Fire retardant
From Wikipedia, the free encyclopedia
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 over 390,500 homes, and cause just under 6 billion dollars in damage annually. [1] Because of the importance of prevention, fire retardation has become a very important industry.
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[edit] How do fire 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.
[edit] 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, aluminum 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.
[edit] 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 prevent 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.
[edit] Uses
Fire retardants are used in many places to make every day life safer.
[edit] Fire extinguishers
Many different types of fire extinguishers exist. Size and complexity range from small extinguishers meant to be carried in a car up to whole-building chemical extinguishers.
[edit] 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.
[edit] 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. But instead, it would be put around a fire's edges to contain it, this would allow crews time to work to put the fire out while the retardant slowed or prevented further spread.
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.
[edit] Textiles
Most clothing intended for children in the United States is required to pass fire-retardant tests for safety reasons.
[edit] Home furniture
In many locations mattresses are now treated with fire retardant or built with fire-resistant material. Many new foams self-extinguish.
