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A fire retardant is a substance that helps to 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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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: 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 example commonly used is the fire retardant, aluminium hydroxide. Not only does it break down to give off water vapor, but it also absorbs a vast amount of heat as it does so, cooling the material, and the residue of alumina (Al2O3) forms a protective layer. It provides protection in three ways at once.
Chemical action
- 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, this class of retardents uses halogens such as bromine or chlorine.
- 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.
- 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
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 FireAde and Arctic Fire are capable of rendering class A material and Class B fuels non-flammable and extinguishing class A,B, and some 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.[2]
Forest-fire fighting
One way that a chemical fire retardant would be used is at a wildfire to try and prevent its spread. A fire retardant would not actually be put directly on the fire in an attempt to extinguish it. Generally, fire retardant is dropped around a fire's edges to contain it, allowing crews time to work to put the fire out while the retardant slowed or prevented further spread. However, when needed, retardant can also be dropped directly onto flames when needed to cool the fire and reduce flame length.[3]
In a forest or wild fire situation in a remote area, a fire retardant would usually be dropped from a plane or helicopter. For example, it would be used on fires up on mountains where there is limited or no ground access. Fire retardants that are used are considered to be non-toxic. However there is little data on the long-terms effects of fire retardant to people or the environment. One of the most-used commercial retardants is Phos-Chek.
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 is usually a mixture of water and chemicals designed to wet the area as well as chemically retard fire progression through vegetation. Typically it is dyed red 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.[4]
See also
- List of fire-retardant materials
- Flame retardant
- Aerial firefighting
- Wildland fire suppression
- Modular Airborne FireFighting System
References
- ^ "U.S. home structure fires". National Fire Protection Association. Retrieved on 2007-08-22.
- ^ 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.
- ^ "CDF Tankers Test Dropping New Colored Retardants" (PDF). California Department of Forestry and Fire Protection (August 27, 2005). Retrieved on 2007-08-22.
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