Washington – The Chemical Safety Board recently announced plans to investigate the cause of the Aug. 6 fire at the Chevron oil refinery in Richmond, CA. No workers were killed, but CSB Chairman Rafael Moure-Eraso said the blaze ranks among the “most serious U.S. refinery incidents in recent years.”

The fire started when a combustible hydrocarbon liquid known as “gas-oil” leaked from a pipe attached to a crude oil distillation tower, according to a CSB press release. As workers tried to repair the pipe, the leak worsened and heat from the tower caused the gas-oil to form a large flammable vapor cloud.

CSB said workers were engulfed in the vapor cloud and could have been seriously injured if they had not escaped before it ignited.

The agency plans to examine why the pipe that failed had been kept in service during a maintenance turnaround in 2011, as well as industry practices for responding to this type of leak.