A confined space accident resulting in two fatalities, which occurred when a self employed contractor was performing an inspection of a backflow device in a city water line that ran underground along the front of a sawmill, was described. The contractor and a shipping supervisor from the sawmill who attempted to rescue him died; a maintenance man, two policemen, and two paramedics were overcome while attempting a rescue. The backflow device being inspected was located in a 12 by 6 by 8 foot underground vault accessible through a 30 inch manhole at the surface. The contractor used a ladder to enter the vault; about 30 minutes later, his body was seen in the water at the bottom of the vault. The shipping supervisor and the maintenance man entered the vault in a rescue attempt, but both collapsed within minutes. Two policemen and two paramedics entered the vault, but had to be helped out. Firemen wearing breathing apparatus were finally able to enter the vault and remove the three men. The contractor and the supervisor died as a result of asphyxiation and drowning. The maintenance worker was hospitalized in serious condition and the two policemen and paramedics were treated and released. The atmosphere in the vault was found to contain 7 percent oxygen (7782447) and 3 percent carbon-dioxide (124389). No hydrogen-sulfide or explosive gases were detected. Carbon-dioxide and wastes generated by bacterial action and algae growth apparently had displaced the oxygen in the atmosphere. The self employed contractor was a one man operation with no safety program or confined space entry procedures. The authors recommend implementing a safety program for contracted services, especially if they involve hazardous operations such as entering confined spaces, and training of emergency response personnel in confined space hazards and rescue procedures.