Investigators say a maintenance worker inadvertently caused an explosion in a residential building in Silver Spring on Thursday.

The worker accidentally cut through a gas line while attempting to fix a plumbing issue, the Washington Post reported. Officials with Montgomery County Fire are still uncertain what ignited the explosion, but said it could have come from a number of different commonplace sources.

Despite Montgomery County Executive Marc Elrich telling reporters that the Friendly Garden Apartments complex was up to date on its inspections, records indicate the building that exploded Thursday was years behind on its fire permitting.

The residential building at 2405 Lyttonsville Road in Silver Spring had a Fire Code Compliance Permit that expired in 2019, Fox 5 reported.

The explosion injured more than a dozen people, according to authorities, and led to substantial collapse of the building due to the ensuing fire. According to records, Friends Non Profit Housing owns the building, which is registered at the same address as ResidentialONE Property Management.

Residential buildings in Montgomery County must receive an inspection at least every three years, part of a law passed after a 2016 explosion at the Flower Branch apartments that killed seven people, not far from the Friendly Garden building.

That inspection is meant to include common areas and private units, but the Friendly Garden Apartments complex had only received an inspection of its common areas as of September 2021. An inspection of the residential units had been delayed due to Covid-19 and a change in management, a spokesperson for Elrich's office told Fox 5.

Roughly half of the 200 residents of the Friendly Garden Apartments complex have been allowed to return to their homes as of Saturday.

UPDATE, MARCH 7, 5:30 P.M. ET: This story has been updated to include information about the cause of the explosion.