Combustible Metal Dust Cause of Fires

Monday, May 16, 2011 @ 12:05 PM gHale


Test results confirmed two flash fires that occurred at the Hoeganaes Corp. plant in Gallatin, TN, with one fatality, involved the combustion of iron powder which had accumulated throughout the facility and became airborne in combustible concentrations.

A flash fire January 31 killed one worker and seriously burned another. A similar fire occurred March 29 and caused one injury, said the U.S. Chemical Safety Board (CSB).

The Hoeganaes plant, which employs 175 workers, manufactures “atomized” iron powder which they sell to the automotive and other industries for the production of metal parts using powder metallurgy.

The first incident occurred January 31 as two maintenance mechanics on the overnight shift inspected a bucket elevator that was malfunctioning due to a misaligned belt. The bucket elevator, located downstream of an annealing furnace, sent fine iron powder to storage bins. The two mechanics were standing alone on an elevated platform near the top of the bucket elevator, which they shut down until maintenance personnel could inspect it. When they restarted the bucket elevator, 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 out of service for the two days leading to the incident.

The second incident occurred March 29 when the combustible dust engulfed a plant engineer, who was replacing igniters on a furnace, and it 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.

“The team observed significant quantities of metal dust on surfaces within close proximity to the incident locations. This was of particular concern as metal dust flash fires present a greater burn injury threat than flammable gas or vapor flash fires. Metal dust fires have the potential to radiate more heat and some metals burn at extremely high temperatures in comparison to other combustible materials.” In addition to visible dust particles in the air, investigators saw 2 to 3-inch layers of dust on flat surfaces, rafters, and railings throughout the facility.

In the course of reviewing company documents, Banks said last year Hoeganaes submitted 23 dust samples from the Gallatin facility to an independent laboratory for testing and 14 were combustible. Furthermore, investigators found the facility had documented multiple reports of flash fires during repairs on furnace belts at their facility located in Cinnaminson, NJ, which resulted in two injuries in 2000 and one fatality in 1996.

“The presence of combustible dust was known by Hoeganaes at the times of the accidents; it appears the risks were not adequately addressed by the company,” Banks said.

The CSB investigation will examine the company’s dust prevention efforts at the facility and its compliance with the National Fire Protection Association Standard 484 that details requirements for dust collection systems, dust cleaning frequency, and building construction and egress provisions.

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.

“Combustible dust is an often overlooked hazard at manufacturing facilities, as CSB investigations back to 2003 demonstrate,” CSB Board Member John Bresland said, “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.”



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