Investigators have determined the fire that destroyed the Penobscot McCrum potato processing facility on the Belfast waterfront was accidental, but the cause remains undetermined because of the extent of the damage.

The March 24 fire engulfed the building on Pierce Street and prompted road closures, evacuations and a shelter-in-place order as crews worked to bring it under control. No one was injured.

The Maine State Fire Marshal’s Office investigated the fire but was unable to determine if it was started by spontaneous combustion of leftover food or a mechanical issue, according to city officials.

The fire started near a fryolater located next to a conveyor belt. It spread quickly into the exhaust venting system that exits through the roof and extended into the space between the ceiling and metal roof. That area was located above the fire suppression system, allowing the fire to spread rapidly into the rest of the building, according to officials.

“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,” Belfast fire Chief Patrick Richards said in a statement. “Control and extinguishment of this fire was certainly a team effort, and I am grateful for all the mutual aid and support that the Belfast Fire Department received throughout this incident. There were more than 60 first responders on scene that went home without any reported injuries.”

The facility employed 138 people and was one of Belfast’s largest employers. Gov. Janet Mills pledged to help the city, company and employees recover. The Maine Department of Labor’s Rapid Response Team is providing employees resources such as unemployment compensation if needed, the administration said.

The McCrum family represents five generations of Maine potato farmers dating to the northern Maine town of Mars Hill in 1886. The family started processing its own potatoes in Belfast in 2004 after purchasing Penobscot Frozen Foods. They also opened a new processing facility in Washburn in June 2020, according to the company website.