EMPLOYEE WAS CLEANING UNIT 1 #11 NORTH GRATE LAUNDER WHEN A PUFF OF HOT DUST CAME UP. THIS STARTLED HIM AND EVEN THOUGH HE HAD HIS PROPER PPE HE JUMPED BACK, STUMBLED BACKWARDS, CATCHING HIS FALL WITH HIS RIGHT ARM, STRAINING HIS SHOULDER. HE WAS EVALUATED BY A PHYSICIAN AND PHYSICAL THERAPY WAS STARTED ON 9-16-02.