Fixed Foam Protection System

In the early years of the oil industry, fire in astorage tank was a common occurrence. Virtuallyall products were stored in cone roof tanks built ofriveted steel plates and the roof was oftenconstructed with wood and tar coated paper.Tank fires were common especially after alightning storm. This costly experience graduallyled to improvements in better codes andguidelines for handling storage tank fires.Floating roof tanks were adopted for low flashpoint petroleum products and proved to be a mostreliable method of protection against losses due tofires. The less volatile products with higher flashpoints continue to be stored in welded steel coneroof tanks.

As the frequency of fully involved storage tankfires decreases to a more acceptable level, thesize of fire, when it happens, becomes larger dueto the increase in tank size and capacity. It isquite common to see tanks with diameters in ex-cess of 328 ft. (100 meters) capable of storing amillion barrels of product

One practical method to protect flammable liquidstorage tanks from fire is with a fixed or a semi-fixed foam fire protection system. Whenengineered, installed and maintained correctly,these systems will give many years of reliableservice. The foam system can be used for fireprevention, control or direct extinguishment of anyflammable or combustible liquid fire within thetank.

In order to select the correct foam system, it isnecessary to understand the following systems:

A Fixed System is a complete installation pipedfrom a central foam station, discharging throughfixed discharge devices on the hazard being pro-tected. Foam proportioning components are per-manently installed.

A Semi Fixed System is an installation where thehazard is equipped with fixed discharge device(s)which connect to piping that terminates a safe

FIXED OR SEMI-FIXEDFOAM FIRE PROTECTIONSYSTEMS FOR STORAGETANKS

distance from the hazard. (Normally outside thedike wall.) Foam producing materials are trans-ported to the scene after the fire starts and areconnected to the piping.

DEFINITIONS

There are three major types of tanks commonlyused for the storage of combustible or flammableliquids.

• Cone roof tank

• Open top floating roof tank

• Internal floating roof tank/Covered FloatingRoof

A Cone Roof Storage Tank has vertical sidesand is equipped with a fixed cone-shaped roofthat is welded to the sides of the tank. Tanks thathave been designed in accordance with APIstandards have a weak seam at the joint wherethe roof and sides meet. In the event of aninternal explosion, the roof separates and blowsoff leaving the tank shell intact. This systemallows the tank to retain its contents and anyresulting fire will involve the full surface of theexposed flammable liquid.

An Open Top Floating Roof Storage Tank issimilar to the cone roof tank in construction butwith the exception that it has no fixed roof. Apontoon type roof floats directly on the flammableliquid surface. This floating roof has a mechanicalshoe or tube seal attached to its full perimeter.The rim seal covers the space between thefloating roof and the tank shell ( side wall ).

An Internal Floating Roof/Covered FloatingRoof Storage Tank is a combination of both thecone roof and the open top floating roof tank.The tank has a cone roof but with the addition ofan internal floating roof or pan that floats directlyon the fuel surface. This type of tank can beidentified by the open vents in the tank side wallsjust beneath the roof joint. If the internal floatingroof is other than a steel double deck or pontoon

type, the fire protection system should bedesigned for full surface fires ( similar to cone rooftanks ). For the double deck or pontoon internalroofs of steel construction, a design for seal areaprotection shall be permitted (same as openfloating roof tanks).

Small quantities of flammable liquids aresometimes stored in horizontal style tanks whichnormally sit on saddles or in underground storagefacilities. This section applies only to the threemajor types of tanks as listed above.

IDENTIFY THE FLAMMABLE LIQUID

There are two basic classifications of flammableand combustible liquids:

• Hydrocarbon ( non water miscible ) and• Polar Solvent ( water miscible )

The Hydrocarbon family typically consists ofstandard petroleum products such as - Gasoline,Kerosene, Diesel, Jet Fuel, Heptane, Crude Oiletc. products that do not mix with water.

The Polar Solvent group typically consists of -Ethanol, Methanol, Ketone, Acetone etc. or pro-ducts that will mix readily with water.

All Chemguard U.L. Listed and Standard GradeFoam Concentrates are suitable for use onHydrocarbon fuel fires or spills.

Only Chemguard U.L. Listed and Standard GradeUltraGuard 3% and the 3%-6% ( at 6% propor-tioning rate ) Alcohol Resistant - Aqueous FilmForming Foam ( AR-AFFF ) concentrates aresuitable for use on Polar Solvent Fuel fires orspills.

NOTE: Pure MTBE is only slightly water miscible( approx. 4% - 6% ).

FLAMMABLE AND COMBUSTIBLE LIQUIDS

PER NFPA 11

Flammable liquids mean any liquid having a flashpoint below 100oF ( 37.8oC ) and having a vaporpressure not exceeding 40 psi (276 kpa)(absolute)at 100oF ( 37.8oC ).

Flammable Liquids are subdivided as follows:

Class I liquids include those having flash pointsbelow 100oF ( 37.8oC ) and may be subdivided asfollows:

(a) Class IA liquids include those having flashpoints below 73oF ( 22.8oC ) and having aboiling point below 100oF ( 37.8oC ).

(b) Class IB liquids include those having flashpoints below 73oF ( 22.8oC ) and having aboiling point above 100oF ( 37.8oC ).

(c) Class IC liquids include those having flashpoints at or above 73oF ( 22.8oC ) and below100oF ( 37.8oC ).

