petroleum storage tank fire

7/31/2019 Petroleum Storage Tank Fire

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Petroleum storage tank fire

Three basic methods of fire protection of Storage tanks are

SubSurface base injection Over the top application( Surface Application) Foam chamber Foam maker Foam Monitor Foam Tower Dike protection

Sub Surface Base injection

This method is is used on hydrocarbon fuel stored in cone roof Tanks

This method is unsuitable for protecting floating roof tank( open or covered),Cone roof tanks with

internal floater, or floating roof and dike protection

Produces foam using high back pressure foam maker located outside the storage tank. Expanded foam

is delivered through product line piping or through one dedicated for foam line.

- Discharge outlet must be one feet( minimum) above any water present at the base of the tank.-

High back pressure foam maker as pirate foam solution. It will give an expansion ratio of 2:1and 4:1.it can discharge against a back pressure as high as 40% of operating pressure (Back

pressure is the accumulation of head pressure of fuel inside the tank and the friction loss

between foam maker and the tank)

- Minimum operating pressure into HBFM -100psi- Foam velocity entering tank should not exceed 10 feet/sec for flammable liquid- Foam velocity for combustible liquid should not exceed 20 feet /sec

Discharge time and application rate for SubSurface application

Flashpoint 37.8C to 93.c 30 mins .10gpm/ftsq( 4.1 lpm/msq)

Fp


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Discharge Outlets

Type -2 discharge outlets Fixed Devices that delivers foam into burning fuel partiallysubmerges the foam and produce limited agitation on the surface .e.g Foam chambers and foam

makers

Type-3 discharge outlets Fixed or portable device that delivers foam in such manner that itfalls on the surface of the liquid causing agitation e.g hose stream nozzles, monitors

CONE ROOF TANK

Requires the use of foam chambers for surface application which prevents the flammable vapors to

enter the supply pipe line( Frangible rupture disc)

Floating roof foam makers dont contain vapor seal so it cannot be used in cone roof

Surface area when protecting single storage tank -3.14r2

Surface area of multiple tanks

Calculate the surface area of the most severe hazard which is the storage tank that will requirethe most foam concentrate protection.

when all the tanks contain the same fuel consider the largest tank to be most severe. When tanks contain different fuels determine the surface area discharge time ,application rate

for each tanks and then select the one which require the most foam concentrate

Minimum Discharge time and foam application rate for type-2 foam discharge device

Flashpoint 37.8C to 93.c 30 mins .10gpm/ftsq( 4.1 lpm/msq)

Fp


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Floating Roof Tank

Can be protected with floating roof foam maker or foam chambers. As flammable vapors are minimized

so vapor seal is not required. The piping from foam maker is above is above the floating roof of the tank

and open to atmosphere.

Top of seal protection requires a discharge time of 20 mins and an application rate of .30gpm/ftsq.

Below seal protection requires discharge time of 10 mins and application rate of 0.50gpm/ftsq

Supplementary hose lines and discharge times required for small spill fires or dike protection-

Fixed or portable hose lines with a minimum flow rate of 50gpm/nozzle

35 feet 1 10 min

35-65 feet 1 20mins

65 -95 feet 2 20 mins

95 to 120 feet 2 30 mins

>120 feet 3 30 mins

Dike protection

The dike area rather than individual storage tanks may be considered for hazard to be protected and a

fixed foam system using monitor, floating roof foam maker is required

Number of monitors minimum two

Floating roof foam makers 30 feet spacing discharge 60gpm flow or less

>60 gpm flow spacing 60 feet

Spill Fire protection

Hydrocarbon spill fires requires a minimum nominal foam application density of 0.1gpm/sq feet.

Therefore a 50gpm hand line has the capability to control and suppress 500sq ft of flame surface area.

Largest potential spill must be considered to determine the number type and location of the dischaegedevice as well as quantity of foam required.

Protection option Fixed system such as monitors oor portable equipment such as hand hose lines

Discharge time

15 mins for fixed systems


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15 mins with portable equipmentFoam monitors & hand line

Monitors are not to be considered as primary means of protection for fixed roof tanks over 60 feet dia

Foam hand lines are not to be considered as primary means for protecting tanks over 30 feet dia or hose

over 20 feet in height

Application Density & duration

Fp 37.8.c to 93.3.c 0.16 gpm/ft2( 6.5lpm/m2) 50 mins

< 37.8.c do 65mins

Crude do 65 mins

Polar Solvents Recommended by manufacturers 65mins

Flammable liquid having boiling points less than 100.f and products which has been burning for

sometime may develop heat layer which might require application rate as high as 0.2 to .25gpm/ftsq.

Full surface fire -0.25 gpm( 10.4 lpm /ft2) application rate may be required. Burning crude oil tank may

require application rate of 0.32gpm/ft2( 12.9 lpm/m2)

Elevated application rate provides a better chance of

Foam reaching the burning surface Fall out from delivery system Losses due to thermal updraft Breakdown of foam as it trvels through the flames to reach the burning fuel and the destruction

of the foam due to hot fuel and any hot metal surface.

Cooling water requirement

Cooling water requirement of involved tank shell is estimated by tank size/dia-

100 feet dia 750gpm ( 3metre cube/min)

120 feet dia 1000gpm( 4m3/min)

160 feet dia 1250 gpm( 5m3/min)

220feet dia 1500gpm ( 6m3/min)


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Cooling water required to protect each adjacent tank not shielded from the tank on fire is

500gpm(2m3/min)

Cooling water rate of0.05 gpm( 2m3/min) is sufficient to absorb 90% of the radiant heat.

Hoses

5inch dia hoses is preferred

One 5inch hose line for every 100gpm( 3.8m3/min) flow requirement.At this flow rate friction loss is 8.0

psi for every 100 feet

FOAM DAMS

Foam dam height should not be less than 12 inches

Foam dams are to be at least 1 feet but no more than 2feet from the edge of the floating roof

Number of fixed discharge points on an open top floating roof tank is determined by the circumference

of the tank

Spacing is based on height of the foam dams

40 feet of tank circumference when using 12 inch foam dam 80 feet of tank circumference when using 24 inch high foam dam

petroleum storage tank fire

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