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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.
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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 BLEVEs
The 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
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)
TimetoFailure(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.