A fire retardant is a substance that is used to slow down or stop the spread of fire or reduce its intensity. This is commonly accomplished by chemical reactions that reduce the

flammability A combustible material is a material that can burn (i.e., sustain a flame) in air under certain conditions. A material is flammable if it ignites easily at ambient temperatures. In other words, a combustible material ignites with some effort a ...

of fuels or delay their

combustion Combustion, or burning, is a high-temperature exothermic redox chemical reaction between a fuel (the reductant) and an oxidant, usually atmospheric oxygen, that produces oxidized, often gaseous products, in a mixture termed as smoke. Combustion ...

. Fire retardants may also cool the fuel through physical action or

endothermic An endothermic process is a chemical or physical process that absorbs heat from its surroundings. In terms of thermodynamics, it is a thermodynamic process with an increase in the enthalpy (or internal energy ) of the system.Oxtoby, D. W; Gillis, ...

chemical reactions. Fire retardants are available as powder, to be mixed with water, as

fire-fighting foam Firefighting foam is a foam used for fire suppression systems, fire suppression. Its role is to cool the fire and to coat the fuel, preventing its contact with oxygen, thus achieving suppression of the combustion. Firefighting foam was invented b ...

s and

fire-retardant gel Fire-retardant gels are superabsorbent polymer slurries with a "consistency almost like petroleum jelly." Fire-retardant gels can also be slurries that are composed of a combination of water, starch, and clay. Used as fire retardants, they can ...

s. Fire retardants are commonly used in

fire fighting Firefighting is a profession aimed at controlling and extinguishing fire. A person who engages in firefighting is known as a firefighter or fireman. Firefighters typically undergo a high degree of technical training. This involves structural fir ...

, where they may be applied aerially or from the ground.

Principles of operation

In general, fire retardants reduce the flammability of materials by either blocking the fire physically or by initiating a

chemical reaction A chemical reaction is a process that leads to the chemistry, chemical transformation of one set of chemical substances to another. When chemical reactions occur, the atoms are rearranged and the reaction is accompanied by an Gibbs free energy, ...

that stops the fire.

Physical action

There are several ways in which the

process can be retarded by physical action: * By

cooling Cooling is removal of heat, usually resulting in a lower temperature and/or Phase transition, phase change. Temperature lowering achieved by any other means may also be called cooling. The Heat transfer, transfer of Internal energy, thermal energ ...

: 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 Water is an inorganic compound with the chemical formula . It is a transparent, tasteless, odorless, and Color of water, nearly colorless chemical substance. It is the main constituent of Earth's hydrosphere and the fluids of all known liv ...

and/or

carbon dioxide Carbon dioxide is a chemical compound with the chemical formula . It is made up of molecules that each have one carbon atom covalent bond, covalently double bonded to two oxygen atoms. It is found in a gas state at room temperature and at norma ...

while burning. This may dilute the

radicals Radical (from Latin: ', root) may refer to: Politics and ideology Politics *Classical radicalism, the Radical Movement that began in late 18th century Britain and spread to continental Europe and Latin America in the 19th century *Radical politics ...

in the flame enough for it to go out. Commonly used fire retardant additives include mixtures of

huntite Huntite is a carbonate mineral with the chemical formula Mg3Ca(CO3)4. Huntite crystallizes in the trigonal system and typically occurs as platy crystals and powdery masses. For most of recorded history its main use was as a white pigment. Today ...

() and

hydromagnesite Hydromagnesite is a hydrated magnesium carbonate mineral with the formula . It generally occurs associated with the weathering products of magnesium containing minerals such as serpentine group, serpentine or brucite. It occurs as incrustations a ...

(),

aluminium hydroxide Aluminium hydroxide, , is found as the mineral gibbsite (also known as hydrargillite) and its three much rarer polymorphs: bayerite, doyleite, and nordstrandite. Aluminium hydroxide is amphoteric, i.e., it has both basic and acidic propert ...

