2 MAINTENANCE PERSONNEL WERE LOWERING AND DRIFTING A FEED HOPPER TO THE FLOOR USING A CHAIN FALL AND LEVER CHAIN HOIST. AS THE HOPPER WAS BEING LOWERED THE CHAIN FALL SAFETY LATCH CAME LOOSE A ND THE HOPPER DROPPED SEVERAL FEET AND SWUNG AROUND, PINNING THE EE AGAINST ANOTHER PIECE OF EQUIPMENT. CONTRIBUTING FACTOR-IMPROPER RIGGING.