Abstract: On January 27, 2005, four employees, all mechanics, were repairing and replacing leaky valves on a hydrogen-gas compressor. Initial repairs were conducted and the system was tested for leaks. One of the valves still had a leak due to a burr inside the compressor, which did not allow the valve to seat correctly. Without locking out the system, the employees attempted to use a grinder to remove the burr. A flash fire occurred and all four employees were injured. Three of the employees received first and second degree burns on their face, arms, and legs, requiring hospitalization. The fourth employee suffered minor injuries to his eyes and experienced hearing loss, but was not hospitalized.