Fire investigators say a fire at an apartment building in Bangor was intentionally set.

Bangor firefighters responded to the fire at a three-unit apartment building on Elm Street around 3:40 a.m. Thursday. Two people were inside and made it out of the building without any injuries.

Investigators with the State Fire Marshal’s Office responded to the scene and determined the fire was arson.

One firefighter suffered a minor burn injury.

The fire is under investigation.