Fire retardant

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A fire retardant is a substance that helps delay or prevent combustion. Fire retardants are commonly used in fire fighting. Water is the most commonly used fire retardant, but the phrase typically refers to chemical retardants, including fire-fighting foams and fire-retardant gels. It can also refer to a coating over an object, such as a spray retardant to prevent Christmas trees from burning.

Home fires damage about 400,000 homes, and cause just under 7 billion US dollars in direct damage annually in the United States.^[1] Because of the importance of prevention, fire retardation has become a very notable industry.

How retardants work

In general, fire retardants reduce the flammability of materials by either blocking the fire physically or by initiating a chemical reaction that stops the fire.

Physical

There are several ways in which the combustion process can be retarded by physical action:

• By cooling: Some chemical reactions actually cool the material down.
• By forming a protective layer that prevents the underlying material from igniting.
• By dilution: Some retardants release water and/or carbon dioxide while burning. This may dilute the radicals in the flame enough for it to go out.

One commonly used fire retardant coating is aluminium hydroxide. When heated, it dehydrates to form aluminum oxide (alumina, Al₂O₃), releasing water vapor in the process. This reaction absorbs a great deal of heat, cooling the material over which it is coated. Additionally, the residue of alumina forms a protective layer on the material's surface.

Chemical action

• Reactions in the gas phase: chemical reactions in the flame (i.e. gas phase) can be interrupted by fire retardants. Generally, these retardants are organic halides (haloalkanes) such as Halon and PhostrEx. However, there are situations where the released gas might be more dangerous when this type of retardant is involved.

• Reaction in the solid phase: some retardants break down polymers so they melt and flow away from the flame. Although this allows some materials to pass certain flammability tests, there is argument over if the fire safety is truly improved by the production of flammable plastic droplets.

• Char Formation: Solid phase flame retardants are those which cause a layer of carbon char to form on the polymer surface. This carbon char layer is much harder to burn and prevents further burning.^[2]

• Intumescents: These types of retardant materials add chemicals which cause swelling up behind the protective char layer, providing much better insulation behind the protective barrier. In additions to being added to plastics, these are available as paints for protecting wooden buildings or steel structures.

Uses

A Fire extinguisher

Fire extinguishers

Class A foam is used as a fire retardant in 2.5 gallon [APW] and [CAFS] extinguishers to contain incipient brush fires and grass fires by creating a fire break. Other chemical retardants such as FireAide and [Arctic Fire] are capable of rendering class A material and Class B fuels non-flammable and extinguishing class A, class B, and some class D fires. (Fire retardant, such as the slurry dropped from aircraft, is used to prevent ignition while fire suppression agents are used to extinguish fires.)

Surface coating

It is possible to coat an object with a fire retardant. The classic example of this is the green Christmas tree. As a tree dries out it can be accidentally lit on fire putting the home at risk. A coating of a specialised fire retardant can prevent the starting of the fire and slow it down if it does start.

In addition many large sky-scrapers use a coating around main structural elements to prevent catastrophic weakening during a fire. It is believed that one of the reasons why the twin towers collapsed on 9/11 was due to the airplane impact removing portions of the fire-insulation layer.^{[citation needed]}

Many dormitories across the nation are also considering using these products. Since 2000, 109 people have died in fires in dormitories or off-campus student housing across the nation, according to Campus Firewatch, an online newsletter.

Campus Firewatch's publisher, Ed Comeau, said a January 2000 fire at Seton Hall University in New Jersey drew attention to the perils of fire on campus. A common area in a Seton Hall dorm caught fire after two students ignited a banner from a bulletin board. The fire quickly spread to furniture and killed three students and injured 58 others.^[3]

Forest-fire fighting

A MAFFS-equipped Air National Guard C-130 Hercules drops fire retardant on wildfires in Southern California

Red-dyed line of fire retardant stands out clearly on this Arizona hill. Drop was against the Alambre Fire.

Early fire retardants were mixtures of water and thickening agents, and later included borates^[4] and ammonium phosphates.^{[citation needed]}

Generally, fire retardants are dropped from aircraft or applied by ground crews around a wildfire's edges in an effort to contain its spread. This allows ground crews time to work to extinguish the fire. However, when needed, retardant can also be dropped directly onto flames to cool the fire and reduce flame length.^[5]

Aerial firefighting

Aerial firefighting is a method to combat wildfires using aircraft. The types of aircraft used include fixed-wing aircraft and helicopters. Smokejumpers and rappellers are also classified as aerial firefighters, being delivered by parachute from a variety of fixed-wing aircraft, or rappelling from helicopters. Chemicals used to fight fires may include water, water enhancers, or specially-formulated fire retardants.^[6]

Textiles

Most clothing intended for children in the United States is required to pass fire-retardant tests for safety reasons.

Home furniture

In many locations mattresses are now treated with fire retardant or built with fire-resistant material. Many new foams self-extinguish. This is the most common use of fire retardancy in the chemical means.

Materials

Wildfire retardants

Fire retardants applied to wildfires are usually a mixture of water and chemicals designed to wet the area as well as chemically retard a fire's progression through vegetation. Typically it is colored^[7] so that the application area can be seen from the air. New gel-based retardants which meet NFPA Standard 1150 are being introduced into use. These are dyed other colors to differentiate them from the traditional red retardant. The gels and their dyes are designed to biodegrade naturally.^[8] Phos-Chek is a brand of long-term retardant currently approved for wildland fire use.^[9]

Environmental concerns

Some fire retardants contain chemicals that are potentially dangerous to the environment, such as PBDE's. Fire retardants used in airplanes and fire resistant objects such as carpets accumulate in humans. (see PBDE#Health concerns).

Forest fire retardants that are used are generally considered non-toxic,^[10] but even less-toxic compounds carry some risk when organisms are exposed to large amounts.^[11] Fire retardants used in firefighting can be toxic to fish and wildlife as well as firefighters by releasing dioxins and furans when halogenated fire retardants are burned during fires.^[12], and drops within 300 feet of bodies of water are generally prohibited unless lives or property are directly threatened.^[13] The US Forest Service is the governing agency that conducts research and monitors the effect of fire retardants on wildland systems.^[14][15]

See also

• List of fire-retardant materials
• Flame retardant
• Aerial firefighting
• Wildland fire suppression
• Modular Airborne FireFighting System

References

External links

• National Fire Protection Association
• Defense Fire Protection Association
• Using Fire Retardant Materials