Understanding Aircraft Fire Extinguishers

An aircraft fire extinguisher is a portable or built-in system used to extinguish or suppress small fires onboard an aircraft. They are essential safety equipment that can help prevent a small fire from escalating into a catastrophic event.

Portable fire extinguishers are small, hand-held extinguishers that are located throughout the cabin and cockpit of an aircraft. They are designed for use by cabin crew or passengers to tackle small fires quickly before they escalate.

Built-in fire extinguishing systems are installed in specific areas of the aircraft, such as engines, APU, and cargo compartments. They are activated automatically by a heat sensor or smoke detector or by the crew in the event of a fire.

Aircraft safety is of utmost importance in aviation, every precaution is taken to protect the passengers, crew, and valuable assets on board the aircraft. Despite careful maintenance and rigorous safety checks, the possibility of fire can pose a major safety hazard.

Different types of fires require specific extinguishing agents and methods to effectively control them. Furthermore, aviation regulatory bodies around the world mandate strict adherence to fire safety standards.

Let’s delve deeper into aviation fires and explore effective methods for extinguishing them.

Potential Causes of Aircraft Fires

In-flight fires in modern aircraft are rare, yet post-crash fires do occur. Here are some common potential reasons that can lead to fires on aircraft.

Engine fires: Engine fires are often caused by excess oil leakage, leaks in fuel lines, overheating of engine components, or uncontrolled engine failures.
Tailpipe Fire: Tailpipe fires occur during ground engine start or shutdown and result from excess fuel in the combustion chamber or turbine area.
Electrical Fires: These originate from faulty or improper electrical components and can be controlled by cutting off power to the affected equipment. The most common cause is broken, frayed, or contaminated insulation.
Short Circuits: Faulty wiring or overloaded circuits can generate heat and sparks, igniting nearby flammable materials such as insulation or electrical panels.
Cargo Fires: Improperly secured or flammable cargo can ignite due to friction, heat, or spontaneous combustion.
Lavatory Fires: Often caused by burning cigarettes placed in the waste paper bin, but electrical equipment inside the lavatory can also pose a fire risk.
Galley Fires: Often related to electrical equipment or oven fires due to inappropriate items being placed inside or overheating of food items.
Smoking: While strictly prohibited onboard, undetected lit cigarettes or embers could potentially start a fire.
Fuel Leaks: Leaks or spills of jet fuel during refueling or maintenance can create a fire hazard if not handled correctly.
Brakes Fire: During landings, brakes can generate significant heat, potentially igniting nearby flammable materials if not functioning properly.
Faulty GSE: Faulty ground support equipment (GSE), such as tugs or generators, can cause a fire.
Battery Fires: Overheating or damage to aircraft batteries can lead to thermal runaway and fires.
PED Fires: Personal Electronic Devices (PEDs) containing lithium batteries, such as laptops or phones, can overheat or malfunction, leading to fires if damaged. They are more likely to be a fire source when in use or being charged.

Requirements for Fire to Occur

Three elements are necessary for fire: fuel, heat, and oxygen. Remove any one of these, and the fire will be extinguished.

FUEL + HEAT + OXYGEN = FIRE

Fuel combines with oxygen in the presence of heat, releasing more heat and reducing itself to other chemical compounds. Heat accelerates this process, while oxygen is the element that chemically combines with another substance through oxidation, resulting in combustion or burning.

To properly understand fire extinguishers for use in an aircraft, it’s essential to familiarize yourself with the classes of fires.

Classification of Fires

For commercial purposes, the National Fire Protection Association (NFPA) has classified fires into three basic types: Class A, Class B, and Class C.

Class A fires involve ordinary combustible materials, such as wood, cloth, paper, upholstery materials, and so forth.
Class B fires involve flammable petroleum products or other flammable or combustible liquids, greases, solvents, paints, and so forth.
Class C fires involve energized electrical wiring and equipment.
Class D fires are not commercially considered by the NFPA to be a basic type of fire since they are caused by a Class A, B, or C fire. Usually, Class D fires involve magnesium in the shop, or in aircraft wheels and brakes, or are the result of improper welding operations.

