BELFAST — The State Fire Marshal’s Office has completed its investigation of the March 24 fire that destroyed the Penobscot McCrum plant and ruled the fire “accidental,” but because of the extensive damage, the cause of the fire is undetermined.

According to a revised press release issued just after 3 p.m. Wednesday, March 30, by City Manager Erin Herbig and Fire Chief Patrick Richards, state investigators were unable to determine whether the fire was caused by spontaneous combustion of leftover food or by a mechanical issue.

“The fire started in the area of one of the fryolators, which was located next to a conveyor belt,” the revised press release said.

“The fire then spread directly into the exhaust venting system that exits through the roof and extended into the void space between the ceiling and the roof,” the release said. “This area was located above the fire suppression system,” allowing the fire to travel rapidly into the rest of the building.

The building had many void spaces above the suppression system, which allowed the fire “to spread rapidly under the metal roof,” according to the release. The building was constructed of mixed materials, including masonry, steel and wood framing.

“Given the size of this property, the rapid spread of the fire and imminent threat of hazardous materials, we are so fortunate that all the employees were accounted for early and safe,” Chief Richards said in the release. Controlling and extinguishing the fire were “certainly a team effort,” he said, “and I am grateful for all the Mutual Aid and support that the Belfast Fire Department received throughout this incident.”

Richards said more than 60 first responders were on scene, and they all “went home without any reported injuries,” Richards said.

The fire was reported at 2 a.m. and within a few hours the potato-processing plant was fully engulfed. Employees working during those early morning hours all got out safely. Eleven fire departments battled the blaze along the Belfast waterfront.