The utility of PCBs is based largely on their chemical stability, including low flammability and high dielectric constant. In an electric arc, PCBs generate incombustible gases.
Use of PCBs is commonly divided into closed and open applications. Examples of closed applications include coolants and insulating fluids (transformer oil) for transformers and capacitors, such as those used in old fluorescent light ballasts, hydraulic fluids, lubricating and cutting oils, and the like. In contrast, the major open application of PCBs was in carbonless copy ("NCR") paper, which even presently results in paper contamination.
Other open applications were as plasticizers in paints and cements, stabilizing additives in flexible PVC coatings of electrical cables and electronic components, pesticide extenders, reactive flame retardants and sealants for caulking, adhesives, wood floor finishes, such as Fabulon and other products of Halowax in the U.S., de-dusting agents, waterproofing compounds, casting agents. It was also used as a plasticizer in paints and especially "coal tars" that were used widely to coat water tanks, bridges and other infrastructure pieces.
Modern sources include pigments, which may be used in inks for paper or plastic products. PCBs are also still found in old equipment like capacitors, ballasts, X-ray machine, and other e-waste.