Abstract: Employees #1 and #2, of Columbia Gas, were dispatched to a residential site because, while the house was being checked for a sale, a plumber had discovered a leaking curb valve. Employees #1 and #2 were digging an area around the curb valve when the plumber left the site for 23 minutes. Upon his return, he heard a hissing sound. He checked the area where the two employees had been working and found that both had their faces down in the hole; one was bent over in the hole and the other was lying on his stomach, with his head hanging into the hole. Employees #1 and #2 were dead. They had been changing the curb valve without first turning off the gas.