RICHMOND -- A half-acre brush fire that damaged school outbuildings and injured a bystander and two firefighters in Contra Costa County is being treated as suspicious, investigators said Monday.

Crews were dispatched about 3 p.m. on Sunday to 3800 Clark Road near East Bay Waldorf School for a report of a vegetation fire, according to Contra Costa Fire Battalion Chief Lon Goetsch.

Firefighters found the blaze burning on a steep hillside close to Wildcat Canyon Park. The fire involved heavy brush and threatened two outbuildings and a residential structure on the school's campus.

They also found a man attempting to extinguish the fire, Goetsch said. The man, whose name was not released, suffered minor smoke inhalation and was transported to Doctors Medical Center in San Pablo, where he was treated and released.

More than 50 firefighters from El Sobrante, Richmond, San Pablo, Pinole, El Cerrito, East Bay Regional Parks Fire spent three hours battling the blaze, which eventually was contained to about half an acre.

A few outdoor buildings used to store school gardening equipment were scorched, Goetsch said, and two firefighters who responded to the blaze suffered minor injuries after being stung by bees.

No one was seriously injured.

It was not immediately known what caused the fire but the blaze appeared to be suspicious in nature and remained under investigation on Monday, Goetsch said.

Anyone with information about the blaze is asked to call 1-866-502-7766 or 1-866-50-(ARSON).

Contact Natalie Neysa Alund at 510-293-2469. Follow her at Twitter.com/nataliealund.