Starting about the turn of the 20th century, halon extinguishers, also called green fire extinguishers because of the color of their tank, were commonly used to put out fires on sensitive electrical equipment.
Unlike fire-smothering materials used in other apparatuses, the green extinguishers’ halon had chemical components that left the inner workings of electrical equipment and computers intact while snuffing out the fire on the casings.
Halon was later discovered to have the most detrimental effects on the ozone layer of any known chemical. When ozone-depleting chemicals were put under strict controls in 1993, halon was one of the banned substances.
Despite its toxic threat to the ozone, halon is still used in fire extinguishers on aircraft and in military operations involving fuel installations and vehicle fires. Some countries also approve green fire extinguishers to combat fires in tunnels for trains and other vehicles.