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VENTURA, California (AP) -- A teacher who kept a 40 mm shell on his desk as a paperweight blew off part of his hand when he apparently used the object to try to squash a bug, authorities say.

The 5-inch-long shell exploded Monday while Robert Colla was teaching 20 to 25 students at an adult education class.

Part of Colla's right hand was severed and he suffered severe burns and minor shrapnel wounds to his forearms and torso, fire Capt. Tom Weinell said. No one else was injured. He was reported in stable condition at a hospital.

The teacher slammed the shell down in an attempt to kill something that was buzzing or crawling across the desk, said Fire Marshal Glen Albright.

Colla found the 40 mm round while hunting years ago and "obviously he didn't think the round was live," said Dennis Huston, who teaches computer design alongside Colla.