A small explosion and fire in the paint area of a production facility at a Pennsylvania Army depot injured four workers — three seriously — on Wednesday morning, according to the depot commander.

"We do not suspect any type of terrorist activity," Col. Stephen Ledbetter said at a news conference, adding that the investigation into the cause of the explosion is ongoing.

Three of the four victims were airlifted to Baltimore area hospitals from the Letterkenny Army Depot, located near the Maryland border.

The Franklin Fire Company said an unspecified number of victims suffered burns.

Ledbetter said he did not know if they faced life-threatening injuries from the blast and fire around 7:20 a.m., but added "since three of the four were medevaced, yes, I would classify them as serious."

The fourth victim was treated and released from the hospital by Wednesday afternoon, WGAL News 8 reports.

Ledbetter said the facility where the explosion occurred does not handle munitions, rather vehicles and other "large pieces of equipment."

The Letterkenny Army Depot, a sprawling 18,000 acre facility in Chambersburg, Pa., is used to maintain and manufacture equipment for tactical missile air defense systems. The depot operates under the U.S. Army Aviation and Missile Command.

"Letterkenny has an exemplary safety record," Rep. Bill Shuster, R-Pa., a congressman whose district covers Chambersburg, said in a statement, "and I'm confident a thorough investigation will be conducted to determine the cause of this incident and how it can be prevented in the future."

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