EE & 2 EE'S WERE MOVING A 1500# 6'X8' SECTION F COARSE COAL SCREEN INTO POSITION. THE 6'X8' DECK WAS SUSPENDED BY 2 CHAINS. 1 AT EACH END OFTHE DECK & HOOKED IN THE CTR BY A CHAIN FALL HAN GING FROM A TROLLEY ON A 6"" I BEAM INJ WAS PUSHIG ON THE END OF THE DECK WHEN THE SOUTH END CHIAN SNAPPED THRU THE SAFETY CATCH ON THE CHAIN FALL ALLOWING THE END OF THE SCREEN DECKING TO FAL