Ee#1 & ee#2 were removing 90lb half moon shaped eccentric cover in preparation for new piece of installation. as the 2 ee's proceeded ee#1 was backing up to ascend a step & his pant leg got caughton the metal step & he fell backwards. Ee#2 (the injured ee) received the complete load & threw it to the side so it wouldn't hit ee#1. As ee#2 did this he pulled his back.