SUBCONTRACTOR LANDED ON CONCRETE GRADE WHEN HE STEPPED THROUGH THE 42"" SQUARE OPENING IN THE PLATFORM HE WAS PREPARING TO COVER. HE LANDED ON HIS BACK AND SHOULDER. HE SUFFERED A BROKEN COLLARBONE, 2 BROKEN RIBS, AND A CONCUSSION. PLATFORM HAS BEEN BARRICADED WITH CAUTION TAPE UNTIL WORK COMMENCES.