What is in antique fire extinguishers?

Much like modern ones, antique fire extinguishers used a range of extinguishing agents. Carbon tetrachloride, water, and carbon dioxide were most common.

Carbon tetrachloride is a liquid that was used in glass grenade-type extinguishers or pumped metal extinguishers. While it is quite effective at putting out fires, it is extremely poisonous, and should be disposed of by professionals. This material fights fires by disrupting the chemical chain reaction. When exposed to high temperatures, it can produce phosgene, an insidious poison gas used during both world wars. Halon extinguishers replaced this type, and have, in turn, been replaced by newer clean agents less harmful to the ozone layer.

Water extinguishers were either operated by a hand pump or propelled using a soda-acid system. In the latter, a glass vial containing sulfuric acid was suspended over baking soda. The vial was shattered, spilled, or unplugged by a plunger or other mechanism when the extinguisher was needed. Instructions on this type typically started by telling you to turn the extinguisher upside-down and strike the top against the floor. The sulfuric acid reacted with the baking soda much as vinegar would, only faster and more violently. The resulting carbon-dioxide gas would propel the water, typically 2.5 gallons, out through the hose. This type was removed from service by 1982 because the reaction would often not last long enough to expel all the water and the containers had an unfortunate tendency to explode when used. The similar air pressurized water extinguishers have replaced this type.

Carbon dioxide extinguishers remain in use and are easily identified by the horn used to direct the extinguishing agent and the lack of a pressure gauge. These extinguishers contain liquefied carbon dioxide. While carbon dioxide gas mixed with dry ice is what comes out when you use the extinguisher, internally, the agent is a liquid under those pressures. Because carbon dioxide extinguishers in service, it is possible to have tested and refilled an extinguisher of this type. While an extinguisher has an expected service life of 25 years, they are often overbuilt and underused. I recently had serviced two carbon dioxide extinguishers that were manufactured in 1960, and used from then until 1992. Interestingly, even though they were not entirely full, they retained significant pressure even after having been stored for 18 years.

Some fire extinguishers are simply filled with compressed Nitrogen, which choke out combustion because it cannot survive in a pure Nitrogen atmosphere. The Simplex-Grinnell UN 1066 is such an extinguisher.