Abstract: At approximately 10:00 a.m. on August 16, 1999, Employees #1 and #2, were in a 5 ft by 5 ft by 2 1/2 ft deep excavation, repairing gas leaks in a PVC pipe system. They had already repaired four valves in the excavation. As they were working on a manifold, Employee #1 heard a hissing sound. The main shut-off valves were already closed, and the gas in the upstream lines were relieved. They returned to the excavation to bleed the residual gas. Employee #2 opened the valve and stood up to talk to Employee #1. A short while later, the gas ignited and flashed through the excavation. Employees #1 and #2 suffered first- and second-degree burns to their faces and hands. Both employees went to a nearby fire station and were taken to St. Francis Memorial Hospital in San Francisco.