Picture a new residential tower going up in Mott Haven or along the Grand Concourse. You're a laborer carrying material across the sixth floor, moving fast because the pour is behind schedule. The plywood cover over the elevator hoistway — the vertical shaft where the elevator will eventually run — was pulled off that morning so the elevator subcontractor could take measurements, and nobody put it back. One step in the wrong place and you drop two stories into a concrete pit.