PCBs are the common name for a class of chemicals known as polychlorinated biphenyls. They are man-made and do not occur naturally. Manufactured PCBs are typically oily liquids, either colorless or light-yellow in color, with no smell or taste.
First manufactured commercially in the United States in 1929, PCBs were found to have many uses due to heat resistant and fire retardant properties. They were used in a variety of products that include hydraulic fluid, pigments, carbonless copy paper, vacuum pumps, compressors, heat transfer systems, caulking, and in household appliances, such as refrigerators, television sets, and fluorescent lighting fixtures.
The primary use of PCBs, however, was as a dielectric fluid (a fluid that doesn’t conduct electricity) in electrical equipment. They were used in this fashion because of stability and resistance to thermal breakdown, as well as insulating properties. As a result, PCB oil was the fluid of choice for transformers and capacitors for many years; and, because of its fire resistance, it was actually required by some fire codes.