Substances and apparatus which , in the event of fire , may form dioxins 2.2.9.1.5 Substances and apparatus which , in the event of fire , may form dioxins include polychlorinated and polyhalogenated biphenyls ( PCBs ) and terphenyls ( PCTs ) and polyhalogenated biphenyls and terphenyls and mixtures containing these substances , as well as apparatus such as transformers , condensers and apparatus containing those substances or mixtures .