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 explosive.

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 close by.

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.

Operators and supervisors who have a clear understanding of the causes of serious injuries and accidents associated with oxygen and fuel gas regulators (i.e., regulator burn-outs, flashback and the dangers of violating the 1/7 rule while using acetylene) will dramatically decrease these occurrences.