EE HAD RECENTLY INSTALLED A RIB BOLT ON THE RIGHT SIDE OF #5 ENTRY WHEN THE EE LOWERED HIS CANOPY AND STARTED TO SWING THE RIGHT BOOM TOWARDS THE CENTER HOLE, A PIECE OF ROOF ROCK MEASURING 6' LONG X 2' WIDE X 0-2"" THICK, FELL FROM THE TOP,STRIKING THE EE IN THE LOW BACK.