Gas From Nearby Nitroglycerin Blast Kills Worker in Manhole 3/4 Hour Later

A sewer worker was killed 45 minutes after nitroglycerin-based explosives were set off underground about 50 feet away, NIOSH has reported. Investigators from NIOSH, the National Institute for Occupational Safety and Health, said carbon monoxide gas from the blast 18 feet below ground caused a worker in a manhole to collapse. When two workers went in to rescue the victim, one got him out, but the other would-be rescuer collapsed in the manhole and died.

NIOSH said this death in August 1997 was the first known work-related death from this type of exposure to the gas. Carbon monoxide has no odor and can't be seen. The gas has been known to poison workers using gas-powered tools without enough fresh air (see Impact, May 1995). (Nitroglycerin was the main explosive, but not the only one.)

On the morning of August 4, a construction crew in southwest Atlanta set up a precast concrete manhole. At 3:45 p.m., workers for another contractor set off a blast to break up bedrock 6 feet below ground to lay pipe. At 4:30, a construction worker went 12 feet down to grout the manhole seams. He collapsed and two coworkers went in to rescue him.

Two days later, the city of Atlanta called in NIOSH to investigate. NIOSH measured carbon monoxide at 2,000 parts per million (PPM) in the manhole, coming through the soil. NIOSH says 1,200 PPM is "immediately dangerous to life and health." The MSDS (material safety data sheet) for the blasting materials didn't say carbon monoxide could be produced, said John Decker, of NIOSH.

The death shows that confined-space procedures must be used. During blasting, procedures are needed to protect people in nearby basements. And rescuers must be careful.

For more information, call NIOSH at 1-800-CDC-INFO (1-800-232-4636).