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MANASSAS, Va. (WUSA9) -- An investigation is underway to determine exactly what caused anexplosion late Monday morningin Manassas.

According to the Prince William County Fire Department, ahydrogen tank exploded in a buildingat 9441 Innovation Drive. The tank shot through the roof, and further damaged the building when it fell backdown.One employee suffered minor injuries.

The building, which houses the company UTRON,was evacuated. Several nearby offices were also evacuated as a precaution.

According to UTRON's website, itis "best known for its leadership in researching, designing, and building Combustion Light-Gas Guns for use as army artillery, naval guns, and direct-fire guns.
Past and present clients include the U.S. Navy, the U.S. Army, National Aeronautics and Space Administration (NASA), Ballistic Missile Defense Organization (BMDO), Department of Energy (DOE), National Science Foundation (NSF) and other organizations."

Sky 9 flew over the scene. It appears that the explosion, blew some windows out, knocked a door off, put a hole in the roof and blew some vents off of the roof. A Fire Department release states building inspectors have deemed the structure unsafe.