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Torch Safety(From the Nov/Dec 1998 issue of Demolition, published by the NADC)
Acetylene Combined with Pure Oxygen can be a Deadly Mix
without the Proper Training
By Steve Ababan, General Manager- Torchmaster Carlsbad, CA
How dangerous is acetylene when mixed with pure oxygen?
Obviously, the answer to this question is relative to various
conditions. Few other products with such inherently dangerous properties
are as available to the general public as acetylene. Yet, most people who
use acetylene have received only rudimentary training on its safe use.
This training usually does not provide them with sufficient information to
protect themselves and others from serious injury.
Under high pressure (pressures above 15 psig) pure acetylene
can decompose violently with the evolution of heat. Shock, high
temperature or a reactive substance can initiate decomposition, and oxygen
is not required to either initiate or sustain this decomposition. The
higher the pressure, the smaller the initial energy input required to
cause decomposition. Therefore, it is vitally important to remember that
acetylene is unstable at pressures above 15 psig, and without a properly
functioning acetylene regulator to control outlet pressure, there is a
real danger of a serious accident.
Because it provides the highest degree of heat on a smaller
area, acetylene is the most commonly used fuel gas in our industry.
Acetylene is the gas of choice when wanting to avoid warping (undesired
twisting or bending from high heat) while cutting metal. Like any other
fuel gas, when combined with pure oxygen, acetylene becomes violently
A balloon two inches in diameter containing equal parts of
acetylene and pure oxygen has the explosive force of one quarter of a
stick of dynamite. This is enough force to cause serious injury to anyone
Inflating this two-inch balloon, with the same mixture, to a
nine-inch diameter increases the explosive force 80 times. That equals
twenty sticks of dynamite. Now, consider the fact that it is not uncommon
to see 100-foot sections of oxy-fuel gas hose being used on jobsites or in
metal shops. A common inside diameter of oxy-fuel gas hose is 1/4 inch. If
you calculate the volume of 100 feet of hose with an inside diameter of
1/4 inch, you'll find the volume is equal to the 9-inch diameter balloon.
This means, should oxygen enter the fuel gas hose or should fuel gas enter
the oxygen hose, a mixed gas explosion with the force potential of 20
sticks of dynamite could occur.
It is therefore vital to stress the importance of having and
maintaining properly functioning oxygen gas equipment. Reverse flow check
valves and flashback arrestors, properly positioned and installed on your
equipment, provide protection from mixed gas explosions occurring
upstream. Because mixed gas explosions are potentially the most
devastating of all oxy-fuel equipment accident, these properly functioning
reverse flow check valves and flashback arrestors are essential and should
be checked often.
Of equal importance is to ensure that every operator and
supervisor in your company is properly trained in all areas of oxy-fuel
gals equipment operations and safety and can identify and react to all of
the conditions associated with the causes of serious accidents.