125° C.

15 volume-percent methyl bromide. At an initial pressure of 100 psig, the flammable range was found to extend from 6 to 25 volume-per­cent. Similarly, methylene chloride and tri­chloroethane wel'e found to be flammable in air at ambient temperatures although the flam­mable ranges were not determined. In general, much higher source energies are required with t.hese combustibles than are required to ignite methane-air mixtur~.

An approximate flammability diagram was prepared by Scott for trichloroethylene-air mixtures (190); a modification is reproduced in .figure 131. The lower limit data were obtained in a vertical 7-incb-diameter ftammabil,ity tube and the upper limit data in an 8-in'ch-diameter glu.ss sphere with upward propagation of flame. ~'lammable mixtures of TCE and air were also obtained between 10.5 and 41 volume-percent TOE at. 1 atmosphere and 100° C in an 8-inch­diameter glass sphere. Under the same con­ditions, flammable mixtures of TCE and oxygen were obtained between 7.5 and 90 volume-percent TCE. However, additional work must be conducted with this and the other halogenated hydrocarbons to determine the effect ot vessel size, ignition source strength, temperature and pressure on their flammability chftJ'acteris tics.

Other useful flammability data may be found for various miscellaneous combustibles in many of the publications listed in the bibliography (40, 154, 200, 208-214, 218). These include data on the gases produced when metals react with water (56) and sulfur reacts with various hydrocarbons (62). Still other references con­sider the hazards associated with the production of unstable peroxides (142, 157, 187, 288) .tnd other reactive materials (66, 74, 80, 189).

104

5,000

.i' Ill a.

"" a:: :::> (f) (f)

"" a:: Q..

z 0 (f)

0 -I Q.. )(

"" 0

FLAMMABILITY CHARACTERISTICS OF COMBUSTIBLE GASES AND VAPORS

0

0.3 0.6 0.9 1.2

Oxidant 0-- Air c--10% 02 + 90% Nz

1.5 1.8

NPN VAPOR, volume-percent

2.1

Flouam 129.-Variation of Explosion Pressure Following Spontaneous Ignition With NPN Concentration, Initial Pressure 1,000 Psig.

Fzouu 130.-Minlmum Spontanoous Ignition and Decomposition Temperatures of n-Propyl !'litrate in Air as a Function of Pl'eiiii•Jrt!, Type 347 Stainless Steel Test Chamber.

0 10 ..------------,

Impossible mixtures

]/ 0

I 50

FLAMMABILITY CHARACTERISTICS

TEMPERATURE, •c

Flammable mixtures

/ Lower Iiili it

Nonfllmmable mixtures

I 100

T[MPERATURE, 'F

I !50

FIGURE 131.--Flammability of Trichloroethylene-Air Mixtures.

I 200 250

105

ACKNOWLEDGMENTS Many of the unpublished data reported here

were obtained by the predecessor of the author, the late G. W. Jones, former chief of the gas explosions branch. Other data were obtained by the author and his coworkers, particularly Messrs. George S. Scott, Joseph M. Kuchta, Aldo L. Furno and Henry E. Perlee. In addition, the author is indebted to Drs. David

106

Burgess 6 and Robert W. Van Dolah for many fruitful discussions of the material contained in the sections on Definitions and Theory, De­fiagration and Detonation Processes, a.nd Pre­ventive Measures.

• Presently wltb Reaction Motors Division, 'rhlokol Chemical Corpo­ration, Denville, New Jersey.

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, 1! t,\ II• ld'\ ( · H:tl'lrt 1• ,·tnd H·•'· ··t H. flu•hanl. I~~.-,-;-, ·.! ... t'l JtP

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220.

221.

222.

223.

224.

225.

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228.

229.

230.

231.

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APPENDIX A TAFLE A-1. Summary of limits of flammability,

lower temperature limits (TL), a.nd mim:mum autoiynition temperatures (AIT) of indiculual gases a.nd t•apors in air at atmospheric pressnre

Combustible

Limits of flllm- \ mability (volurne-1

percent) , T,, A!T

I (o C) (o C)

_________ '-~l u,. ---------

AcetaL ......•...•.. Acetaldehyde._ .. _ . _ . Acetic acid •.. _ .. ___ _ Acetic anhydride ____ _ Acetanilide_ •... _ •. __ Acetone ____________ _ Acetophenone. _____ _ Acetylacetonc .. ____ . Acetyl chlorid~. __ ... _ Acetylene •••... _____ _ Acrolein __ . _ c .. _ • ___ _ Acrylonitrile .••• ____ _ Acetone Cyanohydrin. Adipic acid ••.....•. _ AldoL. __ •... _ . _. _ .. AllylaicohoL ______ _ Allyl amine._ .. _ Allyl bromide _______ _ Allyl chloml"- __ . ___ . o-AminudiphcnyL __ _ Ammonia ... _. _____ _ n-Amylacetate. _. n-Amyl alcohol. __ . __ tert-Amyl ah'ohoL .. __ n-Arnyl chloride tert-Amyl chloride._._ n-Arr.yl_et_hn ... ___ .

