While emptying a PEX sack a chunk of PEX was binded up, the operator went up on the grading deck & tried to loosen the bind with a crowbar. He pushed the sack to get the chunk of PEX out, and leaned against the safety chain when the chain came unhooked. He fell on the hopper spike, which is used for cutting the bottom of the sacks. He received a laceration to the chest area.