Driller on LF-90 Core Drill was removing the bit from the core barrel. The driller put a 36"" pipe wrench on the bit and pulled on it. When the bit broke loose the pipe wrench slipped off. This caused the driller to fall with the pipe wrench in EE' hand. EE's thumb was pinched between the deck and pipe wrench on impact. The tip of thumb required 6 stitches to repair the damage.