A clear, corrosive liquid that has an extremely pungent odor and forms dense white vapor clouds if released. Both the liquid and the vapor 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. If it comes into contact with common metals, it will produce hydrogen fluoride, which poses a fire and explosion hazard. 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 this attack, and so the only significant stratospheric sink is eventual diffusion into the troposphere. [Chemical Week, v 164(45); 2002; 35] [Chemical Market Reporter, v 262(12); 2002; 31.] [Atmospheric Environment; 15; 1579-1582; 1981.] [Journal of Geophysical Research; 2; 443-444; 1975.]