Fire Prevention Rey-an Moreno

8/17/2019 Fire Prevention Rey-an Moreno

1/18


2/18

Presentation Structure

• What are electrical fires?

• Ignition factors for structure fires

• Electrical equipment involved

• Fire Triangle

• Main modes of ignition

• Arcing

• Excessive hmic heating

• External heating

• !o" do s"itch#oard faults lead to fires?

• Electrical fires ris$ mitigation measures


3/18

What are electrical fires?

Electrical fires do not exist

Fire

Protection

Association

Australia


4/18

Ignition factors for structure fires

%&eport on 'overnment Services ()*( +olume * Section ,-

The most prevalent ignition factors causing structure fires varies across .urisdictions/ 0ationall1 in ()*)2**3 for structure fires "here the cause of ignition

could #e determined3 the most significant factors reported "ere4

• unattended heat sources 5*6/7 89

• short-circuit, ground fault and other electrical failure (10.6 %)

• suspicious 5:/6 89


5/18

Electrical equipment involved

• Electrical "iring

• Electrical s"itch#oards

• ;ight fittings3 especiall1 halogen do"n lights

• Transformers

•


6/18

Fire Triangle


7/18

!o" do electrical "iring faults lead to ignitions?

• There are onl1 a fe" main modes in "hich electrical insulation3 or

com#usti#les close #1 to electric distri#ution components3 can #e

ignited

*9 Arcing

(9 Excessive hmic heating3 "ithout arcing

79 External heating

• Some ignition t1pes involve a com#ination of mechanisms3 so must

not #e vie"ed as mutuall12exclusive causes of fire


8/18

Mode *4 Arcing

• An arc can #e either a series arc or a parallel arc

• 0ote4 The occurrence of series arc decreases the current flo" in the

circuit3 thus an over2current protection device cannot #e expected to

respond

• =auses of arcing are4

a9 =ar#onisation of insulation

#9 Externall1 induced ionisation of air 5created #1 flames or an earlier arc9

c9 Short circuits


9/18

Mode *a4 Arcing 5car#onisation of insulation9

• Wiring in (>)>*6+ circuits largel1 insulated "ith P+=

• Esta#lishment of a car#onised path across an insulating material can #e via4

!igh voltage across the insulator surface =om#ined effects of moisture and pollutants on insulator surface 5"et

trac$ing9

• P+= exposed to ())27))@= charsBthe char is a semiconductor "hich can lead to lea$age currents

and arcing

• ;ea$age current flo" t1picall1 have pea$s no greater than 6)A 5actual pea$

value depends on resistance of particular circuit93 there could #e a long time

#efore a circuit #rea$er "ould #e expected to open


10/18

Mode *a4 Arcing 5=ar#oniCation of Insulation9 5(9

AS0DS 7***2()),4

The circuit2#rea$er "ill

not trip "hen continuousl1 carr1ing *))8

rated current trip "ithin ( hr "hen carr1ing *(68 rated

currenttrip "ithin min "hen carr1ing ())8 rated current trip "ithin 6 s "hen carr1ing ))8 rated

current for circuit2#rea$ers having current

ratings #elo" 6) A trip "ithin *) s "hen carr1ing ))8 rated

current for circuit2#rea$ers having current

ratings of 6) A and a#ove


11/18

Mode *#4 Arcing 5Externall1 induced ionisation of air9

• Intrinsic dielectric strength of air is a#out 7M+m 5except ver1 small gaps9

• Grea$do"n can occur at much lo"er values if air space is ionised #1

FlamesPre2existing arcs

• Hielectric strength in presence of flames )/**M+m

• If a serious arc2fault occurs in a distri#ution #us3 large amount of ionised

gases "ill #e e.ected "hich can travel a certain distance

• If ionised gases encounter another circuit3 the1 can cause a #rea$do"n and

ne" arcing at the second location

• Fire2induced arcing is the most common situation for arcing damage in fire

scenes


12/18

Mode *c4 Arcing 5short circuits9

• Short circuits can ta$e t"o forms4

A #olted short "here a good metal2to2metal contact is made across a full2thic$ness section of metal

An arcing short3 "here initial metal2to2metal contact is not sustained and

current flo"s through an arc

• Golted shorts t1picall1 trip the circuit #rea$er and unli$el1 start a fire

• Arcing shorts can cause melting of the material around the contact area "hich

ma1 start a fire


13/18

Mode (4 Excessive ohmic heating

• =auses of excessive ohmic heating4

'ross overloads 5rare cause of fire3 protection #1 overcurrent protectiondevices9

Excessive thermal insulation

Stra1 currents and ground faults 5documentation sho"s onl1 6A required

for ignition "hen a 72conductor3 P+=2insulated ca#le contacted agalvanised iron roof9

vervoltage 5lightning stri$e3 accidental deliver1 of high voltage into lo"

voltage "iring3 floating neutral9

Poor connections 5#ad "or$manship or mechanical means9


14/18

Mode 74 External heating

• Most cases of external heating involve the "ire or "iring device as JvictimK of fire

and not as initiator of fire

• Some situations do exist "here external heating of "iring serves as the

initiating eventB t1picall1 arcing occurred after sufficient overheating


15/18

!o" do s"itch#oard faults lead to fires?

• Electrical s"itch#oard thermal imaging

%The hot spot visi#le as a heat source sho"s aloose scre" connection to the circuit #rea$er/

We recommend that the ca#le to the

circuit #rea$er #e re2terminated/ If this is not

possi#le3 replace the fuse "ith a ne" circuit

#rea$er/-


16/18

!o" do s"itch#oard faults lead to fires 5(9?

• 0o fire seal around for ca#les entering electrical s"itch#oard

• AS0DS 7)))4()): clause (/,/: JFire2protective measuresK

Wiring associated "ith s"itch#oards shall #e installed in such a manner that3

in event of fire originating at the s"itch#oard3 the spread of fire "ill #e $ept

to a minimum/

There is a ver1 high ris$ that "iring that enter at the top or sides of a

s"itch#oard3 "ill contri#ute to the spread of fire/

An1 opening of 6mm diameter or greater requires sealing "ith a fire retardant

sealant/


17/18


• Fire prevention

Maintain full compliance "ith current AS0DS 7)))4()):

Expansion of the use of residual current devices 5&=Hs9 to all soc$et

outlet and lighting circuits rated up to () A

;imiting the num#er of circuits connected to an1 one &=H to three

&equiring the division of lighting circuits #et"een &=Hs "here the

num#er of #oth &=Hs and lighting circuits exceeds one

Arc fault protection must #e provided for all s"itch#oards "ith a

nominal suppl1 rated a#ove L)) A and should #e considered for all other

s"itch#oards

Ho not overload the po"er soc$ets or use po"er #oards 5if practica#le9


18/18


• Safeguard heat sources3 and com#usti#les

• Install appropriate fire protection measures

=orrect t1pe of porta#le fire extinguishers

Automatic fire suppression s1stem interloc$ed "ith automatic po"er

suppl1 cut2off

Fire Prevention Rey-an Moreno

Documents