The explosion in a Farmington, Maine, human services agency that killed a firefighter and injured seven people last week was caused by a leak in a pipe connecting an exterior propane tank to the building, which allowed propane to seep into the basement, where it pooled until it was ignited, officials said Friday.

Maine authorities said Friday they are still trying to determine how the propane ignited, creating a massive explosion on Sept. 16 that leveled the building that houses LEAP, destroying or damaging several nearby mobile homes and showering the neighborhood with insulation.

Fire Captain Michael Bell, 68, died in the explosion, according to Maine State Police.


In a statement Friday, the Maine State Fire Marshal’s Office said the exterior tank was filled with 400 gallons of propane on Sept. 13, but LEAP employees said the tank was empty the morning of the explosion, three days later.

“Investigators say they located the leak in the propane line, which was buried under the paved parking lot. The line went from an outside propane tank located at the rear of the property, under the parking lot and into the basement of the building,” the fire marshal’s statement said.

“The leaked propane permeated the ground under the parking lot and some of that gas then made its way into the basement. Normally propane has a distinctive odor from an additive that is added to the fuel, but investigators think that odor may have been filtered by the soil under the parking lot,” the statement said.

Investigators have also now determined where each of the eight victims were positioned at the time of the explosion.

“Investigators say Larry Lord was in the basement with Farmington firefighters “TD” Hardy, Joseph Hastings, and Scott Baxter when the explosion took place. Fire Captain Michael Bell was on the first floor, Fire Chief Terry Bell was near the rear door of the building, and Deputy Fire Chief Clyde Ross and firefighter Ted Baxter were outside the building in the parking lot,” the statement said.


Ross, Hardy, Hastings, and Ted Baxter were hospitalized but have been released. Scott Baxter remains in serious condition at the Maine Medical Center in Portland, while Terry Bell, who is Michael Bell’s brother, remains in fair condition at the medical center, according to a statement from the hospital Thursday afternoon.

Lord, a maintenance worker at LEAP, was still in critical condition Friday morning at Massachusetts General Hospital, a hospital spokeswoman said.

Officials have conducted more than 100 interviews during the investigation, the statement said.

The fire marshal’s office, the Bureau of Alcohol, Tobacco, Firearms and Explosives, the Maine Fuel Board, and Farmington police and firefighters are investigating the blast.

Alyssa Lukpat can be reached at alyssa.lukpat@globe.com. Follow her on Twitter @AlyssaLukpat.