Combustible Liquids mean any liquid having aflash point at or above 100oF ( 37.8oC ). Theymay be sub-divided as follows:

(a) Class II liquids include those having flashpoints at or above 100oF ( 37.8oC ) andbelow 140oF ( 60oC ).

(b) Class IIIA liquids include those having flashpoints at or above 140oF ( 60oC ) and below200oF ( 93.3oC ).

(c) Class IIIB liquids include those having flashpoints at or above 200oF ( 93.3oC ).

FIRE PROTECTION OF STORAGE TANKS

U.L. has established two different types of foamdischarge outlets:

• Type II Discharge Outlet - A fixed device thatdelivers foam onto the burning liquid and partiallysubmerges the foam and produces restrictedagitation of the surface. Examples of this type ofdevice are Foam Chambers and Foam Makers.

• Type III Discharge Outlet - A fixed or portabledevice that delivers foam in a manner that causesthe foam to fall directly onto the surface of theburning liquid in such a manner that causesgeneral agitation. Examples of this type of deviceare Hose Stream Nozzles and Monitors.

There are two basic methods of fire protectionsystems for storage tanks:

• Sub-surface Base Injection

• Over the Top - (Subdivided as follows)Foam ChambersFoam MakersPortable Foam MonitorFoam Tower

SUB-SURFACE BASE INJECTION

The sub-surface method of fire protectionproduces foam with a "High Back Pressure FoamMaker" located outside the storage tank. Thissystem delivers the expanded foam mass throughpiping into the base of the tank. The pipe may bean existing product line or can be a dedicated fireprotection foam line. The expanded foam enteringthe tank through a discharge outlet is injected intothe flammable liquid. The discharge outlet mustbe a minimum of 1 ft. above any water that maybe present at the base of the tank. The foam willbe destroyed if injected into the water layer. Wheninjected into the fuel, the foam will rise through thefuel and form a vapor tight foam blanket on thefuel surface.

Advantages of Sub-surface

• The rising foam can cause the fuel in the tankto circulate which can assist in cooling the fuelat the surface.

• If there is an explosion and fire that coulddamage the top of the tank, the sub-surfaceinjection system is not likely to suffer damage.

• The discharging foam is more efficientlydirected to the fuel surface without anyinterruption from the thermal updraft of thefire.

Disadvantages of Sub-surface

• CANNOT be used in storage tanks containingpolar solvent type fuels or products thatrequire the use of AR-AFFF type foamconcentrates.

• Not Recommended for use in either FloatingRoof or Internal Floating Roof type tanks.

• Caution must be used so that the maximumfoam inlet velocity is not exceeded; otherwise,excessive fuel pickup by the foam as it entersthe tank will be experienced.

• Not to be used for protection of Class 1Ahydrocarbon liquids.

HIGH BACK PRESSURE FOAM MAKER

The HBPFM device is mounted in the foam lineused to aspirate the foam solution before it isdischarged into the storage tank base. It willtypically give an expansion ratio of between 2 -1

and 4 - 1. The device is capable of dischargingagainst considerable back pressure which can beas high as 40% of the operating pressure. Theback pressure is an accumulation of the headpressure of the fuel inside the storage tank andany friction loss between the foam maker and thetank. A minimum of 100 psi inlet pressure into theHBPFM is normally required to ensure correctoperation. The foam velocity through the piping tothe tank from the HBPFM is very critical. Withflammable liquids, the foam velocity entering thetank should NOT exceed 10 ft. per second andwith combustible liquids the foam velocity shouldNOT exceed 20 ft. per second.

The following chart shows the minimum dischargetimes and application rates for Sub-surfaceapplication:

Hydrocarbon Minimum MinimumType Fuel Discharge Application

Time Rate

Flash point between 100oF and 30 min. 0.10 gpm / ft.140oF (37.8oC and 93.3oC) 4.1 L/min./m

Flash point below 100oF 55 min. 0.10 gpm / ft.(37.8oC) liquids heated above 4.1 L/min./mtheir flash points.

Crude Petroleum 55 min. 0.10 gpm / ft.4.1 L/min./m

NOTE: The maximum application rate shall be0.20 gpm / ft. ( 8.1 L/min./m ).

FOAM CHAMBERSTYPE II DISCHARGE DEVICE

The Foam Chamber is normally used on coneroof storage tanks. The chamber is bolted orwelded on the outside of the tank shell near theroof joint. A deflector is mounted on the inside ofthe tank so that the discharging foam from thefoam chamber will be diverted back against theinside of the tank wall.

The foam chamber is mounted on the cone roofstorage tank wall shell in a vertical position justbelow the roof joint, or approximately 8" to 12"down from the roof joint to the center point of thefoam chamber outlet.

In sequence Chemguard Models FC 2.2, 3, 4 and6 foam chambers are to be mounted from approx.8" to approx. 12" down from the roof joint.

When the foam chamber is mounted correctly, theinternal glass seal of the chamber will be justslightly higher in elevation than the roof joint onthe storage tank.

Each foam chamber mounted on a cone roofstorage tank SHOULD have its own individuallyvalved riser supplying the foam solution fromoutside the dike area. For correct operation, aminimum of 40 psi is required at the inlet to thefoam chamber.

FOAM MAKERSTYPE II DISCHARGE DEVICE

The foam maker is normally used to aspirate foamsolution before being discharged inside a dike(bund) area or when used with external floatingroof tanks to supply foam to the rim seal area.

