A sprinkler system inside the Planet Fitness at the Northwoods Mall stopped a small fire on Tuesday morning from potentially getting much worse.

Firefighters said they were dispatched to the gym around 7:20 a.m. for a fire alarm.

A caller said there was a fire in the electrical room, and the call was upgraded to a commercial structure fire.

First arriving units found light smoke and an activated sprinkler head in the electrical room.

Crews said the sprinkler extinguished the fire.

According to the department, the fire was likely caused by an electrical appliance failing, overheating and igniting.

There were no injuries reported.

The gym will be closed while the electrical equipment is replaced.