A Wednesday morning explosion at the Exxon Mobil Corp. refinery in Torrance injured four workers and pushed up the local price of wholesale gasoline. The workers suffered only minor injuries, according to an Exxon spokesperson.

The South Coast Air Quality Management District issued an air advisory, asking anyone who can see or smell smoke caused by the explosion to avoid outdoor exposure.

“Emergency procedures have been activated to address the incident,” an Exxon spokesman said in a statement.

The 8:50 a.m. explosion started a fire that was quickly extinguished by firefighters. But footage and photos from television news crews and local residents who posted to social media showed huge flames much larger than what typically shoots from the refinery's flare stacks. The Torrance Fire Department said that those flames were part of a flare system that had activated as a safety feature – one that people would see while driving by.

Los Angeles wholesale gas on Wednesday traded at a 12 cent premium to the same fuel in San Francisco, the largest spread since Jan. 27.

Roughly 650 employees and 550 contractors work at the refinery, a 750-acre facility bounded by 190th Street, Crenshaw Boulevard, Del Amo Boulevard and Prairie. The refinery processes an average of 155,000 barrels of crude oil per day and produces 1.8 million gallons of gasoline each year. It is the sixth-largest refinery in California, and the third largest in the L.A. area.