Fire Extinguishing Agents and Portable Fire Extinguishers - Aircraft Fire Protection Systems | Aircraft Systems

Fire Extinguishing Agents and Portable Fire Extinguishers - Aircraft Fire Protection Systems

There must be at least one hand held, portable fire extinguisher for use in the pilot compartment that is located within easy access of the pilot while seated. There must be at least one hand held fire extinguisher located conveniently in the passenger compartment of each airplane accommodating more than 6 and less than 30 passengers. Each extinguisher for use in a personnel compartment must be designed to minimize the hazard of toxic gas concentrations. The number of portable, hand held fire extinguishers for transport aircraft is shown in Figure 1.

Passenger capacity
No. of extinguishers
7 through 30
1
31 through 60
2
61 through 200
3
201 through 300
4
301 through 400
5
401 through 500
6
501 through 600
7
601 through 700
8
Figure 1. Hand held fire extinguisher requirement for transport aircraft

Halogenated Hydrocarbons

For over 45 years, halogenated hydrocarbons (Halons) have been practically the only fire extinguishing agents used in civil transport aircraft. However, Halon is an ozone depleting and global warming chemical, and its production has been banned by international agreement. Although Halon usage has been banned in some parts of the world, aviation has been granted an exemption because of its unique operational and fire safety requirements. Halon has been the fire extinguishing agent of choice in civil aviation because it is extremely effective on a per unit weight basis over a wide range of aircraft environmental conditions. It is a clean agent (no residue), electrically nonconducting, and has relatively low toxicity.

Two types of Halons are employed in aviation: Halon 1301(CBrF3) a total flooding agent, and Halon 1211 (CBrClF2) a streaming agent. Class A, B, or C fires are appropriately controlled with Halons. However, do not use Halons on a class D fire. Halon agents may react vigorously with the burning metal.

NOTE: While Halons are still in service and are appropriate agents for these classes of fires, the production of these ozone depleting agents has been restricted. Although not required, consider replacing Halon extinguishers with Halon replacement extinguishers when discharged. Halon replacement agents found to be compliant to date include the halocarbons HCFC Blend B, HFC-227ea, and HFC-236fa.

Inert Cold Gases

Carbon dioxide (CO2) is an effective extinguishing agent. It is most often used in fire extinguishers that are available on the ramp to fight fires on the exterior of the aircraft, such as engine or APU fires. CO2 has been used for many years to extinguish flammable fluid fires and fires involving electrical equipment. It is noncombustible and does not react with most substances. It provides its own pressure for discharge from the storage vessel, except in extremely cold climates where a booster charge of nitrogen may be added to winterize the system. Normally, CO2 is a gas, but it is easily liquefied by compression and cooling. After liquification, CO2 remains in a closed container as both liquid and gas. When CO2 is then discharged to the atmosphere, most of the liquid expands to gas. Heat absorbed by the gas during vaporization cools the remaining liquid to –110 °F, and it becomes a finely divided white solid, dry ice snow.

Carbon dioxide is about 1½ times as heavy as air, which gives it the ability to replace air above burning surfaces and maintain a smothering atmosphere. CO2 is effective as an extinguishing agent primarily because it dilutes the air and reduces the oxygen content so that combustion is no longer supported. Under certain conditions, some cooling effect is also realized. CO2 is considered only mildly toxic, but it can cause unconsciousness and death by suffocation if the victim is allowed to breathe CO2 in fire extinguishing concentrations for 20 to 30 minutes. CO2 is not effective as an extinguishing agent on fires involving chemicals containing their own oxygen supply, such as cellulose nitrate (used in some aircraft paints). Also, fires involving magnesium and titanium cannot be extinguished by CO2.

Dry Powders

Class A, B, or C fires can be controlled by dry chemical extinguishing agents. The only all purpose (Class A, B, C rating) dry chemical powder extinguishers contain monoammonium phosphate. All other dry chemical powders have a Class B, C U.S – UL fire rating only. Dry powder chemical extinguishers best control class A, B, and C fire but their use is limited due to residual residue and clean up after deployment.

Water

Class A type fires are best controlled with water by cooling the material below its ignition temperature and soaking the material to prevent re-ignition.

Cockpit and Cabin Interiors fire extinguishers

All materials used in the cockpit and cabin must conform to strict standards to prevent fire. In case of a fire, several types of portable fire extinguishers are available to fight the fire. The most common types are Halon 1211 and water.

Extinguisher Types

Portable fire extinguishers are used to extinguish fires in the cabin or flight deck. Figure 2 shows a Halon fire extinguisher used in a general aviation aircraft. The Halon extinguishers are used on electrical and flammable liquid fires. Some transport aircraft also use water fire extinguisher for use on non-electrical fires.

aircraft fire protection system
Figure 2. Portable fire extinguisher

The following is a list of extinguishing agents and the type (class) fires for which each is appropriate.
  1. Water—class A. Water cools the material below its ignition temperature and soaks it to prevent reignition. 
  2. Carbon dioxide—class B or C. CO2 acts as a blanketing agent. NOTE: CO2 is not recommended for hand-held extinguishers for internal aircraft use. 
  3. Dry chemicals—class A, B, or C. Dry chemicals are the best control agents for these types of fires. 
  4. Halons—only class A, B, or C. 
  5. Halocarbon clean agents—only class A, B, or C. 
  6. Specialized dry powder—class D. (Follow the recommendations of the extinguisher’s manufacturer because of the possible chemical reaction between the burning metal and the extinguishing agent) 

The following hand-held extinguishers are unsuitable as cabin or cockpit equipment.
  • CO2 
  • Dry chemicals (due to the potential for corrosion damage to electronic equipment, the possibility of visual obscuration if the agent were discharged into the flight deck area, and the cleanup problems from their use) 
  • Specialized dry powder ( it is suitable for use in ground operations)