Electrical transformer fires can cause extensive smoke damage, especially when polychlorinated biphenyls (PCBs) are involved since they can form polychlorinated dibenzofurans (PCDFs) and other toxic by-products. To characterize the potential for by-product formation, this study was undertaken to optimize conditions for PCDF formation from PCBs and to study the potential for formation of PCDFs and polychlorinated dibenzodioxins (PCDDs) from combustion of selected dielectric fluids, including those contaminated with PCBs. A bench-scale thermal destruction system was used to combust the samples. The dielectric fluid was fed continuously using a syringe pump. The concentrations of CO, CO2, and O2 in the effluent were monitored continuously. The entire effluent from the thermal destruction system was passed through an XAD-2 trap to collect PCDFs and other semivolatile organics. The XAD-2 trap and a rinse of connective tubing were Soxhlet extracted. Extracts were cleaned using column chromatography to isolate the PCDFs and PCDDs. All samples were analyzed for PCDFs using HRGC/EIMS in the selected ion monitoring mode. The results of this work indicate that the optimum conditions for PCDF formation from PCBs are near 675C for 0.8 s or longer, with 8% excess oxygen. Under these conditions, percent levels of PCDFs are formed from mineral oil or silicone oil contaminated with PCBs at 5ppm or greater. PcDFs and PCDDs are also formed from a trichlorobenzene dielectric fluid which contained no detectable PCBs.

EPA 560/5-84-009 "Work Assignment no. 23. Interim Report no. 1. EPA Contract no. 68-02-3938. MRI Project no. 8201-A(23)." "November 19, 1984." "The work was done at Midwest Research Institute (MRI) during the period May 22, 1984 to November 19, 1984."