Fire Hazard Calculations for Large, Open Hydrocarbon...

Industrial Fire Protection

Fire Hazard Calculations for Large, Open Hydrocarbon Fires

Boiling Liquid Expanding Vapor Explosions and Fireball


Presence of Presence of windwind

REVIEWREVIEW

AbsenceAbsenceof windof wind

Pool Fire

Diameter(D)

Flame height(H)

Flame tilt angle(θ)

Radiant heat flux( ) q

Mass burning rate per unit pool area( )m


Main Points

2.1 Basic concepts

2.2 Thermal radiation from fireballs

2.3 Sample problem

2.4 Summary and questions


2.1. Basic concepts

2.1.1 BLEVE(Boiling Liquid Expanding Vapor Explosion)

The explosively rapid vaporization and corres-ponding release of energy of a liquid, flammableor otherwise upon its sudden release from conta-

inment under greater-than-atmospheric pressure at a temperature above its atmospheric boiling point(沸点).

Factory Mutual Research Corporation


Three steps of a BLEVE:fluid

Lost Equilibrium

2.1.1 BLEVE

(1) (2) (3)

saturated vapor

http://upload.wikimedia.org/wikipedia/de/f/f9/Bleve_Gastank.png


Fireball: A burning fuel-air cloud whose energy is emitted primarily in the form of radiant heat.

2.1.2 Fireball


2.1.3 Typical accidents

City State Year

1 Feyzin France 1966

2 Kingman Arizona 1973

3 Texas City Texas 1978

4 Crescent City Illinois 1983

5 Mexico City Mexico 1984


2.1.3 Typical accidents

(1) It occurred on July 11, 1978 in Alcanar, near Tarragona, in Spain.

(2) a BLEVE occurred after a road accident with an LPG truck.

(3） 217 people (including the driver) were killed and 200 more were severely burned.

http://en.wikipedia.org/wiki/File:BLEVE.jpg


Main Points

2.1 Basic concepts


2.3 Sample problem



2.2.Thermal radiation from hydrocarbon fireballs

2.2.1 The BLEVE consequences

Thermal Radiation （热辐射）

Fragmentation （爆炸碎片）

Blast (shock wave) （冲击波）

main hazard


2.2 Thermal radiation from hydrocarbon fireballs

2.2.1 The BLEVE consequences2.2.2 The characteristic parameters of fireball

(1) The maximum diameter(2) The duration of the combustion (3) The surface-emissive power of the fireball

2.2.3 Fireball radiation


1/3fc 8.5 mD

2.2.2 The characteristic parameters of fireball

Where Dc ——maximum diameter，mmf ——mass of fuel，kg

(1) The maximum diameter


For momentum-dominated（动量扩散） fireballs, the burning duration is given by

1/3c f f0.45 for 30,000 kgt m m

For buoyancy-dominated（浮力扩散） fireballs,the burning duration is given by

2.2.2 The characteristic parameters of fireball

1/6c f2.6 for 30, 000 kgft m m

(2) The burning duration


2.2 Thermal radiation from hydrocarbon fireballs

2.2.1 The BLEVE consequences2.2.2 The characteristic parameters of fireball2.2.3 Fireball radiation(1) Point source fireball model（点源模型）(2) Spherical fireball model（球形模型）


Point source fireball model

atmospheric transmissivityradiative

fraction

net heat of combustion

per unit mass

distance from the target to the point

source location

0.67C f

R 22.24

H mq

L

2.2.3 Fireball radiation

http://www.dabaoku.com/gif/154/imagepage/image17.htm


Point source fireball modelRadiative fraction

Where：P ——fuel vapor pressure，MPa

3.0R

0.32R 0.27P

4.0R

fireballs for vessels bursting below relief valve(安全阀) pressure

fireballs for vessels bursting at or above relief valve pressure



Point source fireball modelDistance from the target to the point source location

RT —horizontal distance from the release to the target，m；

ZP —height of the point source，m；HT —target height，m

22T P TL R Z H

Zp

D

L

RTTargetHT



Main Points

2.1 Basic concepts


2.3 Sample problem



2.3.Sample problem

A liquefied propane (丙烷) tank truck whose volume is 6000 U. S. gallons (22.7m3) is involved in a traffic accident, and the tank truck is engulfed(吞没) by fire from burning gasoline. The tank is 90% filled with propane.

Assume that all of propane will contribute to the fireball. Please calculate the radiation effects.


(1) Estimate fireball diameter and duration

f 0.9 22.7 585.3 11,958kgm

1/3 1/ 3c f5.8 5.8 11958 133mD m

1/3 1/ 3c f0.45 0.45 11958 10.3st m


point source model0.67

C fR 22.2

4H m

qL

f

4c

R

11958 kg1

4.636 10 kJ/kg0.4

m

H

6 2 21.7 10 / kW/mq L

(2)Estimate the radiation received at a receptor

Zp

DL

x TargetHTZp

D

L

x TargetHT


Radiation on a receptor from a 6000 gallon propane tank truck BLEVE calculated with point source model

Ground Distance

(m)

Point Source

Radiation(kW/m2)

100 170

200 42

500 6.8

1000 1.7

6 2 21.7 10 / kW/mq L


Effect on Humans from Radiation

Ground Distance(m)

Point Source Radiation(kW/m2)

Effect from Point Source Radiation

100 170 third degree burns, 50% lethality(致死率)

200 42 1% lethality

500 6.8 some pain

1000 1.7 below pain threshold

消防人员及紧急救灾人员最小安全建议距离为4R

人群安全逃脱最小建议距离为15R


Main Points

2.1 Basic concepts


2.3 Sample problem

2.4 Summary


Dc

tc

Point Source Model

2.4 Summary

BLEVE

Fireball

1/3c f5.8D m

1/3c f f0.45 for 30,000 kgt m m

1/6c f2.6 for 30,000 kgft m m

0.67C f

R 22.24

H mq

L


Estimate fireball diameter and duration.

Estimate the received thermal flux .

Calculation Procedure

Determine the thermal impact.


1. Calculate flame radiative heat flux from a 10-m toluene pool fire to a vertical target 2 m above the ground at 12m from the center of the pool with no wind using:

(a) Shokri and Beyler method

(b) Mudan method

2. Illustrate the phenomenon of BLEVE.

3. A storage tank containing with 100 tons butadiene(丁二烯) ruptured, and then caused BLEVE and fireball with heating of external fire, please calculate the fireball diameter and duration, and determine the radiation received by an object normal to the fireball at distances of 100 , 200 and 300 metres from the fireball point (the vapor pressure is 0.4 MPa, the combustion heat of butadiene is 50,409 kJ/kg).

Questions


Fireball radiation(1) Point source fireball model(2) Spherical fireball model

Preview


ReferencesGuidelines for evaluating the characteristics of vapor cloud explosions, flash fires, and BLEVEs.

American Institute of Chemical Engineers. Center for Chemical Process Safety (CCPS).

SFPE Handbook of Fire Protection Engineering (4th ed.). Section 3 Hazard calculations Chapter 11 Fire hazard calculation for large, open hydrocarbon fires.

National Fire Protection Association (NFPA).

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