Banned PCB In Transformers Is Health Hazard
Many large electrical power transformers, used in underground substation vaults or commercial buildings, are insulated and cooled by special oils filling the steel tanks in which the transformers are enclosed. Because of the obvious fire hazard of petroleum derivatives, indoor transformers generally use a fire-resistant synthetic oil.
Until recently, when their further use was discontined, polychlorinated biphenyls or PCB compounds were common. PCBs were banned because of their long-term environmental contamination hazard, although they are not normally combustible.
However, fire fighters should now add PCBs to their list of problem chemicals because of an incident last December 9 in a downtown Toronto transformer vault. An electrical failure burned a hole in the tank of a PCB-cooled unit, allowing several gallons of the liquid to escape. Most of it was vaporized by the electrical arc itself.
Both fire fighters and utility workers were exposed to the decomposed fluid. Later, several workers showed symptoms of PCB poisoning-skin rashes, nausea, headaches, and eye irritation. The utility employees wore “protective equipment” of unspecified nature. A union official claimed, however, that the PCB material “goes right through” the gear used, which “soaks it up like a paper towel.”
Canadian utility officials had heard of no similar occurrences in the United States where hundreds of similar transformers are in use, but they did issue a list of fire fighting and general safety guidelines following this incident. Fire fighters are warned to wear full protective clothing and avoid skin contact with PCB liquids involved in electrical fires, even during overhauling operations. Since there is no quick way to tell the nature of transformer coolants in an emergency situation, this precaution should always be taken.
Further information on this situation should be available through the Toronto Fire Department.
Manufacture of PCB-cooled transformers has been stopped. However, many units remain in service.
