Fire extinguisher had been developed by DuPont and the US Army in 1954. Both 1211 and 1301 work by inhibiting the chain reaction of the fire, and in the case of Halon 1211, cooling class A fuels as well. Halon is still in use today but is falling out of favor for many uses due to its environmental impact. Europe and Australia have severely restricted its use, since the Montreal Protocol of 1987. Less severe restrictions have been implemented in the United States, the Middle East, and Asia. Internationally there are several accepted classification methods for hand-held fire extinguisher. Each classification is
Fire extinguisher are dissolved in water, whereas the agents used in condensed aerosols are microscopic solids. In 2015, researchers from George Mason University announced that high volume sound with low bass frequencies in the 30 to 60 hertz range drives oxygen away from the combustion surface, extinguishing the fire, a principle was previously tested by the Defense Advanced Research Projects Agency (DARPA). One proposed application is to extinguish fires in outer space, with none of the clean-up required for mass-based systems. Most countries in the world require regular fire extinguisher maintenance by a competent person to operate safely and effectively, as part