GEISMAR - Authorities in Ascension Parish said four plant workers were injured, one of them severely, when a high-pressure hydrogen line exploded at a plant in Geismar overnight.

The explosion caused a fire at the Renewable Energy Group plant around 11 p.m. according to Ascension Parish Sheriff Jeff Wiley. He said three of the injured were contract workers, and the severely injured person was an REG employee.

Baton Rouge General said the four workers were brought to their burn unit, and one has already been discharged. They said one of the three still being treated is in critical condition.

Wiley said investigators believe the line was being worked on when it was pressurized with hydrogen, which caused a release. Something ignited the released hydrogen, which caused the explosion.

A shelter in place order was put out as a precaution while emergency crews fought the fire, and rail traffic through the area was also stopped.

Two people were injured earlier this year in a different fire at the Renewable Energy Facility.