EE WAS ASSISTING SETTING CRIBBING UNDER A DRAGLINE PINION THAT WAS GOING TO BE WORKED ON IN THE WELDING SHOP. AFTER SETTING CRIBBING MATERIALS EE TOOK A STEP BACKWARDS & PLACED FOOT ON A HOIS T LINK LOST HIS BALANCE & FELL BACKWARDS ONTO THE SHOP FLOOR. EE'S LOWER BACK AREA LANDED UPON A CLEVIS THAT WAS LAYING ON THE FLOOR IN THE WORK AREA. EE CONT TO WORK THAT AM & REQUESTED PM