The U.S. Chemical Safety and Hazard Investigation Board (www.csb.gov) issued a warning to acetylene producers saying they should take special precautions when handling acetylene, a highly explosive gas used in welding and cutting metals.

The safety bulletin was issued by Chemical Safety and Hazard Investigation Board on Jan. 26, a year after an explosion killed three workers and injured a fourth at the Acetylene Services Co. (ASCO) in Perth Amboy, N.J.

Investigators concluded that several factors resulted in acetylene flowing backward from the company's production generator through water pipes and out of an open drain valve into a shed. The board said gas built up to a dangerous level and probably was ignited when it reached the shed's propane space heater.

Three workers shoveling snow near the shed were killed in the blast, and a fourth worker was seriously injured.

"The tragic accident at ASCO points to how important it is to have comprehensive operating procedures, to train workers in those procedures, and to have effective measures in place to prevent the backflow of flammable gases," Gary L. Visscher, a member of the Chemical Safety and Hazard Investigation Board said in a press release.

"The Chemical Safety and Hazard Investigation Board is urging acetylene producers and handlers to review the safety bulletin and examine their systems and safety procedures to prevent this kind of accident from occurring again," Visscher said.

The bulletin urges operators to maintain up-to-date operating procedures; use checklists; relocate vents to safe, outside locations; test critical valves and ensure that enclosures, such as sheds that contain hazardous materials, meet national fire code standards.