A four inch diameter drill casing used to load shot when blasting for bridge footings approximately 100 feet deep exploded. The employee was in a designated area assigned for loading the shot. The shot was complete and clean-up was being performed. Once the shot has been ignited in the casing, the casings are retrieved and placed into a scrap trailer. An employee was attempting to cut the casing with a cutting torch to fit into the scrap trailer when the casing exploded. The employee's face and arms were cut requiring stitches. He also has ringing in his left ear.