An explosion and fire heavily damaged a downtown Lake Oswego restaurant late Saturday.

No one was injured at the incident at Scratch Restaurant, 149 A Ave. Fire investigators believe a faulty ceiling fan may have contributed to the blaze, but they were unable to determine a cause of the fire with any certainty.

Damage was estimated at about $50,000.

Lake Oswego firefighters responded to a report of an explosion and fire at the restaurant at 11:33 p.m. on July 19. They arrived to find the front windows blown into the street, smoke coming from the building, and a fire was burning in a room off of the main restaurant area.

Battalion Chief David Morris said it’s possible that the window damage was caused by a smoke explosion. “A smoke explosion occurs when the products found in smoke mix with air, creating a flammable mixture,” he said. “When this flammable mixture finds an ignition source, it creates an explosion, similar to what happens when a cloud of gas reaches an ignition source.”

Firefighters advanced hose lines into the structure and were able to bring the fire under control in less than 10 minutes. There was no evidence that anything in the kitchen itself was involved in either the fire or subsequent explosion, investigators said.

Additional firefighters checked neighboring occupancies to ensure the fire had not spread to those tenant spaces.

It was determined that the fire was contained to the original occupancy. No one was in the business when the explosion occurred and no injuries were reported.

Lake Oswego firefighters were assisted by Tualatin Valley Fire and Rescue at the fire and Portland Fire & Rescue provided an engine to help cover other 911 calls.