Abstract: A traveling substation operator and a trainee stopped at a substation to perform a routine check of the station. On their arrival, they found a substation maintenance technician checking the air circuit breakers. The maintenance worker asked the substation operator to remove a spare air circuit breaker from a 5000-volt Westinghouse metal-clad switchgear cubicle so that it could be checked. When the 2.3- to 4.15-kilovolt, 600-ampere air circuit breaker (Model No. 50 H 150, manufactured in 1946) was removed from the cubicle, the employees discovered that the contact finger cluster was missing from the C phase bus bushing. The substation operator opened the shutter to check for the missing part inside the cubicle. When he tried to close the shutters, they jammed. He applied pressure to free the shutters, and an electrical fault occurred. The employees were burned by the ensuing electric arc, and they suffered from smoke inhalation. (The original abstract indicated that the burns were to the face, neck, chest, and legs, but did not indicate who was burned where.) The employees were hospitalized for their injuries.