Fire extinguishers contain different chemicals, depending on the application.
By international agreement , however, production of all types of halons ceased in 1994 because the bromine and chlorine atoms in the chemical were found to migrate over time to the stratosphere, where they react to deplete ozone in a very efficient catalytic cycle. Many fire extinguishing systems are built into the building or other structure being protected. Water sprinklers are by far the most common type of fixed system because they are inexpensive, highly reliable and safe for people. CO 2 works well, but is fatal at the concentrations necessary to extinguish a fire, and so cannot be used where people will be present. The phaseout of halons has led to a scramble by government and industry researchers to find environmentally suitable replacements .