The discharge pipe down stream of the foammaker is sized to slow the velocity of theexpanded foam and shaped to deflect the foamback against the inside of the dike wall or onto asplash board or the tank shell wall when used forfloating roof seal protection.

The splash board is to be mounted above the topof the floating roof tank. The correct sizedischarge pipe from the foam maker should beinstalled per the information supplied in the dikeprotection system design information.

When mounted on a storage tank or used in adike protection system, the foam maker can bemounted in either a horizontal or vertical positionwithout any detrimental effect on foamperformance.

It is recommended that a minimum 12" length ofstraight pipe be installed upstream from the foammaker during the installation.

When using the Chemguard Model CGFM 1.5Foam Maker for a dike fire protection system, a3" diameter pipe with minimum length of 28" and amaximum of 100" must be connected to the foammaker outlet ( down stream side ). This length ofdischarge pipe allows for the correct foamexpansion to take place and slows the dischargevelocity. The Model CGFM 2.5 Foam Makerrequires a length of 4" pipe to be connected to thedischarge side of the maker. This length of pipeshould also be a minimum of 28" but can have a

maximum length of 120". The discharge pipe inboth instances should be directed back againstthe inside wall of the dike. This installation allowsa more gentle application to the flammable liquidwithin the dike and lessen the submergence of thefoam.

Criteria for sizing a foam system for a cone roofstorage tank.

• Identify the fuel inside the tank.

• Type of foam concentrate to be used.

• Calculate the fuel surface area (TTR2). *****

• Application rate.

• Type of discharge device required and quantity(based on fuel flash point and tank diameter).

• Calculate discharge duration.

• Supplementary hose lines required and dis-charge duration.

• Quantity of foam concentrate required.

• Establish bill of materials.

NOTE:

To determine the quantity of foam concentrate ina given quantity of foam solution, use the fol-lowing formula:

Multiply the foam solution by x .01 if using a 1% type of concentrate x .03 if using a 3% type of concentrate x .06 if using a 6% type of concentrate

EXAMPLE

Cone roof tank - 150 ft. diameter

Fuel - Gasoline

Foam Concentrate - 3% AFFF

Surface area - 75' x 75' x 3.1417 = 17,672 sq. ft.

App. Rate @ .10 gpm per sq. ft. ( Per NFPA 11).10 x 17,672 sq. ft. = 1,767.2 gpm of foamsolution required

Discharge device - Foam Chamber, Qty. 4required

Discharge Duration - 55 min. 1,767.2 x 55 =97,196 gallons of foam solution x .03 =2,915.88 gallons of 3% AFFF concentraterequired.

Supplementary Hose Lines required ( Per NFPA11) - Qty. 3 required ( each minimum 50 gpm ) (Tank dia. over 120 ft. )

Hose Line discharge duration ( Per NFPA 11) -30 min. ( Tank dia. over 95 ft. ) 3 x 50 = 150 x30 = 4,500 gallons of foam solution x .03 =135 gallons of 3% AFFF. 3,051 (135 + 2,916)gallons of foam concentrate required.

A suitable bill of materials of major componentsfor the above system using a bladder tank couldbe.

• 1 x 3,200 Gallon horizontal style bladder tank.

• 1 x 6" Between flange style ratio controller.

• 4 x Model FC6 foam chambers each with aflow rate of 395 to 1,050 gpm depending onincoming pressure.

• 1 x 2 1/2" Threaded type ratio controller (Forsupplementary system).

• 3 x 50 gpm handline nozzles.

• foam concentrate.

NOTE:

This chart identifies the number of Foam Cham-bers required for the protection of a flammableliquid contained in a vertical cone roof atmos-pheric storage tank where the discharge device isattached to the tank. Where two or more outletsare required, the outlets are to be equally spacedaround the tank periphery and each outlet is to besized to deliver foam at approximately the samerate.

Tank Diameter Meters Minimum Number (or equivalent of discharge area) outlets

Up to 80 ft. 24 1Over 80 to 120 24 to 36 2Over 120 to 140 36 to 42 3Over 140 to 160 42 to 48 4Over 160 to 180 48 to 54 5Over 180 to 200 54 to 60 6

It is suggested that for tanks above 200 ft. (60 m)in diameter at least one additional discharge outletbe added for each additional 5,000 sq. ft. ( 465sq. m. ) of liquid surface or fractional part.

This chart indicates the number of SUPPLE-MENTARY hose streams required for various sizetanks. Each hose stream must be capable of aminimum flow rate of 50 gpm of foam solution.

Diameter of Largest Minimum Number of Tank Hose Streams Required

Up to 65 ft. ( 19.5 m ) 165 to 120 ft. ( 19.5 to 36 m ) 2Over 120 ft. ( 36 m ) 3

This chart shows the Minimum discharge time andapplication rate for Type II fixed foam dischargedevices on Cone Roof storage tanks.

Hydrocarbon Application DischargeType Rate Time

Flash point between 0.10 gpm/ft. 30 min.100oF and 140oF (4.1 L/min./m)(37.8oC and 93.3oC)

Flash point below 100oF 0.10 gpm/ft. 55 min.(37.8oC) or liquids heated (4.1 L/min./m)above their flash points

Crude Petroleum 0.10 gpm/ft. 55 min.(4.1 L/min./m)

• Flammable liquids having a boiling point of lessthan 100oF might require higher rates ofapplication. These should be determined bytest.

