During a six-month period, a company that produced iron powder for use in manufacturing metal parts had a series of three flash fires and deflagrations, the first two involving powdered iron and the third involving hydrogen gas and powdered iron. These incidents resulted in a total of 5 fatalities and injuries to several additional personnel.
The plant operated by reducing iron oxide to elemental iron in furnaces with a hydrogen atmosphere and fired by natural gas. The iron is then milled to a fine powder.
The first incident occurred when maintenance personnel were adjusting a bucket elevator at the end of one of the furnaces. As part of the adjustment, they requested the line operator jog the elevator. When this occurred, iron powder was suspended in the air and ignited. Both operators were severely burned and subsequently died from their injuries.
The second incident occurred when maintenance personnel were performing maintenance on a burner for one of the furnaces. While attempting to reconnect a natural gas hose on the burner they banged on the hose connection with a hammer. This lofted dust collected on the furnace into the air which was ignited by an adjacent burner. One of the workers was engulfed by the ensuing fireball.
The third incident occurred when operators heard gas leaking in a drainage trench under the end of the furnaces. While maintenance personnel were removing trench covers to investigate the source of the leak, fugitive hydrogen gas ignited. The deflagration from the gas cloud lofted iron powder that had accumulated on nearby surfaces which also ignited. The fireball fatally injured three employees.
ESi was retained to investigate the origin and cause of each incident.
A finely divided combustible particulate solid presents a fire or explosion hazard when suspended in air or the process-specific oxidizing medium over a range of concentrations. Many of these combustible dusts create an initial fireball, generating subsequent fires or explosions, potentially propagating to large portions of a facility. Therefore, ESi’s investigations initially focus on identifying the combustibility of the dust. The investigation included site visits where the equipment involved was examined, employees and witness were interviewed, and iron powder samples were collected. The sample taken was subjected to a screening test to determine combustibility. ESi’s testing showed that the powder was combustible , but with a slower burning velocity. . These findings were consistent with eye witness observation that in each incident, dust clouds at the plant ignited but did not propagate beyond the initial dust cloud. In each of the instances investigated at this plant, ignition of the initial dust cloud did not result in additional dust being lofted, so the fire did not propagate throughout the plant.
ESi investigated each incident, identifying how the dust was lofted or how the gas leak occurred, and how the dust and gas were ignited. Inadequate cleaning of fugitive iron powder and inadequate maintenance of equipment contributed to the cause and the severity of the incidents. The company responded by retaining ESi to audit each of their plants to identify equipment or hazardous conditions that needed repair, or other rectification. ESi’s audit identified numerous items at each plant that needed attention. ESi also recommended several items for the company to redo a hazard analysis and consider improving their equipment design, safety systems, and procedures.
Short summary:
A plant that produced iron powder for use in manufacturing metal parts had a series of three flash fires and deflagrations within a 6-month period, resulting in a total of five fatalities. ESi was retained by the company to investigate each incident. In each case, ESi was able to identify the fuel for the flash fires (fugitive iron dust and leaking hydrogen ), the likely ignition source, and the scenario that resulted in the flash fire or deflagration. As a result of ESi’s investigation, the company asked ESi to perform an audit of their remaining plants to identify unsafe conditions and recommend corrections or repairs to eliminate or control hazardous conditions found.
