The “boom” that rocked Cambria, very late on a Wednesday night seven months ago, continues to reverberate throughout south-central Wisconsin.

Sixteen people were working at Didion Milling when an explosion ripped through the plant at about 11:30 p.m. May 31. Five of them died. Others suffered serious injuries.

As 2017 draws to a close, the cause of the explosion has not been determined. But the federal Occupational Safety and Health Administration has declared that Didion owes more than $1.8 million in fines for safety violations, some of which OSHA officials characterized as “egregious.”

Didion is appealing that judgment, and making plans to rebuild.

There had been a fire at Didion on May 29, two days before the explosion. Although fire inspectors have not determined whether the fire and the explosion were related, OSHA officials cited the fire in a first-floor dryer, and a lack of an automatic fire protection system, as a “serious” violation.

The explosion was heard for miles around Cambria, and it knocked out the village’s electric power.

“I heard the boom, and my house shook,” recalled Cambria Village Clerk Lois Frank.

Fire trucks poured in from around the region — including Madison’s Heavy Urban Rescue Team, a specialized crew of firefighters and paramedics dispatched when buildings collapse and lives are in danger.

Cambria Fire Chief Cody Doucette was on the scene for nearly a full day, and even his familiarity with Didion, and his training in dealing with emergencies there, had not prepared him for what he encountered.

Cambria-Friesland schools — which were not not damaged, despite their location near Didion — were closed the following day, while Superintendent Tim Raymond took stock of the situation, including a decision to hold graduation exercises, as scheduled, the day after in the school gym. (Neighboring school districts had offered to host the Friday ceremony if the Cambria-Friesland buildings had been damaged, but the structures were determined to be safe.)

Although there were no classes, students and staff turned out to make sandwiches for the emergency response workers, some of whom had been at the scene for hours with no break.

The Salvation Army arrived promptly, and a prayer vigil and resource center was set up at Cambria’s First Presbyterian Church.

And the new Columbia County Highway Department shop in Cambria was quickly turned into a venue for families of Didion workers to wait for word on the fate of their loved ones.

The five Didion workers who died as a result of the explosion were Duelle Robert Block, Robert LeRoy Goodenow, Pawel Adam Tordoff, Carlos “Charly” Nunez and Angel Reyes.

In communities throughout the area, people, organizations and businesses organized fundraisers for the survivors, and made numerous other gestures — including the 16 “prayer quilts” hand-made by the Randolph-based Kattywampus Quilt Guild, one for each person who was working at Didion when the explosion occurred.

Didion officials also reached out to area businesses and industries to find places where displaced Didion workers could continue to be employed, with Didion paying their wages.

However, many of the displaced employees had depended on overtime wages as a vital source of their livelihood, and the loss of the overtime meant some of them had to seek help. The Columbia County Health and Human Services Department became a clearinghouse for aid for people affected by the explosion.

The word “rebuild” was first uttered at the first Cambria Village Board meeting following the explosion, on June 5.

Didion officials, including company President Riley Didion, expressed from the beginning their intent to build a new state-of-the-art plant on the same site.

In November — days before the OSHA report was due — the Cambria Village Board invited Didion officials to meet privately with Doucette (who is also a village trustee) and Public Works Director Tom Tietz to outline their proposed concept for rebuilding, before presenting final plans.

How the OSHA findings will affect the rebuilding plans remains to be seen.

In a 45-page report, issued on Nov. 17, OSHA officials declared that the explosion could have been prevented with precautions that are well-known in the corn milling industry.

OSHA cited 14 “willful” violations of safety regulations, eight of which it deemed “egregious” because they were repeated. Five other citations were deemed “serious.” Most involved fire and explosion hazards.

The aggregate fine, more than $1.837 million, is the largest to have been imposed as the result of a single OSHA investigation in Wisconsin. Didion officials are appealing the fine.

Follow Lyn Jerde on Twitter @LynJerde