1

1

Amyl nttntP ___ ... _. __ n-Amyl propiona!!'. _ Amylrne. _ . _. _. __ . Aniline .. __ .. Anthracene ____ .. _. __ n--Amyl nitrate .. __ ... Benzene •• ____ ..... _ . Benzyl IH'nzuate ..... : Brnz~-1 chloride ..... I BicyelolwxyL .. _ .. _. _ BiphrnyL _ .......... .. 2-Bipiwnyiumil•:·.. .. _ Brornobenzen!L _. ___ _ Butadiene (l,:l) ____ _ n-Butane .•...... __ _ 1 ,3-llutandioL. . ____ _ Butene- I.. _____ . ___ . Butent'-2. __ ... _. _ .... n-Butyl acr>tnte. n-Butyl alcohol ...... _ 1er-Hutyl ah•o'Jol. __ tert-Butyl alcohoL._ teri-Butyl ami1w .... __ n-Butyl benzeue .... .

l l ~ I_ . ~~ _ _ _ _ :: !fg : i: ~ 1.8. ~?---- --- ~:- ~~g

2. 6 I 13 465

: {: ~ ! = = = = : ~ = = i = : = = =: 3~g I 5. 0 I .. _ _ .. _ • • • 390

2. 5 100 305 2. 8 31 235 3. 0 -----· - -6 2. 2 12

• 1. 6 1.-- ---- - -. - . _ _ 420

• ~: g i'"i8""' ·j -'22- 250

2. 2 22 - - - . 3'15 • 2. 7 - - - - - -- - 29.')

2. 9 _ __ _ _ _ __ - az 485 . 66 4. 1 450

15 .'2S I 1. 0 I 7. I 25

:3S I J. 4 I I() • I. 4 0 I. 6 • I. ,') •. 7

'I. 0 • ). 0

1.4 7 L 2 •. 65 I. I

1J.:i •. 7

• I. 2 I , tl.'i g • 70 •. s • I. 6

:.l. 0 I.S

• I. 0 1.11 1.7

' I. 4 I. 7 I. i

IJ.!l I J. 7

I • 8:,!

I 8. 6

1 7 !I

I­

-I I '

-I .I

-I '!l. I

12

I 'I

1 1 i () --- :[

8. 4 I ........ , ..

1 u 1

. _

!1 ... ----I S. I

I 12 I 9. R :.'1

-I

1-I H.() I! ' I~- \l 1--1 5. 8 ...... I

:wo 4100 -135 260 3-15 170 :!lfl :Jsu 'l75 615 MO

-tll!i 4~1)

:lSO -110

8e• toot notes at end or tnbl<'.

114

Combustible

Limits of flurn- --, --rnu.bility (volumc-

percPnt) T, • A/1' --------- {0 Q) I (0 C)

sec-But\• I benzene ... _ tert-Butyl benzene_ .. . n-Butyl bromide. __ .. Butyl cellosolv!' .... _. n-Butyl chloride .... . n-Butyl formate ..... _ n-Butyl stearate .... .. Butyric acid ________ _ a-Butryoluctone. __ •. Carbon di9ulfide ..... _ -~ Carbon monoxide .. __ Chloroh.~nzmw ....... _ m-OrL~soL ...... __ .... . Crotonaldchyde. __ .. _ -1 (' U ffiPII e ... - _ .... - ... Cy11noe;cn. ____ ... _._-I Cyclohcptane. __ .... . Cyclohcxanc ...... __ _ CyclohcxanoL __ .. _. Cycloh!•xcne ........ _ Cyclohcxyl acetate .. Cyclopropan!•. __ ... Cymerw ... ---· __ .. __ Dt~cahoraue. _ .. _ ....... Decalin __ . __ . _ . ____ _ n-l>l'CIIlll' .. - ............ . I>•·utnium _. _. _ ... . J>i bomne .. __ .... _ ... _ Di!'S1·i ful'l ( liflce'.lll><') I>icth; I :~mit11• .. ____ . f)jl'lhfl ,. H lir·r• 1.1-llwthvl •· ··1.

l.lr.•lhyl !'Yl'lrrlr• 'il 1

')i•·thvl "t!H'r_ ;i, !Jfr•l h1·\ )lPII(!>lll

Dt~ 'hv 1 ht t<HIP

L,.

1 0. 77 I. 77

1 2. 5 8 l. l

1.8 1.7 • . 3

j 2. 1 8 2. ()

1.3 12. 5 1.4

8 l. l 2. 1 I. 8S 6. 6 I. 1 1.;{

• 1. 2 1).2 • 1. ()

'l. 4 1 • 8.'i .2

I • 7-1 12. 7.')

4. !I .s

l.S •. s I • S

. 7!l 1.!1

7 (i

I

u.. I -~-;,;-~~·~~~-i~o

I f). 8 .... _ .[ 4!)0 - ... - ~ - - -- -- ~ - 265

IO 11 24!) I JQ ----- --·

l'l. 2

II )(l

1 6. f)

6. 7 7. 8

10. ~ I fl. 5

I 4. !I 13 5. t:

75 s.~

10

21

!)7 i -l(i I

.. I I

!

