Investigators suspect an explosion in an apartment unit in northern Colorado Springs on Wednesday night was caused by a man attempting to make hash oil, police said.

The Colorado Springs Fire Department responded to a fire alarm at the 7700 block of Chanda Heights, just west of Academy and Briargate boulevards, about 10 p.m.

While nothing was ablaze when firefighters arrived, they found evidence of an explosion. The building’s sprinkler system had also been triggered, Colorado Springs police said.

The man was injured in the blast and was treated at the hospital for minor injuries.

According to police, the building sustained significant water damage, investigation into the explosion is ongoing and charges against the man have not been filed.

Wednesday’s explosion is at least the third linked to hash oil manufacturing in the city since December.