THE EE WAS USING A PIPE WRENCH TO UNCOUPLE A SECTION OF 2""PIPE. WHEN THE WRENCH THAT HE WAS USING IN A PUSHING MOTION BROKE A NUT FREE IT RELIEVED ITSELF OF TENSION CAUSING AN OVER-EXTENSION OF THE WORKERS NORMAL STANCE, AT THIS TIME THE EE FELT A SENSATION OF PAIN IN HIS LOWER LEFT- HAND SIDE OF HIS BACK.