The power outage on Saturday morning caused the release valves on the 240,000-bpd DU-5 crude distillation unit (CDU) at the refinery to open, and static electricity set off a fire that was quickly extinguished, said people familiar with plant operations.

Shell gradually began resuming operations at the Norco refinery on Saturday, the sources said.

The power interruption took place on Saturday at an Entergy substation supplying the Norco refinery, Shell spokesperson Curtis Smith.

Norco is Shell's sole refinery in the United States. DU-5 is the only CDU at the Norco refinery.

No injuries were reported because of the fire, the sources said.

In a notice posted to area residents, Shell said power was restored to the refinery on Saturday afternoon.

CDUs do the initial breakdown of crude into feedstocks for all other units at a refinery.

(Reporting by Erwin Seba; Editing by Lisa Shumaker and Sherry Jacob-Phillips)

By Erwin Seba