Used primarily in industrial applications as a heat transfer fluid and dielectric fluid in electrical equipment such as transformers and capacitors due to its thermal stability and non-flammability. Also found use in hydraulic systems and as a plasticizer in polymers to improve flexibility and durability. Its persistence and resistance to degradation made it suitable for long-term applications, though environmental and toxicity concerns have led to restricted use. Historically present in some pesticide formulations as a synergist to enhance efficacy. Limited use today due to regulatory controls on chlorinated biphenyls.