• For high-viscosity liquids heated above 200oF,lower initial rates of application of foam may bedesirable to minimize frothing and thesubsequent expulsion of the stored liquid fromthe storage tank. Good judgment should beused in applying foams to tanks containing hotoils, burning asphalts or burning liquids thathave boiling points above the boiling point ofwater.

• The above table includes Gasohols andunleaded gasolines containing no more than10% oxygenated additives by volume. Wherethese additives exceed 10% by volume orwhere the flammable liquid is a polar solvent orwater miscible product, fire protection isnormally supplied by the AR-AFFF type foamconcentrates. In those instances check with

Chemguard to establish recommended appli-cation rates. The minimum discharge durationis 55 min.

The following chart indicates the minimumoperating time of the supplementary hosestream(s) for various size tanks.

Diameter of Largest Minimum Operating Tank Time

Up to 35 ft. ( 10.5 m ) 10 min.35 to 95 ft. ( 10.5 to 28.5 m ) 20 min.Over 95 ft. ( 28.5 m ) 30 min.

Equipment List using a Foam Pump Skid Assy.for a 150 ft. dia. tank containing gasoline.

1 x Atmospheric Foam Concentrate Storage Tank 3,100 Gallons

1 x Electric powered Foam Pump Proportioning skid with prepiped 6" ratio controller ( Foam Chambers ) and prepiped 2 1/2" ratio controller ( Supplementary Hose Lines )

4 x Model FC4 or FC6 Foam Chambers

3 x 50 gpm Hand Line nozzles

3,051 x Gallons 3% AFFF ( plus any additional for testing of the system )

NOTE:

When protecting multiple storage tanks the foamsystem is to be sized to protect the single largesthazard.

Fig. 9 depicts a manual foam pump skid systemshowing all necessary piping, valves, dischargedevices, ratio controller, foam pump and foamstorage tank for the above system.

Fig. 10 shows a Cone Roof Storage Tank with aSemi-Fixed Foam System.

The following example shows the foam systemrequirements for seal protection of a 150 ft.diameter open top floating roof tank.

Type of Tank - Open Top Floating Roof Tank

Diameter of Tank - 150 ft.

Type of Fuel - Gasoline

Foam Dam installed on roof - Yes - 2 ft. fromtank wall and 2 ft. in height

Sq. ft. area of annular ring - 930 sq. ft.

Application Rate - .30 gpm per sq. ft. ( PerNFPA 11).30 x 930 sq. ft. = 279 gpm of foam solution required.

Type of Discharge Device - Foam Makers

Discharge Duration - 20 min.279 x 20 = 5,580 gallons of foam solution - x.03 ( 3% AFFF ) = 167.4 gallons of foamconcentrated

Quantity of Foam Makers Required ( Per NFPA11) 6 required.

Add supplementary hose lines per example forCone Roof Tank with Foam Chambers.

NOTE:

The number of fixed foam discharge points on anopen top floating roof tank is determined by thecircumference of the tank.

The maximum spacing between discharge pointsis 40 ft. ( 12.2 m ) of tank circumference whenusing a 12" ( 305 mm ) high foam dam and every80 ft. ( 24.4 m ) of tank circumference when usinga 24" ( 610 mm ) high foam dam.

In accordance with NFPA 11

Foam Dam Design - The foam dam should becircular and constructed of at least No. 10 USStandard Gage Thickness ( .134 in./3.4 mm )steel plate. The dam is to be welded or otherwisesecurely fastened to the floating roof. The foamdam is designed to retain foam at the seal area ata sufficient depth to cover the seal area whilecausing the foam to flow laterally to the point ofseal rupture.

Dam height is to be at least 12" ( 305 mm ) andshould extend at least 2" ( 51 mm ) above anymetal secondary seal or a combustible secondaryseal using a plastic foam log.

It is to be at least 2" ( 51 mm ) higher than anyburnout panels in metal secondary seals.

Foam dams are to be at least 1 ft. ( 0.3 m ) butno more than 2 ft. ( 0.6 m ) from the edge of thefloating roof.

Foam solution & rain water is to be drained by,slotting the bottom of the dam on the basis of 0.04sq. in. of slot area per sq. ft. (278 mm sq./sq. m)of diked area while restricting the slots to 3/8 in.(9.5 mm) in height. Excessive dam openings fordrainage should be avoided to prevent loss offoam through the drainage slots.

SUB-SURFACE SYSTEM

( Sub-surface injection of foam is generally notrecommended for fuels that have a viscositygreater than 2,000 ssu ( 440 centistokes ) at theirminimum anticipated storage temperature ).

Example of a Sub-Surface Base Injection System

Cone Roof Tank - 80 ft. diameter

Fuel - Gasoline

Foam Concentrate - 3%-6% AR-AFFF

Surface Area - =40' x 40' x 3.1417 = 5,026.7 sq. ft.

App. Rate - .10 gpm per sq. ft..10 x 5,027 sq. ft. = 502.7 gpm of foam solution

Discharge Duration - 55 min.

Quantity of Foam Concentrate required -503 (502.7 ) x 55 x .03 = 829.95 gallons

Discharge Device - Qty. 1 High Back PressureFoam Maker ( " Foam generator " )

Number of Discharge outlets inside tankQty. 1 (Tank 80 ft. or less) (Per NFPA 11)

Supplementary hose lines per example for ConeRoof Tank.

The following chart shows the number of dis-charge outlets required inside the tank.

