December 14, 2023

CSB Report on Explosions, Fire Highlights Combustible Dust Concerns

Lack of recognition of combustible dust hazards contributed to a deadly fire and series of explosions in May 2017 at the Didion Milling Inc. facility in Cambria, Wisconsin, according to a report (PDF) by the Chemical Safety and Hazard Investigation Board (CSB). On May 31, corn dust ignited inside the milling facility’s processing equipment. The fire led to multiple explosions that fatally injured five employees, seriously injured 14 others, and destroyed the facility. CSB’s investigation of the incident determined that Didion had not recognized or addressed hazards posed by combustible dust. The report calls on Didion to address safety issues that contributed to the incident, OSHA to promulgate a combustible dust standard, and the National Fire Protection Association to update its existing standards for combustible dust.

On the night of the incident, employees at the facility smelled smoke and began an investigation to locate the source. Two employees were inspecting milling process equipment in one of the buildings when they heard an explosion and observed flames emanating from a pipe. According to CSB’s report, the employees recognized that the dust cloud in the air above the flames was likely to explode and immediately left the building. They attempted to use their radios to warn other employees of the emergency and the need to evacuate, but, due to conflicting traffic on the radio channel, they were unable to do so before a second, larger explosion occurred. The fire spread rapidly through the interconnected dust collection systems of the milling process equipment, resulting in subsequent explosions throughout the facility.

As a result of insufficient assessment of combustible dust hazards, Didion’s design processes lacked safeguards and did not follow design practices that could have prevented the incident or reduced its severity, CSB found. The company had not installed engineering controls to prevent or mitigate combustible dust hazards. CSB also cited Didion’s neglect to provide personal protective equipment to employees, poor safety culture and leadership, and failure to act on the findings of previous investigations, inspections, and audits, despite several previous fires.

The grain industry is one of several affected by combustible dust fires and explosions. Although OSHA regulates some aspects of combustible dust hazards, the agency lacks an overarching standard for managing them. “As a result, Didion was not required to implement safety management systems, such as those required for other highly hazardous materials,” CSB stated. CSB recommends that OSHA develop a national standard for industries that handle combustible dust and increase follow-up inspections at facilities where combustible dust standards have been identified.

More information may be found in CSB’s press release.