EMPLOYEE WAS TRYING TO FREE UP TWO SECTIONS OF DRILL STEELS THAT WERE HUNG TOGETHER. HE WAS MOVING THE DRILL BOX IN AND OUT USING THE BOOM EXTENSION LEVER. HE MISSED THE EXTENSION LEVER AND HIT THE BOOM SWING. HIS HAND WAS ON THE DRILL STEEL AND WHEN HE HIT THE WRONG LEVER IT SWUNG THE CANOPY INTO HIS ARM, PINCING IT BETWEEN THE CANOPY AND DRILL STEEL.