bleve

1Safety Control Dept.

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The phenomenon known as a Boiling Liquid Expanding Vapor Explosion (BLEVE) is the result of a liquid within a container reaching a temperature well above its boiling point at atmospheric temperature, causing the vessel to rupture into two or more pieces. A BLEVE can occur when fire impinges on the LP tank shell at a point or points above the liquid level of the contents of the LP tank. This impingement causes the metal to weaken and fail from the internal pressure. 2Safety Control

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Rev. - 0 3Safety Control Dept.

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BLEVEs can result from mechanical damage to a tank, as well. This damage can be the result of a train derailment, traffic accident, or other physical shock.

In these cases, the BLEVE generally occurs simultaneously with impact. When a BLEVE occurs, debris may travel hundreds of feet, with tremendous force, and the escaping fuel can ignite causing an expanding fireball.Although most liquefied gas BLEVEs that involve container failure result from fire exposure, a few BLEVEs have occurred due to container failures from other causes, such as corrosion or impact from an outside force.


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(A) Two-Step Slow BLEVE

First a small hole forms in the vapour space wall

and this leads to a pressure drop which

then causes a liquid boiling response that

causes pressure

recovery in the tank.


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This pressure recovery drives the crack along the length of the tank to cause the total loss of

containment and BLEVE

The crack velocity may be as low as 1 m/s.


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In this case there is a significant time between when the original fissure opens and when the tank fails catastrophically.


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(B) Single-Step Rapid BLEVE The BLEVE of a

400 liter propane tank exposed to

torch fire impingement. (non- ASME

code) The tank has a 3 mm wall rather than the 6 mm.


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This tank failed so rapidly that the liquid flashing had little or no role in the tank failure.

The vapour energy was sufficient to drive the failure crack the full length of the tank.


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In this case the crack velocity was of the order of 150 m/s.


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(C) Transient Jet Release

If the tank has not been weakened sufficiently then a BLEVE does not take place after thermal rupture is

initiated.The fissure does not run the entire tank length but is arrested in strong material.


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The tank contents vent as a two-phase transient jet. If the hole is large (i.e.,

the hole length is of the order of the

tank diameter) then the release looks very much like a BLEVE (i.e., all

contents vent in a fraction of a

second, large fireball, tank may

rocket).


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Fireballs from BLEVEsThe shape and liftoff of BLEVE fireballs vary

significantly and depend on the detailed thermodynamic state of the liquid, and the

details of the tank failure.

1) If the tank fails rapidly then

classical spherical fireballs result.


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2) If the failure is slow then the initial jet release sends the fireball high in to the air.


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3) If the liquid is relatively cool then a large ground fire is possible. These differences can change the hazards to nearby objects (such as emergency responders) significantly.


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Suggested Safety Distances For Propane or LPG Tank Size for

BLEVE

Tank Capacity (Liters)

Distance (M)

1 10 100 1000 10000 100000 1000000

4R (R=fireball radius) working distance for firefighters and emergency responders. It must be stressed that at 4R personnel will still be exposed to some projectile threat. A distance of 15R is suggested as a minimum for the evacuation of the public.


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Time to Failure vs Capacity & Fire Type(Propane, initial fill 80%, PRV flow based on 20%

engulfment)

Tim

e to

Fai

lure

(Min

)

Tank Diameter (M)The tanks are not equipped with thermal barriers or water spray

systems.


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Emergency Response Planners

To estimate hazards and plan response tactics. Study likely fire scenarios and plan evacuation procedures.

Engineers and Managers

Plant designer can fine tune plant layout. Study various accident scenarios and use this information to assist in the planning for minimal damage.


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The questions should include: is life or property at stake ? what was the time to respond ? how long has the fire been burning ? how big is the tank? is the tank thermally protected? what is the fire contact type and severity ? what are the wind conditions ? what is the ground topography ? are there other tanks or hazards? are there confining structures ?

Step by Step Input.


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Estimate the hazards including: BLEVE blast BLEVE fireball projectiles and tub rockets Vapour cloud explosions (VCE)

From this critical advice given on: responder command position fireball damage vs distance blast damage vs distance expected projectile ranges possible VCE blast vs distance recommended evacuation distances effects of wind cooling water flow rates cooling water supply

BLEVE Hazards Prediction.


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Case Study:

On the morning of June 27, 1993 at 9:02 a.m.,

The Warwick - Canada, Volunteer Fire Department responded to a report of a barn fire.

When they arrived at approximately 9:12 a.m. The fire department found a large cattle barn ablaze. During the size-up phase, a 4000 liter (1055 gallon) propane tank was found close to the involved barn.

The relief vents were operating on the tank shooting flames over five meters (16 ft.) into the air.


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Case Study: Cont...

Fire fighters began to apply water to the exposed LP tank in an effort to cool it.

Suddenly, the tank BLEVE'd and split into two large pieces.

The blast sent one of the pieces into an open field,

While the other piece traveled over 45 meters (150 ft.), and struck a fire engine, and continued another 230 meters (754 ft.) where it struck a vehicle parked on the road trapping an occupant.


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Case Study: Cont...

Three fire fighters were killed when the piece struck the engine, where they were donning protective equipment and preparing hoselines.

The fourth fire fighter was killed when he was thrown approximately 45 meters (150 ft.) as the LP tank part slammed into the engine.

The blast also injured three fire fighters as well as four civilians, including an occupant in the vehicle on the road.


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Controlling an LP-Gas leak and/or fire the following three methods of control should be utilized:

1. If there is a leak with no fire present,

- the flow of gas should be slowed or stopped.

This action is appropriate when the flow can be controlled,

through intact valves or control devices, and by personnel

that are trained in the operation of the control devices.


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2. Dissipating gas vapors through ventilation or the application of water streams to prevent the vapors

from reaching a flammable mixture within the

flammable range.


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3. Applying water to exposed containers and equipment to cool them and prevent failures and BLEVEs from occurring.

The major consideration for this method is the availability of an adequate water source for the constant and long-term application of water to the exposed equipment. The amount of water required is dependent on the size of the leak or fire and its location.

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