HF, A clear, corrosive liquid that has an extremely pungent odour and forms dense white vapour clouds if released. Both the liquid and the vapour can cause severe burns to all parts of the body, and medical treatment is required for all exposures. In fact, HF burns covering only 2% of the body can be fatal. If this chemical comes in contact with glass, concrete and other silicon-containing materials, it yields silicon tetrafluoride gas. In general, this chemical is used to produce environmentally safer fluorocarbon products, chemical derivatives, and fluoropolymers. Environmentally speaking, hydrofluoric acid is much too reactive to ever reach the upper atmosphere, and tropospheric sources therefore do not interfere with the ozone layer. Hydrogen fluoride, however, is produced in situ in the stratosphere by the photolytic destruction of anthropogenic CFCs. And while this process also frees atomic chlorine which catalytically destroys ozone, Cl can be sequestered as HCl, and temporarily removed from the O₃ destruction cycle. Analogously HF also forms but unlike the chlorine reservoir species HCl which is eventually broken apart by hydroxyl radical, HF is too stable for th OH dot attack, and so the only significant stratospheric sink is eventual diffusion into the troposphere.