Acetylene explosion
Robert E. Lowe
Lowe Fire Investigations
San Juan Capistrano, California
Reference is made to “Proper Storage the Key to Acetylene Tank Safety” by Steven Maslansky and John M. Cullen (June 1996). This is an intriguing acetylene explosion many of us will try to solve. Acetylene and propane have similar hazardous properties. Both usually are liquid while in containment. They build pressure or greatly expand with a rise in temperature and are extremely volatile when their gas is free to mix with the atmosphere.
Most of my cases involved recently filled or “packed” tanks. These filling processes usually occurred in a relatively cool atmosphere; then the tanks were exposed to sunlight, warm weather, or an otherwise warmer environment. As the tank (and contents) warmed, the contents compressed to build pressure, causing a relief valve to function. This provided the necessary relief for the tank to prevent a boiler-type explosion, but the expelled gas or vapor can explode if an ignition source is present. Without an ignition source, the relief valve reseats as pressure is relieved. There usually is no problem if the expelled product is dispersed outdoors.
Sometimes, as in the acetylene tank safety article, there is a flash fire or explosion with no obvious ignition source.
Fires and serious injuries have resulted, especially with propane, when attendants are filling tanks and a leak develops. Ignition has occurred even when the usual ignition sources (smoking, pilot lights, switches, etc.) can be eliminated.
The culprit (ignition source) usually is a static spark. This came to my attention some years ago when a series of accidents occurred. Tanks had been filled and left outside, exposed to warm weather. This was the common scenario: The pressure relief valve functioned. A bystander (victim) went to the tank to investigate. A flash fire burned the victim`s face, arms, and hands.
In three such cases, the victims survived. Each one told the same story: A loud hiss and a vapor cloud attracted them to the tank. A “flash” and intense heat when they arrived were the last things recalled.
Before interviewing the third victim, I could visualize his appearance even before entering the hospital room. As expected, he was on his back swathed in bandages with both arms suspended in an arch over his chest. What could be seen of his face was coated with medication.
This last victim had been filling acetylene tanks at a cryogenics facility. He heard the hiss and observed a vapor cloud. He approached carrying a wrench. The flash occurred as he reached the tank. He miraculously escaped with his life when he ran clear. The loading rack was a disaster area.
The only ignition source that could not be eliminated was a static electrical spark. This static charge was evidently coincidental with the escaping gas.
Further research confirmed that fluid escaping through an orifice under pressure will generate an electrical charge. This is true even of steam. This information helped solve several subsequent “mystery” ignitions of similar volatile products.
There is no reference to this phenomenon in fire investigation books and articles I have read so far. It will help to hear from others on these types of incidents.
