Six workers were injured – four critically – by a fire last week at the ExxonMobil Refinery in Baton Rouge, Louisiana.

The U.S. Chemical Safety Board (CSB) says early indications are that the fire was ignited by flammable vapors that were released during unplanned maintenance around a pump. The CSB has sent a three person team to Baton Rouge to investigate the Nov. 22 incident.

The refinery one of 150 in the U.S. covered by OSHA’s Process Safety Management (PSM) regulations.

The CSB says a more comprehensive PSM system is needed in the U.S., in order to protect worker safety, public health, and the environment.  The modernization of process safety management regulations is one of the CSB’s Drivers of Critical Chemical Safety Change, a list of key chemical safety advocacy initiatives.