:Hi5 450

HO

li-10

425

:,l;j()

:.!10

t· ~

I :w

Jm~ t'>~•L\1 c": l·i11oL. Dtiso 'ltlyl kt·l•··" --1

! -... "' to ti.

2-4, lJ ..;11P.\"1Jfl8t1' 11 __

Diisopr. ,,,,.r , 1 ftpr_

ililllt'lhyl •. II. I

2.~- Dirnrth1 ·llrllr.­:1,:!-l liloll'thy, ·I• :tile

'illlr·lhyJ dt•t1r j ,', d 1 t~'l /;;('ll!l·i '·"'

th 1 11'.

'lirroo·lhyl , ir"l' .•

1,, 'lim• tl1_vl : .. r.rlll-

I ·I

l !

llr . - . .. ., I 1., h 2,:i-l!. ·l,vl)ll'i !Hill'.' L I :2.2- 1>11 1.)·1 pro'''""' I ., I IJ,rrl"ti,, ;ulfidt• .... ! :.!. ~-llirw::,·vl -ulfoxid(• ___ : ...... . J)jo,.:. '. - ....... --I ~- \1 llipell'llt· ~.75,' !J·p!\Oii.}'llil'•ill' ___ _I I. 7 !

I li. :.l I

:,

'I)

!I I I

{' I

II

:!".: "b. I

I

1:.!0;

·lOll

·1 .-, •(

I,

.lPl'ENDIX A 115

----------~,--------------~----~ Limits of flam-mability (volume-

Combustible percent) TL AIT (o C) (o C)

Lu U,. ---------1-----1----------Di):henyl ether ___ .. __ Dipheuyl methane •. _ Dh illy I ether _______ _ n-Dodccane •• ______ _ Ethan~-------------Ethyl acetltte. ______ _ Ethyl alcot.oL •. ____ _ Ethyl amine ________ _ Ethyl iJenzene_-----­I~tltyl r;hloride. _. __ . -~ Ethyl cyclobLtt&nc. __ Ethyl ~yclohe.x&rH'- _ .. Ethyl cyclopcntane __ _ Ethyl fer mate ______ _ Ethyl lactate ..... __ _ Ethyl rnerCllptan ..... . Ethyl nitrate. ___ ._._ E.•.hyl nitrite._ .. __ . __ Ethyl propionate ..... Ethyl propyl ether_._ Ethyleu1• . ________ . _ Ethykneimine. _ ..... Ethylene glycoL •.... .~chylerw oxid,._ ••• _ Furfural alcuhul.. _ .• Gasuliue:

100/130 ... ····· 115/14!i_ __ ----·

filvrt><iuc _. _____ .. __ . n-ileptane .. _ .. __ _ 1<-IIPXII<ICCUll!' ••...••• n-lii'X!Ulr'- _ ....... . n-ll<'x\'1 alcohfll.. _ 11-llt>x)·l <'!her .. _. II ~·dmzilll'. _ .... _ 11,\'dl'Ugf'll. - . - -II ydrogpn \',\'1111 irh• __ . · liYdi'OI--(I'Il ,;ulfidf' ..... 1

l~;llllll\'IIH'"lnl<' _____ I l~o!llll~;J aleniJnl.. ' 'hmhul till<'.

l~oh•ll \'I al<'••hol .•. _' '"'' •Ill \·i h<•ft Zt'lll'

1

f><o)llll \·I fni'IIIH lt' b"hilt\·it•lf{' ]:-;op(•ttfar.•· . ! f-..•ljdilH'IIlH' -1

l"'i'""i'_-;Lll·r·t:llr• .1 1--•~J'!'CIJ'.\'l a:1•olud ),·,prnpvl hipiii'IIYI ,Jr-t fur·!.

.II

.II' fi I\ I •)'4\:-->illl'

'ft •t iJt~ I II \!,:II vi ... ·,·tal<' \f, .. :,,-1 tt<'•·! vlo·l .. -\1,-•1,\·1 :d'·"il<d \I<-<,,\'! "11\llif' -

\l<-111\'l !.rrHIIiri<­:1-\lt•l h\'1 bttlt'llt•-1 \It•! !• ,-)·hill yl kr•lflli<' .\It·! J,·\'1 .-.-iJ.',_,.,J\ ,. _ . \lr·il.~·l•·••llnHoh·•·:"'t'-

lUtt•_ :llo-thyl •·thy! f'lh;·r

l. 05 • . 43 1.2

11,:.! •. 6 4. 7 4. () 5. n 4. 0

I I. I 1).4

1.~ I J. 7

I .• '-':.! :.!. () 1.1-1 I. 4

. "' ' I 7 '.!. .. ! ... ti

ti. f' ;( ·~

J. ; h. I

• 4. 2 )(I

I. 5 ~ I :.!

·; :.!. ;,

.. 1. 7 • ~-:.!

