A small fire in the commercial building at 55 Post Road West was quickly extinguished Tuesday night before causing serious damage.

Firefighters were alerted to the fire just before 9 p.m. Tuesday when employees reported a burning odor had been detected in the structure.

Three engine companies with a total crew of six firefighters and one officer were dispatched to the scene.

At the building, two employees told firefighters they smelled something burning in a rear stairwell.

Firefighters discovered a small fire burning in a first-floor bathroom, which was doused. Smoke was then ventilated from the building using fans.

The cause of the fire, which was investigated by the Fire Marshal's Office, was a door that ignited while it was propped open against a wall-mounted heater.

All fire units cleared the scene shortly after 10 p.m.