Tank Diameter Number of Discharge Outlets RequiredFlash Point below Flash Point 100oF100oF (38oC) (38oC) or Higher

Up to 80 ft. ( 24 m ) 1 1Over 80 to 120 ft. ( 24 - 36 m ) 2 1Over 120 to 140 ft. ( 36 - 42 m ) 3 2Over 140 to 160 ft. ( 42 - 48 m ) 4 2Over 160 to 180 ft. ( 48 - 54 m ) 5 2Over 180 to 200 ft. ( 54 - 60 m ) 6 3Over 200 ft. ( 60 m ) 6 3

Plus 1 outlet for Plus 1 outlet foreach additional each additional5,000 sq. ft. 7,500 sq. ft.(465 sq. m) (697 sq. m)

Equipment list for the above example using abladder tank foam supplied foam system.

• 1 x 900 Gallon vertical style bladder tank.

• 1 x 4" Between flange style ratio controller.

• 1 x 2 1/2" Threaded type ratio controller ( forsupplementary hose lines ).

• 1 x Model CFM500 High Back Pressure FoamMaker ( HBPFM ).

• Supplementary hand line nozzles and foamconcentrate.

Determining Number of Discharge Outlets forSubsurface Base Injection.

The number of discharge outlets required is bas-ed on the tank diameter and the flash point of thefuel as shown in the above chart.

FOAM MONITORS AND HANDLINES

Monitors are not to be considered as the primarymeans of protection for fixed roof tanks over 60 ft.in diameter. Foam handlines are not to beconsidered as the primary means of protection fortanks over 30 ft. in diameter or those over 20 ft. inheight.

Application Rates Using Monitors orHandlines

The minimum foam solution application rate isbased on the assumption that all discharging foamwill reach the area being protected. In consider-ing actual solution flow requirements, considera-tion should be given to potential foam losses fromclimatic conditions and thermal updraft of the fire,etc.

The following chart shows application density andduration for monitors and handlines on tankscontaining hydrocarbons.

Hydrocarbon Type Minimum MinimumApplication Rate Discharge

gpm/ft2 (L/min.)/m2 Time(min.)

Flash point between100oF and 140oF(37.8oC and 93.3oC) 0.16 6.5 50Flash point below 100oF(37.8oC) or liquids heatedabove their flash points 0.16 6.5 65Crude Petroleum 0.16 6.5 65

Included in the above table are gasohols andunleaded gasolines containing no more than 10percent of an oxygenated additive by volume.

On tanks containing water miscible/polar solventflammable liquids the recommended foam appli-cation duration is 65 minutes.

Flammable liquids having a boiling point less than100oF and products that have been burning forsome time can develop a heat layer which mightrequire foam solution application rates as high as.2 or .25 gpm per sq. ft.

Where monitors or handlines are used to protectstorage tanks containing polar solvent or watermiscible liquids the discharge duration shall be aminimum of 65 minutes at the recommendedapplication rate.

FSFPrv 995

TECHNIQUE IN EXTINGUISHING LARGETANK FIRES

Large storage tank fires are very complex eventsand satisfactory extinguishment requiresmethodical planning and the effective use ofresources. At this time, existing Codes andStandards do not provide guidelines for using highflow monitor foam applications for large tank fires.The existing Codes and Standards do providegood recommendations for fixed fire protectionsystems. Full surface fires involving largediameter tanks have occurred around the world.Extinguishment of such fires has not been totallysuccessful. With the introduction of large capacityfoam monitors, new varieties of foamconcentrates and improvements in applicationtechniques there has been some degree ofsuccess in achieving extinguishment.

The largest fully involved tank fire that has beensuccessfully extinguished was 150 ft. (46 meter).The extinguishment was carried out with a largecapacity monitor/cannon applying non-aspiratedfoam "over-the-top" onto the burning surface. It isbelieved that present fire fighting technology iscapable of extinguishing fully involved tank firesup to 197 ft. (60 meters) in diameter. In theory itmay be technically feasible to extinguish tank firesin excess of 200 ft. (61 meters) using the "over-the-top" method of employing very large capacitymobile monitors with improved types of foamconcentrates. The logistics for mounting suchmassive operations must be fully considered.

APPLICATION RATE

NFPA 11 application rate for mobile equipment isoften interpreted as 0.16 gpm/ft2. (6.5 L/min./m7).

The code also states that flammable liquidshaving a boiling point of less than 100oF (37.8oC)may require higher rates of application. In addi-tion flammable liquids with a wide range of boiling

STORAGE TANKPROTECTION WITH HIGHFLOW MONITORS

points such as Crude Oil may require applicationrates of 0.2 gpm/ft2. (8.1 L/min./m2) or more. Theapplication rate stated in the code is based on theassumption that all the foam solution reaches theburning surface.

Note: The rates are intended for Liquid Hydro-carbon Fuels. Polar solvent liquids are destruc-tive to regular foams and require the use ofalcohol resistance foams. Chemguard, Inc.should be consulted to determine the recom-mended application rate.

In view of the above, rates and practicalexperience gained in incidents involving fullsurface fires involving large storage tanks, itwould be more appropriate to consider 0.25gpm/ft2. (10.4 L/min./m2) which is equal to a 60%increase for mobile systems. For burning crudeoil tank a rate of 0.32 gpm/ft2. (12.9 L/min./m2)may be more appropriate.

The elevated application rates provide a betterchance of ensuring foam reaching the burningsurface thus increasing the probability for extin-guishment. Consideration for such high ratestake into account fall out from the delivery system,losses due to strong thermal updraft, break downof foam as it travels through the flames to reachthe burning fuel and destruction of the foam dueto the hot fuel and any hot metal surface.