~··I' ftl('fJwtPa nt t1nd of table.

75 4ti 4-1 I 7. () I !1. i1

:-:. ·l 1 II

111 f) ~)

1-1. !I \1. ti

....

I;", I I

IIi

I ! ; ~ (i

{;)

\I I .'-..II

,. :.!1.

i.----- 400

i: =:=: i~::: I 25 i ;lfj(l

-----1 J;i() ---"1 41'·11

-t:w

·IIi~>

jfill

1111

:.!Ill :.!:lO :.!Ill

-- IS'i [>-Ill

·! :! .... -, ~ i t;;rt

:!,11

·HI i I

I

Limits of flam- I mability (volume- ,.

peJcent.) I 'h AIT

Mothylohloddo ----- ~--Uu __ ('_]_~-C) Combustible

Methyl cyclohexane.- 1. 1

1

6. 7 _- ___ • 250 Methyl cyclopenta-

diene. __ .- ••. _ .. -- 1 1. 3 1 7. 6 49 445 Methyl ethyl ketone.. 1. 9 10 Methyl ethyl ketone

peroxide. - ... - . -.- --- - ..... .. Methyl format~------ 5. 0 23

40

Methyl cyclohexanol. ' 1. 0 ..... _____ • __ . MP.thyl isobutyl car-

390 465 295

binoL _ .. _ •. _ ..... •1.2 40 -----Methyl isopropenyl

ketone____________ 51.8 ~9. 0 __________ _

a-Methyl nai-hthale~oe •. 8 . _ ... _. _ . . .. . . . 530 Methyllactate _______

1

I 2. 2 ________ ------ ____ _

2, Methyl penta'le... •I. 2 --------.----- ____ _ Methyl propionatE>_._ 2. 4 13 • _ .•• __ .• _. Methyl propyl ketone., 1. 6 8 2 ___ •.. ___ .. Methyl atyrene __ .... I ' 1. 0 ,. _. _. _. _ 49 495 Methyl viny I ether .. ·/ 2. 6 39 _ .. _. -~- ___ _ Methylene chloride ... ------- ... ----- ______ 615 Monoisopropyl bicy- J

clohexy\__________ . 52 18 4. 1 124 230 2-l\lonoisofropyl ,

bipheny ---------- 10 .5:3 11 3.2 141 435 Monomcthylhydra-

zin c .. _ ... _ ... _ .. _ . 4 -------- ------ --·--~~ph~haJene _____ . _. N~eotme ............ . 1~: ~~~-- :o_ ~~ ~ _________ ~=~

3. 4 1-- -- .. --. Nit roet ha m• _ • __ •• __ _ Nitronwthaue. _ •• __ . 1-JIIitropropane. _. __ • 2-:'\itrop1·opane .•..•• n-.'\onarH~ .•••. __ •... n-Octnue .. __ •.. __ .. _ l'araldr.'hyde. _ ••• _. _ ·1 Pentahorane __ .. ____ .,

i. a _ . _____ _ 2. 2 ---.---2. 5 -- .. -.-

21 • R5 -. - - -- . -0. !15 1. 3

. 42 ------- -1.4 7. 8

30 33 34 27 31 13

---48 tl·l'entalle. --.--.--. -i Pentnrn..t!tvlenc ~~;lv- 1 Pl~;~~~~li,; ~~:·l;~:,j~i~~~:: . -~ i .- 2- -~- -22 ;,_ ~- --i-ii)-a-l'iroline •. .' ..... --- • 1. 4 1-l'iiiUill'. __ ..... _. __ .. n. 74 'a 7.:.! .... i Propndi<'m'. _.. 2. ltl

205 220

260

335 570 500

l'ropuu.-. _.. :2. I !I. 5 1

102 j ·150 1,:.!-l'roplllldiol ':.!.;:i '-- _1 __ 1 410 {j-J'ropiolnctoue a 2. \1 l'r••piOIIIIIrh•hyd\'. . 2. \1 1r-l'ropyl ttcdnt••- _. 1. ~ 11-l'rnpvlakohol. 12 :.?. :.! Prnp~·l'hlldllP :.,. fl

17

I ].j

l'rop~·l ddorid<•.. ' :.!. ·I 11-l'r"]',\'lllilrat\'_ _ 1' 1. .~ '1: Iiiii l'n '1•_1 lr·ll<· . :.!. ·I I I l'ru}:\ !•'"" ;!;,·ldoridt• ':1. I ~'n•I·~·krH· ~lyt'ol ::4 :.?. fi l'nqq·l~·r,•· u\jdf'. '.!. ·" 1'\'l'i•lll-•· II J_ '-. l'rup "cvl lth·,,J,.,I_ 1 ·• -1 (~ldll11ii·:~·. 4 1. 0 ~t vr•·r.~· 211 I. I ~tilf11r ~-· 2. 0 p-T·q,!,.·I•Vi . '·!IIi ,, .. 'J',·trnd~·<·a:rt·_ •. 5 rrt•t rah \'dn ,fur~lllt' '2 0 T<·tmlii,_ ... '· f--1 "D. o

I --- -!-

!

