CASCO – A misfired shell during the Casco Days fireworks show set off an explosion on a barge in Pleasant Lake on Thursday night, injuring one worker.

State Fire Marshal’s Office investigator Rick Shepard said three employees, all men in their 20s, had started setting off the shells when one fired low.

“There were three shooters out on the barge,” he said. “The show had started, then there was a low-break shell,” one that doesn’t go up in the air all the way. “It ignited other shells, and at that point the shooters did the right thing and left the barge and dove into the water.”

One of the shooters, who was not identified, received burns and lacerations to his leg, said Shepard, who had been overseeing the set-up and show by Central Maine Pyrotechnics since Thursday afternoon.

“When the shells broke low and I saw people jump off into the water, I commandeered a boat and out we went,” he said. “They were back on the barge by the time we reached them.”

The injured man was treated at the scene.

Shepherd described all three men as “experienced” in their work.

He said the cause of the explosion is known but will not be released until the investigation is complete. He was taking statements late Thursday, he said, from the men.

Only one rack of five, 4-inch shells exploded.

The remaining five or six plus the finale were intact, and the men continued on and finished the show, he said.

Casco Days runs through Saturday and is sponsored by the Casco Firemen’s Association.