The LEAP building in Farmington was blown apart in a propane explosion Sept. 16, leaving one firefighter dead and seven people injured. Andree Kehn/Sun Journal

AUGUSTA — During the weekend before an explosion disintegrated a nonprofit’s building in Farmington last week killing one and injuring seven, nearly 400 gallons of propane leaked beneath its parking lot, some of it reaching the basement, the State Fire Marshal’s Office said Friday.

Officials weren’t saying what ignited the gas Sept. 16 that sent pieces of the LEAP building on Farmington Falls Road hundreds of feet into the air while four men were in the building’s basement, according to the fire marshal.

Ken Matthews, a propane expert from Raymond, said Friday that because propane is heavier than air, it tends to “settle and pocket” when it leaks.

Matthews, who said he had no specific knowledge about what happened in Farmington, said that gas from a leaking underground line “would have no place to go until it got to the end,” which may mean the building’s basement had a high concentration of the vapor.

It’s possible, he said, that the percentage of gas in the air was so high that there wasn’t enough oxygen present for it to burn until someone opened the door and allowed more air to get in.

Matthews, who helps probe 15 to 20 gas explosions annually around the country, said it doesn’t take much to ignite the gas — even the click of a two-way radio might do it.

In a paper about gas leaks, Scott Kleppe, the president of Sensit Technologies in Indiana, said that “one of the most common and most unpredictable sources of ignition is static electricity, such as the sparks that result when a person touches something after walking across the carpet.”

There has been no hint yet from officials about what might have sparked the explosion in Farmington.

The blast killed a Farmington firefighter on the first floor, Capt. Michael Bell. His brother, Chief Terry Bell, was badly injured while standing near the rear door.

In a statement, the Office of State Fire Marshal said the propane line went from the 400-gallon outside tank at the rear of the property to the basement of the building via an underground section beneath the parking lot.

Investigators said the leaked propane “permeated the ground under the parking lot and some of that gas made its way into the basement.”

“Normally propane has a distinctive odor from an additive added to the fuel,” the fire marshal’s office said, “but investigators think that odor may have been filtered by the soil under the parking lot.”

Texas Propane warns on its website that “when there is an underground propane leak, odor fade can occur. The odorant can be filtered out by the movement of gas through the soil.”

In Farmington, it had enough of that rotten-eggs type odor, though, for a LEAP maintenance worker, Larry Lord, to get everyone out of the building before firefighters showed up in response to a call for assistance.

Matthews said Lord did exactly what he should have done, except for going back inside with the firefighters.

At the time of the explosion, investigators said, Lord was in the basement with three Farmington firefighters, Tim “TD” Hardy, Joseph Hastings and Scott Baxter. Deputy Chief Clyde Ross and firefighter Ted Baxter were outside the building in the parking lot.

Matthews said that typically firefighters arriving on the scene of a gas leak will take readings of the gas concentration in the air before entering a building to make sure the level isn’t so high that it could explode.

He said that when he arrives at a scene similar to what appears to have happened at LEAP, he measures the gas concentration at the front door at head, waist and floor level and then keeps checking as he goes along.

Investigators said the outside propane tank was empty when examined by Lord and another LEAP employee that Monday morning of the explosion. It had been filled Friday by South Paris-based CN Brown Co., which also owned the tank.

Officials have not said publicly who installed the line to the building, which relied on propane to fuel its furnace and hot water heater. The company had no comment on the fire marshal’s report Friday.

The fire marshal’s office statement said it “continues to determine how the line was damaged and what sparked the leaked propane in the building that created the explosion.”

Matthews said there are a lot of possibilities, including corroded older pipes that may have served the original structure on the site.

LEAP, Life Enrichment Advancing People, added a training facility and offices at its 313 Farmington Falls Road that opened this year, connecting them to its existing building.

Another possibility, he said, is that the larger building needed more gas. One way to increase the supply, he said, would be to increase the pressure inside the pipes, perhaps causing them to begin leaking.

The fire marshal’s statement said more than 100 interviews have taken place as the state continues to work with the Bureau of Alcohol, Tobacco, Firearms and Explosives, Farmington police and fire departments and the Maine Solid Fuel Board.

Lord, Baxter and Terry Bell remain in the hospital. The others injured in the explosion have been released.