KNOXVILLE, Tenn. (AP) _ A mailman is accused of trying to blow up his supervisor with a tank of propane.

Burl James McMahan Jr., 49, faces federal charges of assault, punishable by up to 25 years in prison, the Postal Inspector's Office said.

Police said McMahon placed the tank on his manager's desk Tuesday, opened the valve and tried to ignite the gas. The manager tried to throw the canister through a window, but the glass did not break. When the manager attempted to close the valve, McMahan tried to choke him, police said. A supervisor rushed in to help subdue McMahan until police arrived.

McMahan worked for the Postal Service for 11 years but had been on leave.

Postal spokeswoman Katrina Chalmers would not comment on a motive.