Fire Extinguishing Systems

Generally, Four types of fire extinguishing systems are used on civil transport aircraft.

Portable extinguishers installed at specified locations in both cabin and cockpit
Cargo compartment fire extinguishing systems
Engine and APU fire extinguishing systems
Toilet waste bin bottle extinguishing systems

Characteristics of Fire Extinguishers

Lightweight and compact: Every pound counts in an aircraft, so extinguishers need to be portable and efficient.
Multipurpose: They should be effective against various fire types commonly encountered in aviation, such as fuel fires, electrical fires, and small galley fires.
Clean and non-corrosive: The extinguishing agent shouldn’t leave behind residues that could damage sensitive aircraft components.
Non-toxic: In the confined space of an airplane, fumes from the extinguisher can pose a danger to occupants if inhaled.

Regulatory Requirements

Regulatory authorities, such as the European Union Aviation Safety Agency (EASA) in the EU and the Federal Aviation Administration (FAA) in the US, establish specific requirements for handheld fire extinguishers, including:

Specifying the minimum number of handheld fire extinguishers required based on factors like aircraft size, passenger seating capacity, and cargo compartment configurations.
Determining the distribution of handheld fire extinguishers throughout the aircraft, including placement in the cockpit, cabin, and cargo compartments.
At least one shall be located in the pilot’s compartment and each passenger compartment that is separate from the pilot’s compartment and that is not readily accessible to the flight crew.
Mandating proper mounting and marking of fire extinguishers to ensure they are easily visible and accessible, such as requiring special signage if an extinguisher is not readily apparent.
Requiring regulatory approval and establishing acceptable means of compliance for fire extinguisher systems.
Imposing restrictions on the types of extinguishing agents permitted, including setting cut-off and end dates for Halon-based extinguishers in compliance with environmental regulations.
Setting requirements for the quantity of extinguishing agent contained within each extinguisher to ensure sufficient capability to combat fires effectively.
Considering health considerations, such as minimizing the potential hazards of toxic gases emitted by extinguishing agents.

Types of Fire Extinguishers

Water fire extinguishers

Water extinguishers are the best type to use on Class A fires.
Water has two effects on fire. It deprives fire of oxygen and cools the material being burned.
Since most petroleum products float on water, water-type fire extinguishers are not recommended for Class B fires.
Extreme caution must be used when fighting electrical fires (Class C) with water-type extinguishers. All electrical power must be removed or shut off to the burning area. Additionally, residual electricity in capacitors, coils, and so forth must be considered to prevent severe injury or possibly death from electrical shock.
Never use water-type fire extinguishers on Class D fires. The cooling effect of water causes an explosive expansion of the metal, because metals burn at extremely high temperatures.

Carbon dioxide (CO2) fire extinguishers

Carbon dioxide (CO2) extinguishers are used for Class A, B, and C fires, extinguishing the fire by depriving it of oxygen.
Like water-type extinguishers, CO2 cools the burning material. Never use CO2 on Class D fires. As with water extinguishers, the cooling effect of CO2 on the hot metal can cause explosive expansion of the metal.

Caution: When using CO2 fire extinguishers, all parts of the extinguisher can become extremely cold, and remain so for a short time after operation. Wear protective equipment or take other precautions to prevent cold injury, such as frostbite. Extreme caution must be used when operating CO2 fire extinguishers in closed or confined areas. Not only can the fire be deprived of oxygen, but so too can the operator.

Halogenated hydrocarbon fire extinguishers

Halogenated hydrocarbon extinguishers are most effective on Class B and C fires. They can be used on Class A and D fires, but they are less effective. Halogenated hydrocarbon, commonly called Freon™ by the industry, are numbered according to chemical formulas with Halon™ numbers.
Two types of Halon extinguishers have been widely used in aviation: Halon 1211 and Halon 1301.

