CSB releases video on combustible dust explosion at Didion Milling

The U.S. Chemical Safety and Hazard Investigation Board (CSB) released a new safety video this week on its investigation into the 2017 combustible dust explosions and fires at Didion Milling in Cambria, Wisconsin.

Five employees were killed in the incident, and 14 others were injured. The incident also destroyed the facility, resulting in over $15 million in property damage.

The CSB's new safety video, Deadly Dust: Explosions at Didion Milling, includes an animation of the events leading to the incident, commentary from CSB Board Member Sylvia Johnson, and commentary from CSB Investigators Melinda Hartz and Cruz Redman.

Corn grinding process completely destroyed

Didion Milling is an agricultural processing company with several facilities based in Wisconsin. At Didion’s Cambria dry corn mill, corn kernels were ground into smaller components for use in a variety of corn-based products.

The process of grinding corn kernels produces corn-based products and dust as a byproduct. The CSB’s investigation found that both the product and dust can be combustible.

Shortly after 10:30 p.m. on May 31, 2017, multiple employees at the Didion facility noticed an unusual smell or saw smoke. The CSB determined that the smoke was likely coming from a “smoldering nest” of dust, located inside the corn grinding process.

The smoldering nest ignited, leading to a combustible dust explosion within milling equipment and fires that spread to other areas of the facility. After the explosion shockwave reached a dust collection system that connected to process piping throughout the entire facility, secondary explosions spread throughout the mill buildings.

Video discusses five key safety issues

The CSB released its final report on its investigation in Dec. 2023. The new safety video covers five of the 13 key safety issues identified in the CSB’s report that contributed to the incident:

1. Process hazard recognition
2. Dust hazard analyses
3. Fugitive dust management
4. Process safety leadership
5. Regulatory coverage of combustible dust

The video also highlights safety recommendations made by the CSB to Didion Milling, the National Fire Protection Association (NFPA), and OSHA.

Among other important issues, the CSB’s report and the new video point out that since 2006, the CSB has called on OSHA to develop an overarching standard on combustible dust for general industry. OSHA has yet to issue a general industry combustible dust standard.

“The CSB has been calling for a comprehensive standard on combustible dust for many years to help prevent tragic, deadly incidents like the one at Didion from continuing to occur,” Johnson said. “Robust regulation is absolutely essential to keep these incidents from happening in the future.”