Fire officials in Arizona are investigating an explosion that seriously injured one employee at Primex Plastics Corp. in Mesquite, Ariz.

The employee, whose name was not released by the Mesquite Fire and Rescue, was injured Wednesday morning as he was working on an electrical panel for one of the machines at the custom sheet extrusion company.

“They were working on an electrical panel, and when they fired it up, the panel arced. And when it arced, the explosive mixture with the dust in the air ignited, causing the explosion and then causing the fire to go up the wall,” Fire Chief Kash Christopher said.

“The occupants, God bless them, put the fire out with four extinguishers. So by the time we got there, the fire was already out,” he said.

It was about 5 minutes between the time the fire was called in and when firefighters arrived, Christopher said.

The Primex employee was transported by medical helicopter to University Medical Center in Las Vegas with burns on his face and upper torso, the fire chief said. “The injury was pretty serious.”

Operations at Primex were allowed to resume after the machine involved in the accident was shut down. Fire inspectors will return to Primex to inspect the machine before it returns to service, the chief said.