EXCHANGE USED AN IMPACT GUN [APPROX. WT. 60-70#] FOR ABOUT 35 MIN. CAUSING VIBRATION AND FELT A SHARP PAIN TO LOWER LEFT BACK AND BOTH LEGS GAVE OUT CAUSING HIM TO STUMBLE BUT NOT FALL. EE C/O PAIN TO LOWER LEFT BACK RADIATING DOWN LEFT LEG, EE TAKEN OFF WORK BY HIS DOCTOR.