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LETTERKENNY, Pa. (CBS/AP) — Four people were injured, three of them seriously, in a small explosion Thursday in a vehicle shop at an Army depot, officials said.

The blast occurred at Letterkenny Army Depot in Chambersburg about 7:15 a.m., causing a small fire, said Col. Stephen Ledbetter, the depot commander.

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Army Depot officials quickly posted on social media the incident was contained, that operations elsewhere on the base would not be affected and that there was no suspicion of terrorist activity.

Ledbetter said three victims were flown to Baltimore-area hospitals with what he described as serious injuries. Their conditions were not immediately known.

Fire officials said they suffered burns. Ledbetter declined to discuss their injuries.

The fourth victim was treated at a local hospital and released. A hospital spokeswoman said the person had minor injuries, but no burns.

Ledbetter said the explosion occurred in the painting area of a vehicle shop where more than 300 people work. He said the building does not hold any munitions.

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Both the Army and the Occupational Safety and Health Administration will investigate, he said.

The depot, located 160 miles (257 kilometers) west of Philadelphia, or about 55 miles (88 kilometers) southwest of Harrisburg, employs about 3,600 people. The depot’s website says work there focuses on air defense tactical missile ground support equipment, mobile electric power generation equipment, Patriot missile recertification and route guidance vehicles.

(© Copyright 2018 CBS Broadcasting Inc. All Rights Reserved. The Associated Press contributed to this report.)