What Are the Most Used Extinguishing Agents for Aircraft?

When it comes to safety, there are a lot of requirements that aircraft must meet to create a reasonably prepared environment for emergencies. Fire extinguishers are a common safety protocol in most public places, and a passenger aircraft is no exception. In fact, a strict passenger to portable fire extinguisher ratio must be maintained within most aircraft. Extinguishers are stored in both the cabin and the flight deck, and a variety of materials are used depending on the severity of the fire. This blog will cover the different types of extinguishing agents as well as the ideal situation in which each should be used in flight.

The six types of extinguishing agents used for aircraft are as follows: water, carbon dioxide, dry chemicals, halons, halocarbon clean agents, and specialized dry powder. Fires are classified as one of the following six categories: class A, class B, class C, class D, class E, or class F. However, for the sake of this blog, we will overlook Type E and F fires as they are related to cooking oils and electrical fires. Class A fires are fires that involve solid combustible materials like wood or textiles, so the best extinguishing options are water, dry chemicals, halons, or halocarbon clean agents. While water works to cool these materials below ignition temperature, it should not be used under any other circumstance as it is limited in its extinguishing abilities.

Meanwhile, class B fires occur with flammable liquids and require a blanketing agent like carbon dioxide. Carbon dioxide is an inert cold gas and is frequently used to extinguish fires on the aircraft’s exterior, including APU fires and engine-related fires. It is non-combustible which makes it a safe option, and it is heavier than air, so it smothers fires from directly above. Dry powders also work to extinguish class B fires; however, they leave a great deal or residue. Halons or halocarbons are also good options for quelling class B fires in aircraft as they are extremely effective on a per unit weight basis, nonconductive, low in toxicity, and leave little residue. At the same time, these agents are ozone depleting and global warming chemicals, so they are discouraged in many circumstances. Although it has been banned for many uses across the world, aviation applications of halon are allowed as it is specifically safe when in flight.

Any extinguishing agent used for class B fires can and should be used for class C fires as well. Class C fires involve flammable gasses, so their properties are often similar to those of class B fires. On the other hand, class D fires involve combustible metals and should only be treated with specialized dry powders. These powders take the properties of the specific metal into account and should be utilized as instructed by the manufacturer to avoid hazardous chemical reactions. Aircraft must be prepared for a variety of fires in any location, which is why the many types of extinguishers are stored across the aircraft.

Specific requirements demand that there is one portable fire extinguisher accessible from the seat in the pilot compartment, in addition to one handheld fire extinguisher per 30 passengers. The extinguishers used in personnel compartments must minimize the hazard of toxic gas concentrations, meaning they react safely to extinguish the fire. For this reason, it is important to understand the various types of extinguishing materials and their corresponding fire classes.

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