A municipal sewer project involved the installation of new pipes and manholes. Explosive blasts were used to break up rock layers 6 feet below the surface before excavating pipeline trenches and manhole pits. On the day of the fatality, a construction crew installed a 12-foot-deep manhole without incident. After the crew left the area, 265 pounds of nitroglycerin-based explosive in 20 boreholes, each 18 feet deep, were detonated 40-60 feet from the manhole. A worker who entered the manhole 45 minutes after the explosion collapsed within minutes, and two coworkers descended into the manhole to rescue him. One rescuer retrieved the unconscious worker before collapsing on the surface, and the other rescuer died in the manhole. All involved construction workers had elevated blood levels of carboxyhemoglobin indicating they had inhaled air containing high CO concentrations.