INJURED EE WAS BEING SHOWN ACCESS TO THE TOP OF COAL BINS AS PART OF HIS TRAINING. AS THEY DESCENDED A SHORT STAIRWAY TO THE TOP OF BIN, EE WAS IN THE LEAD. HE OVERSTEPPED A STAIR AND PART OF HIS HEEL LANDED ON THE STAIR. AS HE LIFTED HIS OTHER FOOT HIS WEIGHT SHIFTED TO THE UNSUPPORTED FOOT AND IT SLIPPED OFF THE STAIR. HE GRABBED HANDRAIL AND JERKED HIS ARM BACKWARD.