that this is because halon is highly toxic; in fact, it is because it can cause giddiness and mildly impaired perception, and due to the risk of combustion byproducts.) Flooding systems may be manually operated or automatically triggered by a VESDA or other automatic detection system. In the latter case, a warning siren and strobe lamp will first be activated for a few seconds to warn personnel to evacuate the area. The rapid discharge of halon and consequent rapid cooling fills the air with fog, and is accompanied by a loud, disorienting noise. Halon 1301 is also used in the F-16 fighter to prevent the fuel vapors in the fuel tanks from becoming explosive; when the aircraft enters an area with the possibility of attack, Halon 1301 is injected into the fuel tanks for one-time use. Due to ozone depletion, trifluoroiodomethane () is being considered as an alternative. Halon 1211 is typically used in hand-held extinguishers, in which a stream of liquid halon is directed at a smaller fire by a user. The stream evaporates under reduced pressure, producing strong local cooling, as well as a high concentration of halon in the immediate vicinity of the fire. In this mode, fire is extinguished by cooling and oxygen deprivation at the core of the fire, as well as radical quenching over a larger area. After fire suppression, the halon diffuses, leaving no residue. Chemical building blocks Chloromethane and bromomethane are used to introduce methyl groups in organic synthesis. Chlorodifluoromethane is the main precursor of tetrafluoroethylene, which is the monomeric precursor to Teflon. Safety Haloalkanes are diverse in their properties, making generalizations difficult. Few are acutely toxic, but many pose risks from prolonged exposure. Some problematic aspects include carcinogenicity (e.g., methyl iodide) and liver damage (e.g., carbon tetrachloride). Under certain combustion conditions, chloromethanes convert to phosgene, which is highly toxic. See also Halocarbon Haloalkane Halogenation References External links Gas conversion table Nomenclature FAQ History of Halon use by the US Navy Ozone Loss: The Chemical Culprits EIA Environmental Investigation Agency Environment Investigation Agency – EIA Global Environmental Investigation Agency in the USA Alphabetical list of all halomethanes Aerosol propellants DuPont Greenhouse gases Halogenated solvents Heating, ventilation, and air conditioning Refrigerants Fire suppression agents