EE WAS REMOVING BOLTS ALONG HF-6 CONVEYOR. HE WAS USING A PUNCH & A 3 LB HAMMER TO DRIVE OUT THE 3/4"" BOLTS THAT HOLD THE 20' SECTIONS TOGETHER. WHEN HE HIT THE PUNCH WITH THE HAMMER, HIS LEFT FOOT SLID DUE TO THE SNOW ON THE GROUND & HE FELT SOMETHING GIVE IN HIS LOWER BACK. HE CONTINUED TO WORK & HIS BACK GOT WORSE. THE SUPERVISOR WAS CALLED @ 10:20 AM AT WHICH TIME HE COMPLAINED