WATER AND FOAM CONCENTRATE RE-QUIRED FOR FIGHTING LARGE TANK FIRES

Water supply both in terms of pressure, flow rateand adequate amount of foam concentrate areamong the most important factors for launching asuccessful extinguishing operation. Unless ade-quate and uninterrupted supply is guaranteed, anattempt to extinguish a fully involved large tankfire is doomed to failure at the very onset of theoperation.

The amount of water and the flow rate needed toproduce 3% foam solution to generate foam tofight a large tank fire can be found in Table 1.

The quantity of 3% foam concentrate and the flowrate needed to produce 3% foam solution togenerate foam to fight a large tank fire can befound in Table 2.

COOLING INVOLVED TANK AND THE PRO-TECTION OF ADJACENT TANKS FROM RADI-ATED HEAT SOURCE

With reference to existing guidelines, the amountof water needed to cool the involved tank shell isestimated by tank size:

100 ft. (30 meter) diameter 750 gpm (3m3/min.)120 ft. (36 meter) diameter 1000 gpm (4m3/min.)160 ft. (48 meter) diameter 1250 gpm (5m3/min.)220 ft. (67 meter) diameter 1500 gpm (6m3/min.)

Cooling water required to protect each adjacenttank not shielded from the tank on fire is 500 gpm(2 m3/min.).

In practice water applied to the shell of a largetank on fire is ineffective in preventing it frombuckling and deforming. In the late stages ofextinguishment, cooling water applied on the areaabove the liquid level would help the foam stay incontact with the tank shell. The cooling streamsshould be stopped when foam attack has startedto conserve water and to concentrate on extin-guishment.

The need for protecting adjacent tanks can bestbe illustrated with information and data publishedin a recent study done on large tank fires.Although not yet fully validated it neverthelessprovides valuable information for pre-fireplanningpurposes.

The time required to create an escalation condi-tion in an adjacent tank depends upon a numberof factors including: tank size, separation, type,initial boiling point of flammable liquid in the tanks,water cooling, tank design, wind speed anddirection.

For example, a full surface fire involving a 164 ft.(50m) diameter open top, floating roof naphtha

tank fire could be expected to fully involve aneighboring identical tank in approximately 1.5hours under the following conditions.

- 4 m/sec.(14 km/hr.) wind towards neighboring tank- intertank separation of 0.5 diameter (82 ft.) (25 m)- neighboring tank having pontoon roof and inadequate water spray protection

Altering any of the above conditions can changethe time for ignition of the adjacent tank:

Base Case = 1.5 hrs.

Change of conditions:

Calm (no wind condition) = 2.8 hrs.Intertank separation increased to 1.0 D (50 m)

= 3.0 hrs.Intertank separation increased to 2.0 D (100 m)

= 17.0 hrs.Water protection on side facing exposure

= 2.8 hrs.Double deck roof on exposed tank

= 1.5 hrs.Water protection on side facing exposure +double deck roof = 24.0+hrs.Tank diameters only 30 m but with 0.5 Dseparation = 0.5 hrsNeighboring tank contains kerosene, not naphtha

= 22.0 hrs.

Some conclusions drawn from the results are:

− − escalation is likely for unprotected tanks ofvolatile material with normal separation unlessthe original fire is extinguished quickly

− calm conditions only delay the escalationpotential

− increased separation alone only delays theescalation potential

− water spray protection or roof insulation alonedoes prevent escalation

− water spray and roof insulation together areeffective

− smaller diameter tanks at normal separationare at greater risk of escalation than largerdiameter tank

− − lower volatility fuels provide more responsetime for fire fighter

Cooling of adjacent tanks is best achieved withfixed systems that are designed to provide effec-tive water film coverage of all exposed metalsurfaces. A cooling water rate of 0.05 gpm/ft2.(2.0 L/min./m2) is sufficient to absorb 90% ofincoming radiant heat. Any increase in thecooling water rate does not increase the coolingeffect significantly. The figure of 10.2 L/min./m2

by NFPA 15 relates mainly to the protection ofpressurized vessels such as LPG tanks subject todirect flame impingement.

OVER THE-TOP-APPLICATION TECHNIQUEWITH LARGE CAPACITY FOAM MONITORS

A present concept in extinguishing large tank firesis to employ Large Capacity Non-aspirated FoamMonitors to apply foam "over-the-top" of theinvolved tank onto the burning fuel surface.Although they are normally known as non-aspirated monitors, these monitors are capable ofproducing foam with an expansion ratio of about3.1 to 4.5 when used with alcohol resistance typefoam concentrates.

Chemguard has large capacity foam monitorscurrently available have capacities ranging from2,000 to 4,000 gpm (7,570 L/min.). The equip-ment operates at inlet pressure between 100 to130 psig (690 to 890 kPa) and have a range ofabout 250 to 300 feet (61-99 meter).

AR-AFFF type foam concentrate is preferred andit should be transported in bulk totes or trailershaving large capacities. The logistics for trans-porting foam in 5 gallon pails or 55 gallon drumsto the fire scene should not be considered, forobvious reasons.

Large diameter hose should be used to supply theflow required for large volume foam attack. Theuse of 5" (125 mm) diameter hose is preferreddue to low frictional loss and is relatively easy touse. It must be remembered that it is extremelydifficult to move the hose once it is charged withwater. For quick estimation, provide one 5" (125mm.) hose line for every 1,000 gpm (3.8 m3/min.)flow requirement. At this flow rate the friction lossis 8.0 psig (55 kPa) for every 100 feet (30.5 m).Table 3 provides information on friction loss ofsome large diameter hoses.

