INJURED WAS INSTALLING 24' BOLTS. AT THE END OF DRILLING THE 24' HOLE WHILE HOLDING THE DRILL STEEL TO THE ROOF, HE WENT TO GRAB PIPE WRENCH WHICH WAS ON STEELS. AS HE DID, HE INADVERTENTLY HIT ROTATION LEVER AND PIPE WRENCH SPUN ON STEELHITTING BACK OF RIGHT HAND, CAUSINAG CONTUSION.