Inspectors: Filter blew off apparatus before deadly explosion at Didion Milling in Cambria in May 2017

MADISON -- Federal safety inspectors say an air filter blew off a corn grinding device shortly before a deadly explosion demolished a southern Wisconsin corn mill last summer.

Mary Beth Mulcahy

Officials with the U.S. Chemical Safety and Hazard Investigation Board held a news conference Monday, April 30 to discuss preliminary findings laid out in a 13-page report from their investigation into the deadly blast at the Didion Milling Plant in Cambria on May 31. Five workers were killed and 14 were injured.

"To date, we have interviewed almost 40 Didion employees who have all voluntarily given interviews to us, including 10 individuals who shared their personal stories of events that occurred on the night of the incident," said Mary Beth Mulcahy, lead investigator.

CSB investigators spoke with 10 of 14 supervisors. A superintendent told them that he saw the filter blow off the grinder. Flames shot out of the intake line. He fled moments before the plant exploded.

"Shortly before the explosions at Didion, workers reported that they saw or smelled smoke on the first floor of one of the mill buildings," said Vanessa Sutherland, CSB.

"Workers believed that they were dealing with a manageable problem that they were going to be able to solve or they were unaware of the incidents that were occurring in the mill," said Mulcahy.

OSHA, the Occupational Safety Health Administration doesn't have a combustible dust standard, however, there are standards for how combustible dust needs to be handled in different types of facilities to avoid an explosion and other hazards.

"If you look at industry guidance, what you'll find is that it says anything over 1/32 of an inch, which is about the thickness of a dime, could be considered hazardous," said Mulcahy.

Explosion at Didion Milling in Columbia County

Mulcahy said the board's probe is continuing and it could be six months before it issues any conclusions.

CLICK HERE to read the final Didion Milling explosion investigative update

Explosion at Didion Milling in Columbia County