A hole was being drilled in the plant’s No. 8 Generator in order to remove a bore plug on a rotor undergoing maintenance. As workers were drilling the first hole, flames emanated from the drilled hole and injured a worker. A Ministry of Labour investigation found that the flames resulted from the release of hydrogen from pressurized containment inside the rotor core. The generator uses hydrogen gas as a cooling medium and a mixture of hydrogen and air was created as the compressed hydrogen escaped through the freshly-drilled hole. The mixture of hydrogen and air was within the flammable range for hydrogen and came into contact with mulitiple ignition sources capable of igniting the mixture, such as the motor of the drill or a work light. This resulted in the flames that emanated from the drilled hole. GE, the manufacturer of the generator, had prepared and made available a technical information letter which discussed the potential hazards associated with trapped hydrogen gas. It had recommended that the rotor core be tested and purged of hydrogen, not pressurized before plug removal, and the removal of potential sources of ignition. This information was not known to the team involved in the work, including the injured worker, and its recommended method was not followed. CLICK HERE for the Ministry of Labour – Ontario.ca Case File