Acetylene Explosion cont'd

DOE-HDBK-3010-94

7.0 Application Examples; Production Support Lab Example

In this test, acetylene in an explosion chamber is connected to the acetylene cylinder.

The acetylene in the chamber is detonated, and the detonation propagates into the

cylinder. The test passes if there are no cracks or swelling in the cylinder after 24

hours. Industrial literature on the subject of cylinder stability notes:

For some reason, acetylene has retained an image of danger and

accident proneness which it does not deserve. Modern methods of

cylinder construction and porous mass manufacture have produced

cylinders which resist standard bonfire tests and tests in which a torch

is played on the cylinder wall until it bulges with red heat. With

regard to shock, a generally believed hazard, cylinders have been

dropped from 40 ft and even from aircraft without incident. They have

punched their way through concrete floors when accidentally dropped

from the top of construction sites.

Accordingly, the accident in question for this event is not a catastrophic detonation of

the cylinder contents. That is why the large fire scenario examined did not consider

an acetylene explosion a common cause consequence of the fire. Acetylene cylinders

are not high-pressure cylinders at ambient conditions. The response to large fires is

for a fuse plug in the cylinder to melt, after which acetylene gas ignites and forms a

visible jet torch emanating from the fuse plug. The bottle eventually empties the

acetylene contents, with the depletion rate a function of the rate at which acetylene

comes out of solution with acetone, not a function of pressurized gas flow through a

nozzle.

The acetylene explosion of concern is an explosion external to the cylinder. If

acetylene leaks from the bottle, it can form a flammable vapor cloud like any other

flammable gas. Discounting equipment, the total volume of the atomic absorption

unit room is ~ 2000 scf. If the entire content of the acetylene cylinder (125 scf) is

uniformly distributed throughout this volume, the resulting acetylene concentration by

volume is ~ 6%, which is above the lower flammable limit for acetylene in air

(2.5%). Exceeding the lower flammable limit means an acetylene deflagration is

physically possible. Typical building ventilation flow and the physical inability of the

cylinder to rapidly void its contents, however, make such an explosion an unlikely

event. It would not, under any circumstances including the unlikely development of a

flammable gas cloud in the glovebox, merit modelling as a confined condition with

progression to detonation.

The exact strength of the explosion is of interest only for estimating the degree of

physical damage to the overall facility. It is of interest in source term determination

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