The “over-the-top” foam technique attacks theburning tank with either a very large capacitymonitor that meets the required application rate or

combines several monitors to form a MassStream discharging with the wind to concentrateon a selected landing zone within the tank.

This extremely high “local application rate/density”promotes survivability of the foam journey throughthe fire to establish a foothold on a relatively smallarea of the burning surface. Once the foamblanket at the landing zone is established it canthen be expanded by making adjustments to theMass Stream. The added advantage of largevolume application in a small area may help toreduce “local fuel temperature” and the associatedactual vapor presssure which in turn can help inlowering the fire severity. These factors requireconsideration because as the fuel temperatureapproaches the boiling point of water, it is difficultfor the foam to survive. As fuel temperatureincreases the true vapor temperature will increaseto overcome the effectiveness of the foamblanket.

Large volume foam attack should be launched asquickly as possible; however, it must be stressedthat application must not be carried out until allequipment and logistic support are in place. Thelonger a tank is allowed to burn, the danger ofescalation becomes greater, the fuel temperatureincreases making it more difficult to extinguish,the exposed tank shell deforms (normally theexposed steel curls inwards to create nooks andcrevices) making it difficult for foam to cover allthe burning surface. In the case of crude oil, thepossiblility of having a “boilover” increases withtime.

The ability to deal with large tank fires depends onmethodical pre-fire plan, regular training andexervises. The most important factor, however,rests on minimizing the risk of having a fullyinvolved large tank fire through good engineeringdesign, effective management and maintenanceprograms.

STPrv995

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EXAMPLE OF BALANCE PRESSURE PUMPSKID WITH TWO PROPORTIONERS

WaterInlet

FoamConcentrate

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Flush InletConnectionFlush Outlet

Connection

Atmospheric Tank

Pressure ReliefValve

BalancingValve

RatioController

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System 1: Foam solutionto manifold supplying 4 foamchambers on cone roof tank.

System 2: Foam solution toseparate storage tank systemor hose reels, if required.

Pressure Vacuum Vent

FIG. 9

D004rv895

FUEL

AeratedFoam

FoamChamber

Dike Wall

Foam ChamberTopside Applicationon Cone Roof Tank

SEMI-FIXED FOAM SYSTEM WITH MOBILEAPPARATUS SUPPLYING THE FOAM SOLUTION

FIG. 10

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4 Outlets

TYPICAL OUTLETS FOR SUB-SURFACE INJECTIONINSIDE CONE ROOF STORAGE TANKS

Gate ValveCheck Valve

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EXPANDED FOAM VELOCITY vs PIPE SIZE2 1/2", 3", 4", 6", 8", 10", 12", 14"

Standard Schedule 40 Pipe

All dimensions in inches (millimeters)unless otherwise noted

EXPANDED FOAM RATE

FOAM VELOCITY vs PIPE SIZE - 16", 18"Standard Schedule 40 Pipe

16"

(400)18"

(460)

All dimensions in inches (millimeters)unless otherwise noted.

M/S

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3 10

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EXPANDED FOAM RATE D038rv195

0 200 400 600 800 1000 1200 1400 1600 1800

FOAM FLOW - gpm

FOAM FLOW - gpm

60

50

40

30

20

10

50

40

30

20

10

FOR SI UNITS1 gpm = 3.785 / min.

1 psi = 6.895 kPa1 ft. = 0.305 m

l


1 psi = 6.895 kPa1 ft. = 0.305 m

3" PIPE DIAMETER

2 1/2" PIPE DIAMETER

0 400 800 1200 1600 2000 2400 2800 3200

4" PIPE DIAMETER

These subsurface graphs depict the friction loss characteristics of foam with an expansion of 4 to 1 and inletvelocities for various pipe sizes. The 4 to 1 ratio is the value to be used for friction loss and inlet velocitycalculations.

D075rv195

FRICTION LOSS OF EXPANDED FOAMTHROUGH VARIOUS SIZE PIPES

FOAM FLOW - gpm

FOAM FLOW - gpm

50

40

30

20

10

0


1 psi = 6.895 kPa1 ft. = 0.305 m

l

1600 2400 3200 4000 4800 5600 6400 7200 8000 8800

6" PIPE DIAMETER


1 psi = 6.895 kPa1 ft. = 0.305 m

l

0 4000 8000 12000 16000 20000 24000 28000 32000

14" PIPE DIAMETER

25

20

15

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Foam Maker

Foam Solution

Weather Shield

AspiratedFoam

Seal

Typical Below Seal ApplicationTypical Top of Seal Application

PontoonRoof

Foam Dam

Aerated Foam

FoamSolution

FoamMaker

EXAMPLES OF TYPICAL TOP AND BELOW SEALAPPLICATIONS FOR FLOATING ROOF TANKS

Brace

D005rv195

Quick Opening Valve

Siamese Foam Hydran

StairwayPlatform

Stairway

Wind Girder

Solution Piping

Tank Shell

SEAL AREA PROTECTION USING A FOAM MAKEROR HANDLINE NOZZLE FROM LADDER AREA

Foam Dam

Back Board MountedHigher than Uppermost

Position of Roof

Ladder

Brace

Floating Roof

Product

Foam

D022rv195

Foam Maker

Siamese Foam Outlet forHandline Connection

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3rv1

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6rv1

95

SwingCheckValve

GateValve

Tank Shell

FoamFlow

Valved Test Connection

Rupture Disc(optional)

