A fire and explosion at a Silver Spring apartment complex last Thursday has been ruled an accident by local and federal authorities investigating the incident, Montgomery County fire chief Scott Goldstein told media Monday afternoon.

Goldstein said investigators with the Montgomery County Fire and Rescue and from the federal Bureau of Alcohol, Tobacco, Firearms and Explosives have completed their on-site investigation of the explosion, sifting through debris outside and inside the remaining parts of the structure.

“Montgomery County agencies are working on plans to execute a transition tomorrow, turning the property back over to property management,” Goldstein said.

Investigators have concluded that the explosion, which rocked one of the buildings in the Friendly Gardens Apartment complex, came while maintenance workers were attempting to fix a clogged drain in one of the units. One of the workers, Goldstein said, accidentally cut a gas pipeline in the building’s basement, and then went back upstairs to the apartment where the clog had been reported.

The worker and the apartment resident were in the unit when a sudden fire caught in the unit – which Goldstein referred to as a “flash thermal event” — injuring the resident and causing the resident and the worker to begin to evacuate the building using the back stairwell. The explosion took place while they were in the stairwell.

County Executive Marc Elrich thanked Montgomery County Fire and Rescue personnel for their quick response to the scene. He also said there could be two directions for policy-making to prevent such an event from happening again: first and foremost, ensuring that gas pipes are appropriately labeled, and secondarily ensuring that maintenance personnel receive adequate training or walkthroughs so that they are aware of gas pipes and other hazards while on the job.

“It wasn’t a black gas pipe,” Elrich told media on Monday afternoon. “It was indistinguishable from the other pipes in there.”

14 people were initially hospitalized after the explosion. As of Monday afternoon, Goldstein said 12 had been discharged. One is still in critical condition, and the other is receiving care for a medical condition not connected to the explosion.

Last week, dog search units indicated the possibility that someone could still be trapped in the building debris. However, Goldstein said that after continuing the search with K9 units throughout Friday and Saturday, investigators are confident there are no fatalities. “There’s no concern of a person who was in the wrong place at the wrong time,” Goldstein said. “So that is very good news.”

Some residents in other buildings in the complex have been allowed to return to their homes, but close to a hundred remain displaced. In the aftermath of the blast, the county’s health and human services department set up crisis receiving centers at the Gwendolyn E. Coffield Community Recreation Center and White Oak Recreation Center. Residents of the building that exploded will be allowed to return on Tuesday to units that are still accessible, Goldstein said, to collect essential items.

Patrick Campbell, with the Montgomery County Department of Health and Human Services, said all residents will get some financial assistance, even those who were only temporarily displaced, and the first payments will go out on Tuesday.

Working with Montgomery Housing Partnership, the county has raised more than $460,000 to help house residents displaced by the disaster. Disbursements from the fund will start Tuesday and Wednesday, Campbell said.

DHHS has identified 41 families, including 124 adults and 36 children, in the buildings primarily impacted by the explosion.

“We’re trying to make sure that we bring every type of service they could possibly need,” Campbell said.