:.!I

1-

71

17!) 4GO

5:1.i :.!011

116 FLAMMABILITY CHARACTERISTICS Oli' COMBUSTIBLE GASES AND VAPORS

TABLE A-1. Surr.mury of limits of flamma­bility, [,,1ver tern peraturt limit.9 ( T L) and minimu11, autoignttion temperatures (AIT) of in4ividua.l ya.•u1s and t'a.pors 'lirt air at atmospltenc pressur13- Contiaued

-·--~------·-------

Limite of flam­mability (volume-

percent) TL AIT 1---,---1 (o C) (o C)

CombusMble

-----·----·· L,. 1--u-.. _·l---

2'~!~t~;:r~~·~~~~=~--~ 0.8 ~-------- ------ 430

~:~~~7~~-~~~~e;;~ ~~-== ·· -~- i." 2- -I-- -~-7." i- !~8 Trichloroethane .•.•.. ___ ... _ _I_....... 500 Trichlo:-:>ethylene .... 28 12 26 40 30 I 4:ZO Triethyl amine...... 1. 2 8. 0 _ ........ . Triethylene glycoL... s. 9 28 9. 2 •• _____ • _ .. 2,2,3-Trimethyl bu-

tane ... ------------Trlmeth_yl amine. __ ._ 2,2,4-Trtmethyl pen-

tane .••.•......... Trimethylene glycol .. Trloxane ............ . Turpentine .......••... Unsymmetrical di-

methylhydrazine ... Vinyl acetate •....... Vil!~l chloride ...... . m-Xylene. ____ • __ .. . o-"_ylene ... _. _. _ .. __ p-Xylene ....... _. ---

1. 0 2. 0

. 95 • 1. 7 • 3. 2

I, 7

2. 0 2. 6 3. 6

I 1. 1 I 1. 1 I 1. 1

1 lmlfl0° C, '1•47° c. '1•76° c. • Calculated. I t•ftO~ C. •1-8&0 c. 7 t-140 11 c. •1-1150" c. •1•110• c. 111•17&0 c.

"t-oo• c. nt-53° C. 11 t-86u C. II 1•130° C. "1•72°C. II 1•117° C. "1-125° c. 111•200° c. "1-78° c. 10 1•122° c.

12

95

420

415 400

33 ~·----- ----

; 3. 4 1 6. 4 I 6. 6

111-43° c. 111-195° c. tlo 1•160° c. "1•96° c. "1•70° c. •t-2£1• c. If ··247° c. 111•30° c. "1•203° c.

sao 465 530

APPENDIX B STOICHIOMETRIC COMPOSITION

The stoichiometric composition (G,) of a combustible vapor CnHmOAFt in air may be obtained from the equation

100 Thus, C,, ( k 2 ) volume-per-

1+4.773 n+ m-4·- ~

cent, where 4.773 is the reciprocal of 0.2095, the molar concentration of oxygen in dry air. The following table lists the values of C, for

a range of ( n+ m-!-2~) values from 0.5 to

30.75:

N1

o /_o_.2_5_1_o_.5o I

o______________ ________ ________ 29.53 1

l______________ 17. 32 14. 35 12.25 2______________ 9. 48 8. 52 7. 73 3 ______________ 6.53 6.05 5.65 4______________ 4. 97 4. 70 4. 45 5______________ 4. o2 a. 84 a. 67 6______________ a 37 a 24 a 12

7---- - - - - - - - - - - 2. 90 2. 81 2. 72 8 ______________ 1 2. 55 2. 48 2. 40 9______________ 2. 27 2. 21 2. 16 10.------------ 2. 05 2. 00 1. 96

0.75

21. 83 10. 69

7. 08 5. 29 4. 22 3. 51 3. 01 2. 63 2. 34 2. 10 l. 91

N• 0 0.25 0.50 0.75

---}l_ ____________ 1. 87 1. 8~ 1. 79 l. 75 12 _____________

1. 72 1. 68 1. 65 1. 62 13 _____________ 1. 59 1. 56 1. 53 1. 50 14 _____________ 1. 4'/ 1. 45 1. 42 1. 40 15 _____________ 1. 38 1. 36 1. 33 1. 31 16 _____________ 1. 29 1. 27 1. 25 1. 24 17 _____________ 1. 22 1. 20 1. 18 1. 17 18 _____________ 1. 15 1. 13 1. 12 1. 10 19 ______ " _______ 1. 09 1. 08 1.06 1. 05 20 _____________ I. 04 1. 02 1. 01 1. 00 21_ ____________ . 99 . 98 . 97 . 95 22 _____________ . 94 . 93 . 92 . 91 23 _____________ . 90 . 89 . 88 . 87 24 _____________ . 87 . 86 . 85 . 84

25.------------ . 83 . 82 . 81 . 81 26 _____________ . 80 . 79 .78 . 78 27 _____________ . 77 . 76 . 76 . 75 28.---. -------- . 74 . 74 . 73 . 72 29 _____ -------- . 72 . 71 . 71 . 70 30_------ ------ . 69 . 69 .68 . 68 -

m-k-2X t N=n+

4 -; where n, m, X, and k are the

number of carbon, hydrogen, O'<ygen, and halogen atoms, respectively. iu the combustible.

