EMPLOYEE WASLIFTING BOXES OF ACID OFF A PALLET ONTO A TABLE IN THE LAB. HE HAD LIFTED 3 BOXES OF ACID WEIGHING 40# AND THEN LIFTED A BOX OF PHOSPHORIC WEIGHING 57#, THE UNEXPECTED DIFFERENCE CAUSED HIM TO JERK FORWARD. WAS EVALUATED BY A PHYSICIAN ND PHYSICAL THERAPY STARTED ON 7-18-00.DIAGNOSIS OF BACK STRAIN.