EE was taking off a belt guard on the impactor to correct the belt. Standing on the bottom conveyor of the PEP plant, he stepped on some frost, slipped and fell, landing on his back. He had difficulty breathing and was taken by amulance to the E.R. at St. Anthony hosp. where it was determined that he had a bad bruise. Released by 200 p. He was his own dr. was ok to return to work