For example, the stoichiometric mixture com­position of acetyl chloride (C2H30Cl) in air may be found by noting that

m-k-2~ 3-1-2 N=n+-4--=2+ 4 2.0.

The entry for N=2.0 in the preceding table is 9.48 volume-percent, which is the value of C, for this combustible in air.

117

118

APPENDIX C HEAT CONTENTS OF GASES

(Keal/mole I)

T,"K co. H,O o, N,

298. 16 0 0 0 0 300 . 017 . 014 . 013 . 013 400 . 941 . 823 . 723 . 709 600 1.986 1. 653 1. 4541 1. 412 600 3. 085 2. 508 2. 2094 2. 125 700 4.244 3. 389 2. 9873 2. 852 800 5. 4~2 4. 29!:1 3. 7849 3. 595 900 6. 700 5.238 4. 5990 4.354

1,000 7. 983 6. 208 5. 4265 5. 129 1,100 9.293 7. 208 6. 265 5. 917 1,200 10. 630 8. 238 7. 114 6. 717 1,300 11. 987 9. 297 7. 970 7. 529 1,400 1a 360 10. 382 8. 834 8. 349 1,500 14.749 11. 494 9. 705 9. 178 1,600 16. 150 12.627 10. 582 10.014 1,700 17. 563 13. 785 11. 464 10. 857 1,800 18. 985 14. 962 12. 353 11. 705 1,900 2v.416 16. 157 13. 248 12. 559 2,000 21.855 17. 372 14. 148 13. 417 2,100 23.301 18. 600 15. 053 14. 278 2,200 24. 753 19. 843 15. 965 15. 144 2,300 26.210 21. 101 116. 881 16. 012 2. 400 27. 672 22. 371 17. 803 16. 884 2,500 I 29. 140 23. 652 18. 731 17. 758

I Oordoa, 1. li. TbermodynamiCII of Hlcb Temperature Ou Mil· tUM 11o11d Appllcatloa to Combuatloa Problemll. W ADO Tecbnlcal Report 67-33, 18DU&ry 11167, 172 pp.

APPENDIX D DEFINITIONS OF PRINCIPAL

SYMBOLS Symbol: D•/inillon

A_____ _ _ _ _ Constant. A'_ _ _ _ _ _ _ _ Al'ea. a_ _ _ _ _ _ _ _ _ Velocity of sound. B _________ Constant. C,, ________ Stoichiometric composition. Af/, _______ Heat of combustion. K _________ Hatio of duct area to vent area. k _ _ _ _ _ _ _ _ _ Thermal conductivity. L_ _ _ _ _ _ _ _ _ LowPr limit of flammability. L* __ . _ _ _ _ _ l\loditil'd lower limit value. LA,.. _ _ _ _ _ A \'!'fill(!~ carbon chain lPngth for

paraffin hydrocarbons ami correla­tion parametPr for aromatic hy­drocarbons.

L ,_ _ _ _ _ _ _ _ _ Lu\\ Pr limit of fiarnmahility at 1° C. Lf D _ _ _ _ _ _ _ Length to d ianwtPr ra t.io.

Symbol: M ________ _ M, _____ ·--NO; _______ _

n ________ _ p _________ _ P,.. _______ _ ::.P ___ .----P---------8•--------T_--------t_ ________ _ .,. _____ , ____ , u ________ _ u, _______ _ v ________ _ V'--------v _________ _

')'. --------

/1•/iiiUion Molecular weight. Mach number. Equilibrium mixture of NOa and

N 10, at a specified temperature u.nd pressure.

Number of moles. l'reSE<ure. Maximum pressure. Pressure rise. Partial pressure. Burning velocity. Absolute t<:Jmperature. Temperature. T:me delay before ignition. Upper limit of flammability. Upper limit of flammability at t° C. Volume. Critil)tll approach velocity. Liquid regression rate. Specific heat ratio.