From High BackPressure Foam Maker

At Least 1 ft.(0.3m)

Water Bottom

D012rv195

TYPICAL ARRANGEMENT FOR SUB-SURFACE SYSTEMSINTO A CONE ROOF STORAGE TANK

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7rv1

95

Mechanical Shoe Seal.1 - For each 130 ft. (39.6 m) of tank circumference

(no foam dam required)Tube Seal - Over 6 in. (15.2 cm) from top of seal to top ofpontoon with foam outlets under metal weather shield orsecondary seal.1 - For each 60 ft. (18.3 m) of tank circumference

(no foam dam required)Tube Seal - Less than 6 in. (15.2 cm) from top of seal totop of pontoon with foam outlets under metal weathershield or secondary seal.1 - For each 60 ft. (18.3 m) of tank circumference

[foam dam at least 12 in. (30.5 cm) high required].

0.30 gpm. (1.14 L/min.) per sq. ft. (sq. m) of annular ringarea with foam dam or with foam application under metalweather seal or secondary seal. 0.50 gpm (1.9 L/min.) persq. ft.. (sq. m for all other applications).

20 min. - with foam dam or under metal weather shield orsecondary seal.

Not covered by NFPA 11.

Monitors not recommended.

Handlines are suitable for extinguishment of rim firesin open-top floating roof tanks.

0.16 gpm/ft.(6.5 L/min./m )For rim fires in open-top floating roof tanks.

2

2

Use same times as for open-top floating roof tank rimfires.

Not Recommended.

Not Recommended.

Not Recommended.

Not Recommended.

Not applicable.

Not Applicable.

Not Applicable.

Not Applicable.

Monitors for tanks up to 60 ft. (18.3 m) indiameter.Hand hoselines for tanks less than 30 ft.(9.2 m) in diameter and less than 20 ft.(6.1 m) high.

0.16 gpm/ft.[(6.5 L/min.)/(m )]

2

2

Flash point below 100 F (37.8Flash point 100 F - 140 F

C)

Crude Oil

o o

o o

Same as table for foam chambers.

Minimum 0.1 gpm/ft. [(4.1 L/min.)/m. ] ofliquid surface.Maximum 0.2 gpm/ft. [(8.2 L/min.)/m. ]Foam velocity from outlet shall not exceed10 ft. per sec. (3.05 m per sec.) for Class 1Bliquids or 20 ft. per sec. (6.1 m per sec.) forall other liquids.

2 2

2 2

Flash point 100 F (37.8 C)to 140 F (194.4 C)Flash point below 100 F (37.8 C)Crude Petroleum

o o

o o

o o

Not Recommended.

For S1 units: 1 gpm/ft. = 40.746 (L/min.)/m ; 1 ft. = 0.305 m; 1 ft. = 0.0929 m ; 1 in. = 0.0245 m; C = F - 32/1.8.2 2 2 2 o o

NumberRequired

HydrocarbonApplicationRates

DischargeTimes

PolarSolvents

Size ofTank


DischargeTimes

NumberRequired


DischargeTimes

PolarSolvents

Fixed-Roof (Cone) Tanks Pontoon or Double-Deck Floating Roof Tanks

STORAGE TANK PROTECTION SUMMARY

65 min.50 min.65min.

30 min.

55 min.55 min.

D056rv0200

Numberof FoamOutletsRequired


PolarSolventRates

Fixed-Roof (Cone) Tanks andPan-Type Floating Roof Tanks

Pontoon or Double-Deck FloatingRoof Tanks, (Open-Top or

Covered) Annular Seal Area

STORAGE TANK PROTECTION SUMMARY

Up to 80 ft. (2.44 m) dia.81 to 120 ft. (24.7 - 36.6 m) dia.121 to 140 ft. (36.9 - 42.7 m) dia.141 to 160 ft. (43 - 48.8 m) dia.161 to 180 ft. (49 - 54.9 m) dia.181 to 200 ft. (55.2 - 61 m) dia.Over 210 ft. (61.2 m)

1 Foam Chamber2 Foam Chambers3 Foam Chambers4 Foam Chambers5 Foam Chambers6 Foam Chambers1 additional for each

5,000 sq. ft.

1 for each 40 ft. (12.2 m) of circumferencewith a 12-inch (30.5 cm) high foam dam.

1 for each 80 ft. (24.4 m) of circumferencewith a 24-inch (61 cm) high foam dam.

0.10 gpm (0.38 L/min.) per sq. ft. (sq. m) of liquid surface. 0.30 gpm (1.14 L/min.) per sq. ft. (sq. m)of annular ring area between tank walland foam dam.

Not covered by NFPA 11.See Manufacturer's Approval Report.

Flash Pt. 100 F - 140 F (37.8 C - 194.4 C)Flash Pt. below 100 F (37.8 C)Crude Petroleum

o o o o

o o

Type I

20 min.30 min.30 min.

Type II

30 min.55 min.55 min.

20 min.

Type IType II

30 min.55 min.

Not covered by NFPA 11.

HydrocarbonDischargeTimes

PolarSolvents

D057rv195

Fixed Foam Protection System

Documents

fixed roof

cone roof storage tank

cone roof tank open

flash o o points

roof joint

roof separates

open floating roof tanks

o o boiling point