Fire investigators worked through the night to determine what caused an explosion at an apartment complex Monday afternoon.

The 4:48 p.m. explosion occurred in the laundry room of an apartment building at 825 E. 600 South.Salt Lake Fire Battalion Chief Bruce McGill said the blast may have been caused when someone used gasoline in a washing machine, which was ignited by the water heater's pilot light. "It's all speculation at this point, but we will investigate," McGill said.

Another fire official, who didn't want to be identified, said it appears someone was trying to remove tar from clothing with the gasoline. "Gasoline gets grease out of greasy clothes, but this is the ultimate," he said.

The explosion is estimated to have caused $15,000 to $20,000 in structural damages, McGill said.

Lorinda Bailey, 25, who lives in an adjacent apartment with her two small sons, said, "It made my ears ring. It (the explosion) rocked the apartment."

The blast left an 8-foot wide and 4-foot long hole in Bailey's apartment. The explosion sent concrete blocks and other debris cascading into Bailey's apartment, where her 2-year-old son was playing. He was uninjured.

McGill said residents in one apartment were evacuated when the wall collapsed. Other residents may be evacuated after the damage is assessed. He said the blast's force ripped out steel support and other concrete reinforcement of the building's bearing wall.

Fire officials said they turned off gas meters for the evening to avoid other possible fire hazards.