119

SUBJECT INDEX A PaK~

Ac11ta ltlt>hyclo __ . _ .. _ _ _ _ _ _ __ .. _ .. _ ..... _ ........ --. 7:J At•t•tylt•uit• hydrot•ur·uoHIL __ .. _______ .. __ .... _.... .. • 53 Air-fuel r11 tio __ .. __ . ____________ ..... __ .. __ .. ___ • 21 Alcohols ...... _ ............ _________ --. - _ ..... _- ...... - t\5 Aldt•hytles ... __ .. - ______ .. ____ .... -- - _____ - _ .... - 73 Arnmouia _________ -----··------------ ·------ 77 n-Amyl alcohoL __ . ___________ .. _ .. _ .. ___ ..... _ .. _ ti7 Aromutic hydrocaroons _______ .. __ . __ . ___ -- .. _- 5\1 Autoignition •• _ •.. ________ .• _____ .. _ _ _ _ _ _ _ _ 4, 32, 41

B Barr: cades ... ____ ._ ... _________ ... - _____ .---- 17 BlaRt pressure ______ . __ .. ________ .. _ _ _ _ _ _ _ _ _ _ _ 16 Burgess-Wheeler Ia w. ________________ . _____ - 22 Burning velocity---··-··-------- ____ _ __ 42,45 Butadiene .••• _______ • ___ .. __ . _____ • ____ ---- 48, 53 n-Butane. ______ . _______________________ 21, 25, 32 Butene-1. _. ___________________ .. ___ • ____ 48, 50, 52 n-Butyl alcohoL __________________ .________ 67 lert-Butyl alcohoL. __ • _______ . _________ . _ .. _.. 68

c Carbon chain __ .. ____ .. _________ .. ____________ .. 41 Carbon monoxide .. __ _ _________ .. _ _ _ _ _ _ _ _ _ _ _ 97 Combustion equlltions ______________________ 21,117 Contact time .•.. _______ ------ ______ ··---_____ 4 Cool !tames •• ________ . _ _ _ _ ______________ .. _ 28 Copper acetyl! de.___________________________ 56 Crit•cal CIN-------------------· ----------- 11 Cyclopropane_. _____________ .. _____________ _ 64

D n-Decane. __ .. __ . ___ -. __ •• _. _-- .. -- _. ___ . ___ -Decane-dodecan€ blends. ___ . _- _________ . _ •. -Deco.nposition •.•. ________ .. ______________ .. _

g:~~!t~~~==============================~ Dlmethy I ether ______________ . _________ . ___ _ n-Dodccane _______________________________ _

