Abstract: A sole owner (without employees) of a contracting firm was performing maintenance and repair work for a cork processing company. He was working on the motor for a Nu Vac 480-volt, 14.9-kilowatt pneumatic roof-mounted conveyor system. He found the motor to be running roughly. As he was examining it, the motor tripped the electric starter. He went to the electrical room on the third floor of the building to open the Square D 60-ampere, standard-duty disconnect switch rated at 600 volts. An explosion and electrical fault occurred, involving not only the switch but also a portion of the surrounding electric equipment. The ensuing electric arc burned the contractor. He was hospitalized with first- and second-degree burns to his right hand and arm and his face. The company processed cork, including grinding, sifting, and blending cork. Because of inadequate housekeeping, combustible cork dust was present throughout the electrical room. The open-type electric equipment was unsuitable for use in Class II, Division 1 or 2 locations.