The propane heating system in the building that exploded in Farmington this week had been problematic for months, according to an official there, and people who lived behind it said they had been smelling gas for weeks.

The two-story building that housed the nonprofit LEAP Inc. exploded Monday, killing fire Capt. Michael Bell, 68, and critically injuring four other people, including the maintenance manager who noticed the propane smell, evacuated the 10 employees inside and called the fire department. Most of the mobile homes next door also were destroyed in the blast, which shot debris 200 feet in the air and was heard for miles.

Scott Landry, a town selectman and state representative who sits on LEAP’s board of directors, said the heating system had been malfunctioning since the building’s expansion was completed in May, though he was not certain exactly what the problem was. He said he believed fire officials had been there to check things out.

“With today’s technology, I don’t know how we didn’t know about that leak before Monday,” he said.

The investigation into the explosion’s cause will continue into next week. The State Fire Marshal’s Office cleared the scene Thursday.

Asked Friday whether fire officials had been called to the building before Monday’s explosion, Maine’s public safety spokesman, Stephen McCausland, said he didn’t have that information.

“That’s obviously something investigators would be looking at,” he said. “Anything involving that building is going to be looked at.”

Some of the residents of the mobile home park behind the LEAP building said they had smelled propane for weeks.

Betty and Shannon MacLean, who lived in one of the homes, said they didn’t report the odors to anyone because they had made previous complaints about trash and didn’t want to stir up more issues.

“I hollered at the construction people that worked there, but that’s all I did,” Shannon MacLean said. “(We’ve smelled it) on and off since they built it.”

Added Betty MacLean: “The only reason I didn’t call them about the smell was because I had called them about the trash that was left behind during the construction.”

Three other residents said they too had been smelling gas but didn’t want to give their names.

However, one resident of the mobile home park, Maggie Camilleri, said in a phone interview Friday night that she hadn’t noticed any gas smell in the weeks leading up to the explosion Monday. Calls to Randy Dean, the park’s landlord, went unanswered Friday night.

Franklin County Sheriff Scott Nichols, whose department oversees the emergency dispatch center, said he didn’t know whether there had been previous fire calls to the LEAP building. C.L. Folsom, the emergency communications director, did not return a call Friday.

Darryl Wood, executive director of LEAP, declined to answer any questions about the building.

“I have been asked by the fire marshal not to discuss the events of that morning until their investigation is complete,” he said in an email.

Town records show that the LEAP building, on Route 2 across from a sign that reads “Welcome to Farmington,” was part of a major renovation and expansion project that was completed in May. The nonprofit agency serves adults with developmental and cognitive disabilities and employs 200 people throughout the county.

It is unclear who installed the heating system there. CN Brown, the company that owned and filled the propane tanks, did not respond to a call and email Friday but has previously declined to comment.

Propane, which is highly flammable, is odorless, but a chemical is added to give it a scent so that leaks can be detected. Firefighters follow safeguards when dealing with propane, including taking steps to ensure that nothing causes a spark that might trigger an explosion.

Investigators have not said how they think Monday’s explosion happened, but the blast blew the building’s walls off the foundation. Town officials have said this week that the foundation appeared to act as a chimney, sending the explosion up rather than out.

Even so, the explosion destroyed 8 of the 11 mobile home units behind the building.

Larry Lord, the 60-year-old maintenance manager who evacuated the building, was flown to Massachusetts General Hospital in Boston and is expected to be there for four months. He suffered burns over two-thirds of his body. His condition was upgraded Friday from critical to serious.

Five firefighters were taken Maine Medical Center after the blast, and three remained there Friday: Chief Terry Bell, 62, and Capt. Scott Baxter, 37, who are still in critical condition, and Theodore Baxter, 64, whose condition was upgraded Friday from serious to fair. Joseph Hastings, 24, was released from the hospital on Wednesday. Capt. Timothy “TD” Hardy, 40, went home on Thursday.

After state fire investigators left Thursday, a team of insurance investigators immediately took over and put up their own tape around the rubble, McCausland said.

Landry, who also is an insurance agent, said he expected the property and personal injury claims related to the explosion to be in the millions of dollars.

Morning Sentinel Staff Writer Taylor Abbott contributed to this report.