Fires are classified into different categories or classes based on the type of materials or substances that are fueling the fire. Understanding the class of fire is crucial for selecting the appropriate firefighting methods and extinguishing agents. Fire extinguishers used in aircraft are typically designed to handle specific classes of fires, and they are chosen based on the fire risks associated with each class.

Class A Fire (Ordinary Fire)

A Class A fire refers to a type of fire that involves ordinary combustible materials. Class A fires are characterized by the presence of materials such as wood, paper, cloth, rubber, and certain types of plastics that can serve as fuel for the fire. These materials leave behind ash when burned.

To suppress a Class A fire, water or water-based fire extinguishing agents are often used. Water works by cooling the burning material and removing heat from the fire, thereby extinguishing it.

For aviation purpose, water can be ineffective at high altitudes or in cold temperatures, so Halon 1211 (a clean agent) or dry chemical extinguishers may also be used.

Class B Fire (Flammable Liquids and Gases)

A Class B fire is a type of fire that involves flammable liquids or gases. These fires are fueled by materials such as gasoline, oil, diesel, kerosene, propane, natural gas, and other similar substances that are typically in a liquid or gaseous state. Class B fires are characterized by the presence of a blue or yellow flame, and they can spread rapidly if not controlled.

To suppress a Class B fire, specialized fire extinguishing agents are used, as water is generally ineffective for this type of fire. Commonly used fire extinguishing agents for Class B fires include Halon 1211 (Halotron), Halon 1301 and Halotron. Halotron is an environmentally friendly alternative to Halon extinguishing agents and is used for Class B fires. It is a clean agent that is effective at suppressing fires without leaving a residue.

Carbon dioxide fire extinguishers can also be used for Class B fires. CO2 displaces oxygen, removing it from the fire and suppressing combustion. Halotron is much more effective than carbon dioxide fire extinguisher.

Class C (Electrical Fires)

Class C fires, which involve energized electrical equipment, require specialized extinguishers that do not conduct electricity. These fires are associated with electrical sources such as wiring, electrical panels, motors, appliances, and other electrical components that may become a fire hazard. Class C fires are unique because they are caused by electrical faults or malfunctions. It’s important to note that water should not be used to suppress Class C fires because it conducts electricity and can lead to electrocution.

Carbon dioxide fire extinguishers are specifically designed for suppressing electrical fires and are effective at removing the oxygen necessary for combustion without causing damage to electrical equipment.

Class D (Metal Fires) Fires

A Class D fire is a type of fire that involves combustible metals, such as magnesium, titanium, sodium, potassium, and other similar materials. These metals have unique properties that make Class D fires different from typical fires involving solid materials. Class D fires can be extremely hot and difficult to extinguish with standard fire suppression methods.

The fire is fueled by combustible metals, which can react violently with water or other typical extinguishing agents, potentially exacerbating the fire. Class D fires often produce a bright white flame, and they can burn at very high temperatures.

Aircraft are not typically at risk of experiencing a Class D fire during normal flight operations. Class D fires involve combustible metals, and the materials used in aircraft construction and operation are not typically made of these metals. Aircraft are designed and built with a variety of non-combustible or fire-resistant materials, including aluminum, titanium, and composite materials.

However, there are certain situations in which a Class D fire could potentially occur in or near an aircraft, though they are extremely rare. These situations may be associated with cargo carried or aircraft maintenance work being done on components or systems containing combustible metals.

Class K (Kitchen Fires) Fires

A Class K fire is a type of fire that occurs in commercial kitchens and involves cooking oils, fats, and greases. These fires are unique because the burning materials are typically found in cooking appliances like deep fryers, griddles, and stovetops, and they can reach very high temperatures. Class K fires are especially common in restaurant kitchens and other food service establishments.

Class K fire is not associated with aircraft.

Halon 1211 – Portable Fire Extinguishers in Aircrafts

Portable fire extinguishers pose a unique challenge, as they must be versatile enough to combat various types of fires, including those involving solid materials like cabin fixtures and furnishings, flammable liquids, and electrical equipment.

Halon 1211 extinguishers have entirely replaced the need for a combination of two different types of portable extinguishers, namely carbon dioxide and water glycol, in the construction of new aircraft. No other single extinguisher type has been identified as a satisfactory alternative to Halon 1211.

It’s crucial for crews to be aware that Halon gases, especially the combination found in Halon 1211, can be toxic. Therefore, when using a portable Halon extinguisher in confined spaces, precautions should be taken to minimize the inhalation of the discharged gases. For cabin crew members, it’s typically recommended to wear a smoke hood before discharging the extinguisher to eliminate this risk. However, for flight crew members on the flight deck, this option may or may not be available, making risk awareness their primary defense.