On June 22, 1982, the main power transformer at a private school in the midwestern United States became pressurized from internal arcing and vented approximately 50 gallons of askarel into the basement transformer vault. Areas of the building were contaminated. An oil sample contained 1.4 percent the polychlorinated-biphenyl (PCB) Aroclor-1260 (11096825), 33 percent trichlorobenzene (12002481), and 27 percent of a tetrachlorobenzene. Airborne PCB levels measured the day after the incident ranged from 50 to 90 microgram subic meter (microg/m3) inside the vault, 2 to 20microg/m3 in areas near the vault suspected of being contaminated, and below the limit of detection (0.24microg/m3) in other areas. The concentration distribution was similar for chlorinated benzenes. PCB surface concentrations ranged from a maximum of 5000 micrograms/100 square centimeters inside the vault to a minimum of 0.05 microgram/100 square centimeters in other areas. Neither polychlorinated dibenzofurans nor polychlorinated dibenzo-p-dioxins were detected. Based on questionnaire responses, individuals were stratified with respect to amount of exposure. Twenty five were classified as moderately exposed, and 33, who did not enter the building, were lightly exposed. Some moderately exposed persons reported headaches, unusual tiredness, skin irritation and redness, pimples, abdominal pain, nausea, dizziness, and numbness and tingling. Some lightly exposed persons reported headaches, nausea, pimples, itching, unusual tiredness, and increased eye discharge during the first week after exposure. There were no significant differences in symptom prevalence between the moderately and lightly exposed groups. While serum PCB levels were less than 5 parts per billion (ppb) in 37 percent of the cases, they ranged up to 16ppb in one individual. Except for a consistent and expected fasting elevation of triglycerides, no uniform deviation from normal was detected in blood testing. Significant differences were not detected in mean blood chemistry or hematologic values between exposure groups. Although there were several significant differences in blood chemistries and other clinical testing, these were minor and were not suggestive of any significant toxicity from exposure.