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. 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 important industry.
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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.
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: This protects the remaining material.
- 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.
- Reactions in the gas phase: chemical reactions in the flame (i.e. gas phase) can be interrupted by fire retardants. However, there are situations where the released gas might be more dangerous when this type of retardant is involved. Generally, these retardants are organic halides (haloalkanes) such as Halon and PhostrEx.
- Reaction in the solid phase: This kind of flame retardant works by breaking down the plastics polymer so it melts and flows away from the flame. Although this allows 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.
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.)
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]
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.[4]
- See also: 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.[5]
Most clothing intended for children in the United States is required to pass fire-retardant tests for safety reasons.
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.
Fire retardants applied to wildfires are usually a mixture of water and chemicals designed to wet the area as well as chemically retard fire progression through vegetation. Typically it is colored 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.[6] Phos-Chek is a brand of long-term retardant currently approved for wildland fire use.[7]
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.[citation needed]
Forest fire retardants that are used are generally considered non-toxic,[8] but even less-toxic compounds carry some risk when organisms are exposed to large amounts.[9] Fire retardants used in firefighting can be toxic to fish and wildlife[10], including humans, and as such, drops over bodies of water are prohibited in the US except in emergencies.[citation needed] The US Forest Service is the governing agency that conducts research and monitors the effect of fire retardants on wildland systems.[11][12]
- List of fire-retardant materials
- Flame retardant
- Aerial firefighting
- Wildland fire suppression
- Modular Airborne FireFighting System
- ^ "U.S. home structure fires". National Fire Protection Association. Retrieved on 2007-08-22.
- ^ "PHOS-CHeK® D75 Fire Retardants". Retrieved on 2008-11-20.
- ^ New coatings cut risk of a dorm fire - The Boston Globe
- ^ "Interagency Standards for Fire and Aviation Operations 2007, Chapter 17" (PDF). National Interagency Fire Center. Retrieved on 2007-08-31.
- ^ "USDA Forest Service Wildland Fire Chemicals". Retrieved on 2008-11-13.
- ^ "CDF Tankers Test Dropping New Colored Retardants" (PDF). California Department of Forestry and Fire Protection (August 27, 2005). Retrieved on 2007-08-22.
- ^ "Wildland Fire Chemical Product Information". Retrieved on 2008-11-13.
- ^ "Phos-Chek MSDS". Retrieved on 2008-11-14.
- ^ "Bell, T, Tolhurst, K, and Wouters, M. Effects of the fire retardant Phos-Chek on vegetation in eastern Australian heathlands. International Journal of Wildland Fire. 14(2) 199–211.".
- ^ "Effect of Fire Retardant on Water Quality".
- ^ "USDA Forest Service Wildland Fire Chemical Systems". Retrieved on 2008-11-13.
- ^ "Wildland Fire Chemical Products Toxicity and Environmental Concerns" (PDF). Retrieved on 2008-11-13.
