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CSB gives update on fatal Wisconsin grain mill blast

02 May 2018

The US Chemical Safety and Hazard Investigation Board (CSB) held a news conference on April 30 to give an update on its investigation into a grain dust explosion in May 2017, which killed five workers and injured 14 others at Didion Milling in Cambria, Wisconsin.

An aerial view of the Cambria plant after the incident - Image: CSB
An aerial view of the Cambria plant after the incident - Image: CSB

The explosion occurred in Didion’s dry corn milling facility, where raw corn is processed to create a variety of corn products. The dry corn milling process – particularly the acts of grinding and separating individual kernels of corn into distinct components – produces corn dust. Corn dust is combustible and is known to be explosive under certain conditions.
The CSB update presented the perspectives of 10 of the 14 survivors as the events unfolded the night of the incident. The Board determined:
*  Workers believed the conditions at the mill on the night of the incident were “normal,” and up until just moments before the explosions, workers either were unaware of any problems or assumed their troubleshooting efforts would reveal a typical and manageable situation.
*  Prior to the explosion workers reported seeing and smelling smoke coming from the facility.
*  Several workers entered various mill buildings to locate the source of the smoke, but were unable to immediately find the cause.
*  Approximately 15 to 30 minutes before the explosions, workers focused their inspections on a piece of equipment called a gap mill. Workers then observed an air filter blow off of the gap mill’s air intake line, resulting in corn dust filling the air and a three- to four-foot flame shooting from the air intake line.
*  Around 11:00 PM, one or more explosions occurred. The explosions caused the complete collapse of four of the nine buildings that make up the Didion facility; the remaining five were severely damaged.
*  Five workers died as a result of the explosions and the collapse of the buildings. The other 14 workers sustained injuries that ranged from minor to life-threatening. One of the seriously injured had both legs amputated.
The CSB’s full technical analysis of the incident and its examination of dust management at Didion are still underway and will be included in its final report, which will also explore the conditions that influence the safe management of combustible dust and the challenges associated with dust explosion prevention.
Didion issued a statement saying it is committed to the safety of its employees and "is working with industry experts on construction of a new state-of-the-art corn mill, which will feature the latest technology and most effective and safe operational systems available today."
In November 2017, the Occupational Safety and Health Administration (OSHA) said the explosion likely resulted from Didion’s failures to correct the leakage and accumulation of highly combustible grain dust throughout the facility and to properly maintain equipment to control ignition sources. It imposed record fines of $1.8 million on the company.
OSHA cited Didion’s Cambria facility with 14 ‘willful’ – including eight ‘willful egregious’ – and five serious citations, most involving fire and explosion hazards. The company has been placed in OSHA’s Severe Violator Enforcement Program.
“Didion Milling could have prevented this tragedy if it had addressed hazards that are well-known in this industry,” said OSHA Regional Administrator Ken Nishiyama Atha, in Chicago. “Instead, their disregard for the law led to an explosion that claimed the lives of workers, and heartbreak for their families and the community.”
In releasing its update, the CSB also renewed its call for OSHA to set an industry standard for combustible dust to prevent future tragedies.
A previous CSB study identified 281 combustible dust incidents between 1980 and 2005 that killed 119 workers, injured 718, and extensively damaged industrial facilities. The board calls it a critical issue in industrial safety.

The CSB recommended the standard be based on existing National Fire Protection Association dust explosion standards. But CSB chair Vanessa Allen Sutherland says a lack of resources has so far prevented OSHA from acting on the proposal.

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