CSB Findings on Deadly Dust Explosion Prompts Call for National Standard

Dec. 6, 2023
The U.S. Chemical Safety and Hazard Investigation Board reiterates need for a national combustible dust standard in its final investigation report of a fire and explosion at Didion Milling, Inc. in Wisconsin.

On Dec. 6, the U.S. Chemical Safety and Hazard Investigation Board (CSB) released its final report into the deadly explosions and fires at the Didion Milling Inc. dry corn milling facility in Cambria, Wisconsin. The explosion occurred in May 2017 and killed five employees and seriously injured another 14. The incident also ultimately destroyed the facility, resulting in more than $15 million in property damage.

The CSB determined the cause of the dust explosions and collapsed buildings was the ignition of combustible corn dust inside process equipment, which transitioned to multiple explosions. 

A lack of proper equipment safeguards, engineering controls and personal protective equipment; a poor safety culture; and unaddressed combustible dust hazards, in addition to insufficient safety regulations related to hazardous dust contributed to the incident, said the CSB in its report.

According to Trish Kerin, director of the IChemE Safety Centre, in a Chemical Processing podcast, “The company was required to regularly clean the dust accumulation from the inside of the mill not only for safety issues because of combustible dust, but also for food safety and quality issues as well. And they were required to operate and maintain air pollution control devices and have documentation around the maintenance of these things. Now, according to the indictment, they allegedly didn't have a proper log of the important cleaning procedures of the plant... Apparently, according to the indictment, the managers were aware that the cleanings were not getting done.”

The CSB’s findings determined insufficient safety regulations, which cover combustible dust operations. While the Occupational Safety and Health Administration (OSHA) regulates some aspects of combustible dust hazards, OSHA does not have an overarching standard to manage the hazards presented by combustible dust. As a result, Didion was not required to implement safety management systems, such as those required for other highly hazardous materials.

As a result of these findings, the CSB is urging OSHA develop a national regulation for industries that handle combustible dust, as well as increase follow-up inspections when combustible dust hazards have been identified at facilities. Similarly, in its final report, the CSB called on the National Fire Protection Association (NFPA) to update its combustible dust standards to include more comprehensive requirements for dust hazard analyses, incident investigations and management of change.

CSB Chairperson Steve Owens said in a press release, “Combustible dust explosions and fires can be deadly and incredibly destructive. The terrible tragedy at Didion was made even worse due to the lack of important safeguards in the design of the mill equipment and the lack of engineering controls at the facility that could have reduced the potential for serious fires and explosions. Our investigation also determined that Didion had a poor safety culture and inadequate leadership on safety issues that contributed to these tragic circumstances.”

The CSB recommends Didion develop a comprehensive combustible dust safety program, which will include management of change, safety information management, fugitive dust management, management of audits, incident investigations, dust hazard analyses, PPE and emergency preparedness.

Editor’s Note: For more information on hazardous dust control, Chemical Processing recently hosted a roundtable on Combustible Dust Hazard Awareness and Control - Challenges and Successes and issued an ebook covering this topic.

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