OSHA Hazard Information Bulletins
Work Practices Employed by the Electric Utilities Industry Regarding Sulphur
Hexaflouride Gas-Insulated Circuit Breakers

January 30, 1989

An inquiry was forwarded to this office by the OSHA New York Regional Office regarding a possible safety hazard associated with sulphur hexaflouride (SF(6)) circuit breakers used by electric utilities in high-voltage transmission and distribution applications. The Edison Electric Institute (EEI) was most helpful in providing information necessary for this bulletin.

In response to the above inquiry, we conducted a series of investigations including discussions with utility industry representatives and an on-site visit to a utility substation to determine any potential existing hazards. According to the EEI, member companies have been using SF(6) gas-insulated circuit breakers for 20 years with associated maintenance hazards being well-known within the industry. The chief safety hazard is the potential exposure of maintenance employees to residual toxic by-products of SF(6) breakdowns that occur after the gas is exposed to a series of arcings. In most cases, the by-products (when present) may total a few grams. EEI estimates that SF(6) equipment is used in general about 80 percent outdoors and above ground, 15 percent indoors and 5 percent below ground. Attached is one company's substation maintenance bulletin containing work practices for SF(6) gas-insulated equipment.

During the on-site local substation visit, Virginia Power Company personnel demonstrated maintenance procedures for a 230 kilovolt Westinghouse circuit breaker which was undergoing door seal replacement due to a leak. The observed Westinghouse unit consists of three interrupters and housings sharing a common gas system. (See attached photograph.) Low pressure, 45 psig SF(6) surrounds the interrupter and acts as an insulator. High pressure (approximately 270 psi) SF(6) is used to extinguish arcing during an interruption cycle. After the gas was evacuated from the breakers and deposited in a gas reclaiming system, and prior to replacing the door seals, Virginia Power personnel demonstrated what they would do if the presence of SF(6) by-products had been found. The Virginia Power personnel wore protective clothing with air purifying respirators and used vacuum cleaners with high-efficiency particulate air (HEPA) filters to demonstrate the manner in which toxic residue would be removed if it were present.

Also attached is a response prepared by EEI to OSHA questions regarding SF(6) equipment. The attachment provides, among other things, information on the design and potential failure of equipment and detection of gas leaks. It also addresses precautions that must be taken if equipment is located in a confined space.

Please distribute this bulletin to Area Offices, State Plan States and Consultation Projects.