One worker was missing and two were injured after an explosion sparked a fire at a Louisiana pipeline Thursday night, officials said.

Authorities don’t yet know what caused the fire on the Phillips 66 pipeline in Paradis, but a crew of six workers was cleaning it at the time, St. Charles Parish Sheriff Greg Champagne said at a news conference.

Two of the workers were hospitalized — one taken to a burn center— and three had minor or no injuries, the sheriff said. The remaining worker was unaccounted for, and a helicopter was being brought in to help search for him.