WEST JEFFERSON, Ohio - An explosives experiment blew up Sunday afternoon inside a lab at the world's largest independent, nonprofit research institute, critically injuring two researchers with burns and shrapnel wounds, a spokeswoman said.

        Jim Gombarcik, 30, of Delaware, and Tom Burky, 34, of Johnstown, were combining “energetic materials” in a device that resembles a cement mixer when the explosion occurred at a Battelle Memorial Institute lab, spokeswoman Katy Delaney said.

        “These are very experienced guys with this sort of thing, and we do this type of research all of the time,” she said.

        Mr. Gombarcik was flown by helicopter to Ohio State Medical Center, where he was in surgery in critical condition Sunday night. Hospital spokesman Ken Philips said his left arm was badly injured and he was burned over a third of his body. Mr. Burky was in critical condition at Grant Medical Center

        The men work for a Battelle division that researches security technology, munitions and explosives, Ms. Delaney said. She did not know what type of substances they were mixing.

        The explosion happened inside a sealed “blast chamber,” a room that can withstand such an explosion, she said.

        The institute, headquartered in Columbus, has had a hand in the Manhattan Project, which developed the atomic bomb, and government contracts represent almost 90 percent of its revenue.

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