Halon 1211

Bromochlorodifluoromethane (Halon 1211), chemical formula CBrClF2, is a liquefied gas with a UL toxicity rating of 5. It is colorless, noncorrosive, and evaporates rapidly leaving no residue. It does not freeze or cause cold burns and does not harm fabrics, metals, or other materials it contacts. Halon 1211 acts rapidly on fires by producing a heavy blanketing mist that eliminates oxygen from the fire source. More importantly, it interferes chemically with the combustion process of the fire. Furthermore, it has outstanding properties in preventing re-flash after the fire has been extinguished. Halon 1211 discharges as an 85 percent liquid stream offering a long agent throw range.

Halon 1301

Bromotrifluoromethane (Halon 1301), chemical formula CF3Br, is also a liquefied gas and has a UL toxicity rating of 6. It has all the characteristics of Halon 1211. The significant difference between the two is Halon 1211 forms a spray similar to CO2, while Halon 1301 has a vapor spray that is more difficult to direct. Halon 1301 discharges as a gas.

Halon 1211 vs Halon 1301

The differences between Halon 1211 and Halon 1301 primarily lie in their applications. Halon 1211 is used in portable fire extinguishers and is a streaming agent, meaning it is directed at a fire. On the other hand, Halon 1301 is used in fixed installations and is a total flooding agent, meaning it is designed to fill an entire volume (such as a cargo hold or engine compartment) to suppress a fire. Both are effective and widely used, but due to their ozone-depleting properties, the search for alternatives is ongoing.

Please note that crews must be aware that the toxicity of the Halon gases, especially the combination which makes up Halon 1211, is such that use in confined spaces requires care to minimize any inhalation of the discharged gases. It is usually recommended to consider donning a smoke hood before discharge to eliminate this risk.

Dry powder extinguishers

Dry powder extinguishers are best for use on Class D fires.
Also effective on Class B and C fires.
Dry powder is not recommended for aircraft use, except on metal fires, as a fire extinguisher. The leftover chemical residues and dust often make cleanup difficult and can damage electronic or other delicate equipment.

How to Use Fire Extinguishers

Make sure the correct type of fire extinguisher is used when there is a fire.
Stand at a safe distance of 8 feet away from the fire.
Use the PASS Technique to extinguish the fire.

The PASS Technique

The PASS technique is a widely recognized method for using fire extinguishers. It stands for Pull, Aim, Squeeze, Sweep.

Pull: Pull the safety pin to release the locking mechanism and allow the extinguisher to discharge.
Aim: Aim the nozzle of the extinguisher at the base of the fire, not the flames themselves. The base holds the fuel source, and extinguishing it effectively cuts off the fire’s oxygen supply.
Squeeze: Squeeze the trigger or lever firmly and evenly to discharge the extinguishing agent. Maintain a steady grip throughout the discharge.
Sweep: Sweep the extinguisher from side to side until the fire is completely extinguished.

Tip: Before using a fire extinguisher, assess the size and intensity of the fire. If it is spreading rapidly or poses a significant risk, prioritize evacuation. Some types of fires, such as fires involving hazardous materials or fires covering a large area, may require professional intervention.

Inspection of Fire Extinguishers

Proper maintenance and regular inspection of aircraft fire extinguishers are essential to ensure their reliability and effectiveness in an emergency. Utilizing a checklist simplifies this process, but if one is unavailable, the following steps should be taken at a minimum:

Verify the extinguisher is located in its designated position.
Ensure safety seals remain unbroken, indicating readiness for use.
Remove any external dirt and rust to maintain functionality.
Check the gauge or indicator to ensure it falls within the operable range.
Confirm the extinguisher’s weight is appropriate for its type and capacity.
Inspect the nozzle to ensure there are no obstructions that could hinder discharge.
Look for any obvious signs of damage that may compromise the extinguisher’s integrity.

Environmental Concerns with Halon

Halon is an ozone-depleting substance. Halons can destroy ozone molecules very effectively due to their bromine content. They are ten times more potent than chlorofluorocarbons (CFCs) in terms of ozone depletion.

