(Reuters) - A power outage at a Valero Energy Corp refinery and resulting smoke on Friday forced residents to remain indoors for several hours in the San Francisco Bay city of Benicia, California.

The dense, black smoke from the Benicia refinery, as it flared off hydrocarbons it could not process normally, also caused traffic to back up on Interstate 680 and forced evacuations from the industrial park where Valero’s plant is located, according to local news media reports.

By noon PDT (1900 GMT) orders to remain indoors and evacuate the industrial park had been lifted, according to the Benicia Fire Department

Valero said the 145,500 barrel-per-day refinery lost its power supply at about 6:45 a.m. PDT from Pacific Gas & Electric on Friday, forcing it to use the flare system.

Energy industry intelligence service Genscape said all monitored units at the refinery were shut down on Friday following the power outage.

Power was restored to the refinery within a few hours.

Two people were treated for respiratory distress, the fire department said.