EMPLOYEE WAS CARRYING 2 PALLETS OF REFRACTORY BRICK ON FORKLIFT. FORKS WERE ELEVATED WHILE HE WAS BACKING UP WITH LOAD. FORKLIFT TILTED FORWARD DUE TO HEAVY LOAD CAUSING BRICKS TO SLIDE OFF FORKS AND EMPLOYEE WAS THROWN FROM INSIDE FORKLIFT CAB TO THE GROUND. EMPLOYEE WAS NOT WEARING SEATBELT INSIDE FORKLIFT.