The U.S. Chemical Safety Board (CSB; www.csb.gov) has released test results confirming preliminary conclusions that two flash fires, which occurred at the Hoeganaes Corp. plant in Gallatin, Tenn., involved the combustion of iron powder that had accumulated throughout the facility and became airborne in combustible concentrations. A flash fire on January 31 killed one worker and seriously burned another. A similar fire on March 29 caused one injury. The Hoeganaes plant manufactures “atomized” iron powder that is sold to the automotive and other industries for the production of metal parts using powder metallurgy.
In the first incident on January 31, two maintenance mechanics on the overnight shift inspected a bucket elevator that had been reported to be malfunctioning due to a misaligned belt. The bucket elevator, located downstream of an annealing furnace, conveyed fine iron powder to storage bins. The two mechanics were standing alone on an elevated platform near the top of the bucket elevator, which had been shut down and was out of service until maintenance personnel could inspect it. When the bucket elevator was restarted the movement immediately lofted combustible iron dust into the air. The dust ignited and the flames engulfed the workers causing their injuries. A dust collector associated with the elevator was reported to have been out of service for the two days leading to the incident.
The second incident occurred less than two months later when a plant engineer, who was replacing igniters on a furnace, was engulfed in combustible dust that ignited. In the course of the furnace work, he inadvertently dislodged iron dust, which had accumulated on elevated surfaces near the furnace. He experienced serious burns and bruises as a result of this second event; a contractor witnessed the fireball but escaped without injury.“Tests conducted on samples of metal powder – collected from the plant – determined that this material is combustible,” said CSB investigator-in-charge Johnnie Banks.
In 2006 the CSB completed a study of combustible dust fires and explosions, which identified 281 incidents that occurred from 1980 to 2005, killing 119 workers and injuring more than 700. The study findings resulted in a recommendation to the U.S. Occupational Safety and Health Administration (OSHA) to develop a standard that comprehensively addresses combustible dust explosions. In 2009, OSHA agreed to develop a combustible dust standard. OSHA is currently in the early stages of the rulemaking process for the standard.
CSB Board member John Bresland said, “Combustible dust is an often overlooked hazard at manufacturing facilities, as CSB investigations back to 2003 demonstrate. Among our open recommendations to OSHA from previous accidents is a call for a comprehensive combustible dust standard designed to protect workers and reduce or prevent dust-related hazards. The CSB will be closely following the discussion at OHSA’s upcoming Combustible Dust Expert Forum on May 13, as regulatory options to eliminate this workplace hazard are reviewed and evaluated.”
The CSB is an independent federal agency charged with investigating serious chemical accidents. The Board makes safety recommendations to plants, industry organizations, labor groups, and regulatory agencies such as OSHA and EPA.