Probe reveals possible cause of fatal explosion
Occupational health and safety professionals may be troubled by the results of a joint investigative report on the origin and cause of the Feb. 25, 1999, explosion at the Jahn Foundry in Spring-field, MA. The report, released recently by the Occupational Safety and Health Administration suggests a deadly hazard could be overlooked in industrial ventilation systems.
According to Ronald Morin, OSHA area director in Springfield, the Joint Foundry Explosion Investigation Team was composed of OSHA, the Massachusetts Office of the State Fire Marshall, and the Springfield Arson and Bomb Squad.
Cooperative effort to discover the cause
He notes that these three agencies undertook a cooperative, joint investigation into the cause of the explosion and fire, which extensively damaged several buildings in the Jahn Foundry complex and seriously injured 12 employees. Three of the most severely burned employees subsequently died from their injuries.
"Our goal was to determine, as best we could, the conditions which existed in the foundry prior to the explosion and the events leading up to this catastrophic accident in order to prevent anything like this happening again," Morin says. "It is hoped that the release of this report on the findings of the joint investigation will allow other foundry facilities across the country to assess their own situations and apply the lessons learned here in time to prevent a similar tragedy."
He notes the investigation determined that "an initiating fire event" in one of the shellmMold stations in the shell mold building was pulled into the exhaust ventilation system. The interior of the ductwork of that system was heavily loaded with deposits of phenol formaldehyde resin, an explosive organic dust. The ignition of this dust caused a turbulent fire and explosion(s) that traveled through the interior ductwork. The explosion(s) in turn shook down explosive concentrations of combustible resin dust that had collected on surfaces throughout the shell mold building.
When the fire exploded out from the ductwork, it ignited these airborne concentrations of combustible dust, which caused a catastrophic dust explosion that lifted the building’s roof and blew out its walls.
Two scenarios
The report noted that, although it was not possible to conclusively determine the initiating event that caused the resultant dust explosion, several plausible scenarios were developed from the physical and testimonial evidence. Of these, the following two were determined to be the most probable:
• Dust scenario.
Heavy deposits of resin dust were found in the flexible exhaust ducts serving the ovens in the shell molding stations. The open ends of the ducts were placed adjacent to the ovens, at approximately head level, and in an area where employees must present themselves to deal with the ovens.
Jarring of the duct readily dislodged the deposits of dust. In this scenario, jarring of the duct caused dust to fall down onto the oven and be ignited. The resulting fireball was then pulled back into the flexible duct, where it started the turbulent fire and explosions in the exhaust ventilation system.
• Gas scenario.
The fuel trains to the ovens in the shell molding stations were found to be in very bad condition. The internal mechanisms of the valves controlling the flow of combustion air and natural gas to the ovens were massively contaminated with resin and sand. The proper functioning of these valves was critical for providing air and gas to the ovens in the correct ratio to support combustion. Oven flameouts were a recurrent problem. The ovens were not provided with a flame-sensing device to prevent the flow of gas to the oven in the absence of a main flame.
Although a switch and thermocouple prevented the flow of gas to the oven in the absence of a pilot flame, the pilot flame was not able to light the burners. Thus, in the absence of a main flame, gas could continue to flow to the oven. In this scenario, gas was flowing to an oven that was not lit. The unburned gas collected in sufficient quantities to finally be ignited by the pilot or other ignition source. The resulting fireball was pulled into the flexible duct, where it started the turbulent fire and explosions in the exhaust ventilation system.
In either the dust or gas scenario, the report found that inadequate housekeeping, ventilation, maintenance practices, and equipment were all causal factors for the initiating and catastrophic events.
The 56-page report is available for free by contacting one of the following:
• Occupational Safety and Health Administra-tion, 1441 Main St., Room 550, Springfield, MA 01103. Telephone: (413) 785-0123.
• U.S. Department of Labor, JFK Federal Building, Office of Public Affairs, Room E-120, Government Center, Boston, MA 02203. Telephone: (617) 565-2072.
You have reached your article limit for the month. Subscribe now to access this article plus other member-only content.
- Award-winning Medical Content
- Latest Advances & Development in Medicine
- Unbiased Content