EE WAS ADJUSTING COOLER PALLETS. THE PALLET ARM WAS HELD DOWN WITH 50TON HYDRAULIC PORTAPOWER HEAD. HE HAD JUST FINISHED TIGHTENING THE PALLETARM WHEEL BOLT & WAS REMOVING PNEUMATIC IMPACT W RENCH THE AIR HOSE TO THE WRENCH HIT THE PRESSURE RELEASE LEVER ON THE HYDRAULIC PUMP FOR THE PORTA POWER HAD & THE HEAD FELL OUT FROM THE TOP OF THE PALLET ARM & LANDED ON HIS TOES