E

21,25 32,43

51. 15

16,57 70

21,25

~~~t~~~~!~B--= == = = = = = = == = = = = = = = = ~ = =: = === = = = = = ~g Ethane. ______________ • __________ .. _. _ _ _ _ 21, 25, 28

Ethen------------------------------------- 69 Ethyl alcohoL ___________ • __ .. __ .. ________ ._ 67 2-Ethyl butanol. ___ •. __ .. ____ ...... __ .. _ .. ___ .. _ _ _ 67 Ethylene ___________________________________ 48,52

F Fl11me arreston _________________ .. _____ .. _. _ _ _ 18 Flame caps. ______ ...... __ .. ___________ . _ _ _ _ _ _ _ 2 Flame extinction __ .. ____ • ____ .. _. _____ .. _ .. _ _ _ _ _ 29 Flammability characteristics. ______ .. __ .. ______ 20 Foam ___ .. ___ .. _ .. __ ... ___ .. ____ .. __ .___________ R F'Jrmic acid_________________________________ 61 Freon-12. _____ • ___________ .. _ ...... __ .. _____ . _ _ _ 69 Fuel-air ratio _______________________ .. _ _ _ _ _ _ _ 21 Fuel blends._ .. ________ .. ____________________ 74

G Gas frfleing ... _______________ ... ___________ _ Gas mixtures. ________ ... _. _____ • _. ____ .... ___ _ Gasolh•e ... __ • _______ • _ •. _ •• _ .. ______ • _. -- .. _

120

13 3

13,82

H l'u~· IJ alo~cnated hydrocarbons. __ .. __ .. __ . -- ... _....... 102 11\'llt of fonnntion _________ ----·-·· .... -------. fll r~-llt•ptaue __ ---------------------------- 21. 25,35 lietl'ro~cnoous mixtures .... __ .. __ . _-. _____ .... _- 3 11-Hexntiecane ... -------------- ....... ------··. :ll, 2f> r1-llexane ............. --- .... ---------- ... __ ----- :.!l, 2[•, :l4 n-llexylall'ohoL ................ -··------·-- .......... li7 l[y(lraulic fluids--------------··----··-----·---- H5 llydro!!en .. __ .. __ .. _____ . __ .. _ .. ____ ... _ ............ ___ 77, H!l Hydrogen peroxide ..... __ .. _ ...... _ .............. _ .... _ .. __ .. til

I Ignition_ .. _ .. _ .. _ ................ _ .. _ ..... __ .. ____ .. _____ _ Ignition tt'rnperature ________ ·-·--- ---------lgnitibility limits. ___ .. _ .. __ .... _ .. _ .... _ ... __ .. ___ .. -lnl'rtlllg __ .... _ .. _ .. ___ .... _____ ...... ___ .... ____ .. ___ .. bobutylene .. _ ........ _ .. ___ . _ ........ _ ............ _ .... _ .. _ .. .

J JP-4 _____________________________________ _

K Kerosine .. _. __ ............... __ .. ________ .. ___ .. _ . ___ _ Ketones- ...... __ .... __ ........ __ .............. ___ .... __ .... __ ..

L Layering .... ____ . _________ .. _ .. _____ .. __ . _____ _ Le Chatelier's law ______________________ ...... Limits of flammability ......... ------------------Liquid mixtures __ . __ .... _ .... _ . _ ... _ .. - .. -.- .. - ....... Lower limit._ .... _ .. _ .. _ .... _ .. _ .. _._. ____ .. ____ .. _-Low pressure limits_ ... __ .. _ ... _____ .......... __ .. _ ..

M Methane _____ ...... ___ .. _______ .. _____________ _ Methyl acetylene ..... ------------------- ___ .. Methyl alcohoL .. __ .... _ .... _ .. __ .. __ .... __ ..... __ .. _ . Methyl bromide- .. _ .. _ ......... __ . - _ ............ -- ... -a .. Methyl butene-L ....• -------------------­MeLhyl formate •••.... ---------------------Methylene bistearamida. __ .... _ .. _ .. _ .. _ .. _ ..... ___ -\lethylene chloride. ____ - .. ---- __ - .... -- ..... _-Minimum oxygen value ________ -----··-----··-1\lis ts ____ .. __ .. ___________________________ .. _

!\fixer ... ··---------------------------------N

a -! 2

lS 48

11, !:l8

7 73

:l :H

2 31

2 12, 811

!l, 21 5:) 117

2~. Ill 48 71

7 102 ll

a. ll 4, 7

Natural gas.------------ -------------··---- '27, :w n-Nonane ...... ----------------------------- 21,25

0 n-Octane __ • _ .. _ .. _ ..... __ ...... __ . ___ .... _ ....... _ .... _ _ 21, 2:,

p P11raffin hydrocarbons_ .... _________ .. _ .. __ .......... _ 20, .i!\ n-Pentadecllne .. _ .. _ ... _ ........ ____ .. _ .. _______ .. _ .. _ _ 21 Pentane __ .. _ ...... _. _ ...... ________ .. _ .. __ .. _ .......... _ _ 24 n-Pentane ______________ ·--------------- 21, 25, :l:l Perft UO:'O metha:-J P _ _ _ ____ .. _ .. ____ .. ________ .... _ 2S Perfiuoropropane___________________________ 2S Peroxides .. __ .. _ .. __ ........ _ .... __ .. ___ ...... ______ 53, 70, I O:l Predetonation distance .. __ .. _ ...... __ .... __ .. _ .. _._.... 57 Pressure piling ..................... ------------ 58 Propadiene ... ---------·--·------------------ 4S

SUB,JEC'r INr>EX 121

Par• Propane .. __ .......... ______________ ... _. _ 21, 25, 31 lsopropylalcohol ------------------- ..... 115 n-PropylalcohuL ....... _____ . ___ . _............ 67 n-Propyl nitrate .................. _ ......... _. __ .... . . . 97 Propylt•ne ............................. _. ____ 48,51

0 (~uantity-distanr.e relationships.................... 05

R Raoult.'s law ........... _ ...................... .. Rectangular diagrar..... . . . . . . . . . . . .. . . . ..•.. ~cgrl'S!lion rate .......................................... . Relief diaphragms ....................... __ ......... .

s Shock wave .......................... ___________ _ Spark-energy .req~irement'! ........................... . Spontaneous 1gmt10n ................................... .. Spmy injection ............................. . Sprays_ ... _ ........ _ •• _ . _ . __ ......................... .

31 9

44 18

17 3 3

97 6

l•n.re Hulhu ,·ompounds..... ..... .... ..... ........... 74 Sulfur hclmfluorlde...... .. . . .. .. . .. . . . .. .. . . .. .. .. .. .. .. :.!1'!

T Temperature limit ...... _ ... _ .......... _ .......... _..... 11 n-Tctrndeca!le.- . .. .. . . .. .. . .... .. . . .. .. .. ... .. .... . .. . . .. .. . 21 Tetra lin ..... _ ... - ....... _..... .. .. .. .. .. .. . . .. . . . .. . . .. .. .. 7

~~~ ~=:.. -.. ~ = = ~ = = = ~ = = = = :: = = = ·: = =: = = =::: ~: ~ = = 1 ~ Triangular diagram. . .. .. .. . .. .. . . . . .. .. .. .. . .. .. .. .. . . .. . U Trichloroethylene......................... . . . . . . . . . . 102 n-Tridecane... .. .. . . . . .. . . .. . . . .. .. .. .. .. • . . .. .. . . . .. .. 21 Tube diameter ............. _ ............................. _ 3, 53, 57

u n- Undo;~cane .................... _ ..... _ ...................... _ _ 21 Unsuturated hydrocarbons........ .. . _ •... _ .. _ ... 47 Upper limit ............. __ .......... _ .... _ ••. __ ... _ 2, 23, 26

w Wall quAnchlng .......................... _____ --------- 3

X o-Xylene _______ .... _ .. ____ ---- .... - _ ......... . 60

R U.S. GOV£RNMLNT PRINTING Of'F'IC! 1885 <r---7~1·1121