Tesoro said its refinery in Campbell Industrial Park vented and burned 1,200 pounds of sulfur dioxide Monday because of an unexpected shutdown of the plant’s sulfur recovery unit.

The unit was shut down for 20 minutes and the event had no impact on the operations at the plant that has a refining capacity of 93,500 barrels a day, Tesoro said.

“Per design, excess hydrocarbons were vented and burned off in the refinery’s flare,” according to an email from the company.

The event was reported to the National Response Center because the sulfur dioxide released was in excess of reportable limits, according to the company. U.S. refineries must notify the response center if they release hazardous substances in excess of reportable quantities, according to the Comprehensive Environmental Response, Compensation and Liability Act, commonly known as Superfund.