A fatal May 2017 explosion at a dry corn milling facility in Cambria, Wisconsin occurred because the company didn’t recognize the hazards posed by combustible dust.
The U.S. Chemical Safety and Hazard Investigation Board (CSB) also found that the severity of the incident, which killed five workers and injured 14 others, was due to the company’s failure to evaluate the risk of fires and the need for flame-resistant PPE.
5 killed, 14 injured, facility destroyed
On May 31, 2017, employees at the Didion Milling Facility smelled smoke in parts of the mill during normal operations.
They traced the source of the smoke to a location on the first floor of one of the buildings. While investigating some processing equipment, several of the employees heard an explosion and saw fire coming from piping on the rotary gap mill equipment discharge.
The employees who witnessed the explosion and fire began evacuating and attempted to notify other employees about the emergency via radio. However, there was some confusion caused by conflicting radio traffic.
At the same time, a fire began spreading through the process equipment via the facility’s interconnected dust collection system, which resulted in secondary explosions throughout the facility. Employees who weren’t in the area where the explosion and fire were first observed didn’t realize there was an emergency. They weren’t aware of the need to evacuate.
This resulted in the deaths of five workers and serious injuries for 14 others. The explosions destroyed the facility, doing more than $15 million in property damage.
‘Several issues contributed to severity of incident’
CSB investigators determined that the explosions were caused by the ignition of combustible corn dust inside the process equipment.
The investigation found that Didion failed to:
- recognize the hazards posed by combustible dust throughout the milling process, resulting in the company’s failure to understand or address the hazard
- evaluate the risk of fires and its employees’ need for flame-resistant PPE, and
- investigate prior incidents at the mill and take corrective measures to prevent a recurrence.
“The CSB’s investigation found several issues which contributed to the severity of this incident,” Investigator-in-Charge Cruz Redman said. “They include a lack of hazard recognition, a failure to provide proper engineering controls, and a failure to implement safety management systems to mitigate combustible dust hazards which could ultimately impact the safety of all the workers at the facility.”
CSB: OSHA should develop regs for combustible dust
Following the investigation, the CSB made recommendations to Didion, federal OSHA and the National Fire Protection Association (NFPA).
The CSB said that Didion should develop a comprehensive combustible dust safety program, including:
- management of change
- safety information management
- fugitive dust management
- management of audits
- incident investigations
- dust hazard analyses
- PPE, and
- emergency preparedness.
For OSHA, the CSB recommended development of a national regulation for industries that handle combustible dust. Further, follow-up inspections should be conducted when combustible dust hazards are identified at facilities.
Federal OSHA currently regulates only some aspects of combustible dust hazards but doesn’t have an overarching standard to fully address the issue. This is why Didion wasn’t required to implement safety management systems like those required for other hazardous materials.
The CSB also called on the NFPA to update its combustible dust standards “to include more comprehensive requirements for dust hazard analyses, incident investigations, and management of change.”