A CCl4 fire extinguisher would have to contain a non-flammable and non-oxidizing gaseous propellant, besides the CCl4, under high pressure. The most
likely gaseous propellant would be N2, but a mixture with CO2 would be quite possible. However, becauise of its alleged liver toxicity, CCl4 for fire
extinguishers have been replaced by BCF ones, containing liquid pressurized bromochlorodifluoromethane (Halon 1211 or BCF), CF2ClBr, which is
substantially more expensive, and which vaporizes on release at atmospheric pressure unlike CCl4. But even this, being a volatile chlorobromocarbon,
is now out of favor because of its ozone-layer damaging property. CO2 fire extinguishers are usually used instead, although having a lower normal
boiling or sublimation point it has to be kept in heavier vessels under greater pressure. Another good possible substitute would be CF4.
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