MINNEAPOLIS (WCCO) – The cause of a south Minneapolis business fire, which blew up multiple propane tanks last week, is unknown based upon the evidence, authorities said.

The Smith Foundry, located at 1855 East 28th St., caught fire around 9 p.m. Friday, according to the Minneapolis Fire Department. Crews responded shortly after and found flames sprouting from a storage building. Firefighters found stacks of wood pallets on fire, but they also noticed that the flames were creeping toward a rack of propane cylinders.

The heat caused several of the cylinders to explode, the department said. The explosions intensified the fire.

Crews attacked the fire from the outside and extinguished the majority of it before focusing on the flames inside the building. Only the storage building sustained fire damage, the department said.

One firefighter suffered from heat exhaustion. An ambulance took him to the Hennepin County Medical Center, where he was treated and released that night.

The fire was under control shortly before 11 p.m., the department said.