Abstract: At approximately 4:00 p.m. on November 21, 1988, Employees #1 and #2 were purging air from a 3/4 in. natural gas line that had just been pressure tested with air. They were waiting for the smell of mercaptar to signal the presence of gas, which would indicate that the air had been drained from the line. When they did not smell the mercaptar they turned off the gas line. Employee #2 had lit a match and was about to reopen the valve slightly to see if he could produce a flame when there was a bright flash and an explosion. Employees #1 and #2 were burned. Employee #3 was in the next room and was struck by flying debris. All three employees were hospitalized. Apparently, the room had been filling up with natural gas without their knowledge. Later tests confirmed that there was no mercaptar mixed with the gas.