What started as a sprinkler water flow alarm (SWFA) on Friday night turned into a commercial fire in the 20100 block of 72 Ave. S., Kent, the Puget Sound Regional Fire Authority reported.

No one was in the building at the time of the fire and there were no injuries.

When firefighters got on scene they discovered that the entire warehouse and office spaces of the building were filled with smoke, Puget Sound Fire said. The engine company quickly upgraded the alarm to a full “commercial structure fire” to add additional units.

The fire appears to have originated where a forklift’s battery was being charged, fire officials said. The SWFA was set off when the heat from the fire activated the sprinkler head directly above it, exactly as it was designed to do, fire officials said. The movement of water through the pipes sent a signal to the alarm monitoring company, which called the local 911.

The activated sprinkler head controlled the fire and kept it from spreading, giving firefighters the time needed to access the inside of the building with fire hoses to fully extinguish it, Puget Sound Fire said.

Because of the size and height of the concrete tilt-up style building, firefighters are using large fans to clear out the smoke.

A fire investigator will go in once that is accomplished to confirm the cause of the fire.