PCB-containing transformer fires: decontamination guidelines based on health considerations

Realization that polychlorinated biphenyl-(PCB)-containing (askarel) transformer fires can produce toxic polychlorinated dibenzofuran (PCDF) and polychlorinated dibenzodioxin (PCDD) isomers has led to efforts to develop guidelines for cleanup of structures contaminated by soot from these fires. Two such fires have occurred in the United States in recent years, one in 1981 in Binghamton, N.Y., the other in 1983 in San Francisco. The phenomenon of PCB transformation to more toxic substances under conditions of uncontrolled combustion was studied in both locations, but much more extensively in New York. In terms of possible danger to human health, PCDFs comprise by far the most important PCB combustion products identified in the soot of both fires. PCDDs were not formed in sufficient quantity in either fire to constitute an important health hazard. The PCDF isomers of greatest health significance are the tetra-, penta-, and hexa- forms having all four lateral positions (2,3,7 and 8) chlorinated. Separate decontamination guidelines were established for each fire, based on different toxicity and exposure assumptions. One guideline was based on carcinogenic risk assessment of 2,3,7,8-TCDD and the other on experimental animal no-observed-effect level data for the same compound. More effort will be required to develop a generally accepted set of askarel fire decontamination guidelines.