An enclosed space accident that resulted in two fatalities occurred while a three man crew was attempting to shut down a 24 inch water main in a 10 foot deep valve pit as a result of a break in the water line. The workers were employed by the water distribution division of the city water and sewer department. The crew had hit and ruptured a 24 inch water line while boring under a street; the crew was then instructed to close valves at three locations. At one location, a worker entered the pit through the 22 inch manhole opening and a few minutes later called for help. A second worker entered the pit to assist and was overcome. A third worker started in but realized that he would be in trouble. He exited immediately to get help. The fire department and rescue squad arrived on the scene and started rescue procedures. Four 30 minute cylinders were discharged into the space in an attempt to improve the atmosphere. Both workmen were removed from the pit and transported to a local hospital where they died a short time later. After the workmen were removed from the pit, the fire department tested the atmosphere and found 17 to 18 percent oxygen. No hydrogen-sulfide, methane, or carbon-monoxide was detected. The cause of death for both workers was considered to be asphyxiation resulting from oxygen deficiency. A valve pit downstream from where the accident occurred contained 3.0 percent oxygen. The author notes that the victims were preoccupied with shutting down the valve and failed to test the atmosphere before entering the pit and did not follow safe work practices. Employers should provide specific information about hazards in their employee safety manuals, especially when tasks to be performed are life threatening.