Halogenated hydrocarbons (Halon) have been successfully used for decades by civil aviation for fire extinguishing purposes (halon 1211 and halon 1301), however, it is an ozone-depleting substance that contributes to climate change. Their production has been banned since 1994 with the signing of the Montreal Protocol on Substances That Deplete the Ozone Layer. However, their use has been allowed for certain critical usages, such as for fire protection in aviation, while the industry researches feasible alternatives.

Since the ban, recycled halons have been the only supply of halons in the United States for specialty fire suppression applications.

ICAO has mandated the use of Halon replacements in fire extinguishers used on civil transport aircraft.

Halon Replacement Agents are any clean agents that can be either a non-halon (halocarbon agent) or halon alternative (all other substitute agents) that have SNAP approval by the U.S. EPA and meet the MPS for hand fire extinguishers.

SNAP Program is EPA’s significant new alternatives policy (SNAP) program to evaluate and regulate substitutes for ozone-depleting chemicals that are being phased out under the stratospheric ozone protection provisions of the Clean Air Act.

Refer to 40 CFR Part 82 Subpart G for more details on the SNAP program.

Halon Replacement

While Halon 1301 and 1211 are excellent at extinguishing fires, they have the potential to deplete the ozone layer and contribute to global warming. In response to the cessation of new halon production, alternative clean agents were developed.

It is important that the aircraft stays clean after a fire extinguishing discharge to minimize damage to the aircraft and cargo contained in the compartment. This is especially relevant in case of a spurious discharge when no actual fire occurred.

Many alternatives to halon fire extinguishers have been approved for use in aviation. Here are some of them:

2-BTP (2-bromotrifluoropropene): This is the most common non-halon handheld fire extinguisher agent that is in use on commercial airplanes.
HFC-227ea and HFC-236fa: These are considered acceptable alternative handheld fire extinguishing agents. They have been used to replace Halon 1211 in lavatory waste compartment extinguishers.
HFC-125, Novec 1230 (FK-5-1-12), FIC-13I1, and Powder Aerosol F: These potential halon alternatives have been tested to the draft version of the Minimum Performance Standards (MPS) for Aircraft Engine and APU Compartment Fire Extinguishing Agents.

Safe Use of Halocarbon Extinguishers

Here are some general guidelines for crew members for the safe use of halocarbon extinguishers according to FAA AC 20-42D.

Turn off air recirculation: Immediately turn off all air recirculation systems if permitted by your aircraft flight manual (AFM) or flight crew operations manual (FCOM). Halocarbon agents are much heavier than air and typically stratify at lower levels over time. Turning off the recirculation redirects the agent from low-level air returns to the air outflow valves, expelling it from the aircraft more rapidly. Some aircraft have up to 50% recirculation, so it is important to turn off the air recirculation quickly.
Use Portable Protective Breathing Equipment (PBE): Flight crewmembers should use portable PBE if available and/or as directed by FCOM procedures or AFM. Unprotected personnel should not enter a protected space during or after agent discharge until ventilated. Crew members should follow firefighting procedures when using portable PBE.
Extinguish the Fire and Ventilate the Cabin: Ensure the fire is completely extinguished. To rid the cabin and flight deck of hazardous gases and smoke, ventilate all unpressurized aircraft compartments overboard at the highest possible rate permitted by established crew procedures for your specific aircraft. However, if the fire is not entirely extinguished or if a smoldering fire persists, be cautious when increasing airflow as it may potentially promote fire growth.
Descend to Lower Altitudes: Immediately initiate a descent at the maximum safe rate to 8,000 ft. or to an altitude that is as low as practicable. Descending serves to dilute agent concentration, reduce exposure to both agent and combustion gases, and elevate oxygen concentration. Aircraft with a maximum flying altitude of 12,500 ft. can mitigate hypoxia risk without supplemental oxygen by promptly descending as outlined above.