(), and

magnesium hydroxide Magnesium hydroxide is an inorganic compound with the chemical formula Mg(OH)2. It occurs in nature as the mineral brucite. It is a white solid with low solubility in water (). Magnesium hydroxide is a common component of antacids, such as milk o ...

(). When heated,

dehydrates to form

aluminum oxide Aluminium oxide (or aluminium(III) oxide) is a chemical compound of aluminium and oxygen with the chemical formula . It is the most commonly occurring of several aluminium oxides, and specifically identified as aluminium oxide. It is commonly ...

(alumina, , releasing water vapor in the process. This reaction absorbs a great deal of

heat In thermodynamics, heat is energy in transfer between a thermodynamic system and its surroundings by such mechanisms as thermal conduction, electromagnetic radiation, and friction, which are microscopic in nature, involving sub-atomic, ato ...

, cooling the material into which it is incorporated. Additionally, alumina residue forms a protective layer on the material's surface. Mixtures of

and

work in a similar manner. They endothermically decompose releasing both water and carbon dioxide, giving fire retardant properties to the materials in which they are incorporated.

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 halide Halocarbon compounds are Chemical compound, chemical compounds in which one or more carbon atoms are linked by covalent bonds with one or more halogen atoms (fluorine, chlorine, bromine or iodine – ) resulting in the formation of organofluor ...

s (

haloalkane The haloalkanes (also known as halogenoalkanes or alkyl halides) are alkanes containing one or more halogen substituents of hydrogen atom. They are a subset of the general class of halocarbons, although the distinction is not often made. Haloalka ...

s) such as

Halon Halon may refer to: * Haloalkane, or halogenoalkane, a group of chemical compounds consisting of alkanes with linked halogens (in particular, bromine-containing haloalkanes) * Halomethane compounds: ** Halon 10001 (iodomethane) ** Halon 1001 (bromo ...

and

PhostrEx PhostrEx is a fire suppression agent developed for use in aviation applications to replace halon, a greenhouse gas (GHG). It was developed by Eclipse Aviation for use aboard their Eclipse 500 very light jets as an engine fire suppression system, a ...

. The chemicals used in these types of retardants are often toxic. * Reaction in the solid phase: some retardants break down

polymer A polymer () is a chemical substance, substance or material that consists of very large molecules, or macromolecules, that are constituted by many repeat unit, repeating subunits derived from one or more species of monomers. Due to their br ...

s so they melt and flow away from the flame. Although this allows some materials to pass certain flammability tests, it is not known whether fire safety is truly improved by the production of flammable

plastic Plastics are a wide range of synthetic polymers, synthetic or Semisynthesis, semisynthetic materials composed primarily of Polymer, polymers. Their defining characteristic, Plasticity (physics), plasticity, allows them to be Injection moulding ...

droplets. * Char Formation: For carbon-based fuels, solid phase flame retardants cause a layer of

carbon Carbon () is a chemical element; it has chemical symbol, symbol C and atomic number 6. It is nonmetallic and tetravalence, tetravalent—meaning that its atoms are able to form up to four covalent bonds due to its valence shell exhibiting 4 ...

aceous char to form on the fuel surface. This char layer is much harder to burn and prevents further burning. *

Intumescent An intumescent substance is one that swells as a result of heat exposure, leading to an increase in volume and decrease in density. Intumescence refers to the process of swelling. Intumescent materials are typically used in passive fire protectio ...

s: These types of retardant materials incorporate chemicals which cause swelling behind the protective char layer, providing much better

insulation Insulation may refer to: Thermal * Thermal insulation, use of materials to reduce rates of heat transfer ** List of insulation materials ** Building insulation, thermal insulation added to buildings for comfort and energy efficiency *** Insulated ...

. They are available as plastic additives, and 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 PWand AFSextinguishers to contain incipient brush fires and grass fires by creating a fire break. Other chemical retardants 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 slurries dropped from aircraft are normally applied ahead of a

wildfire A wildfire, forest fire, or a bushfire is an unplanned and uncontrolled fire in an area of Combustibility and flammability, combustible vegetation. Depending on the type of vegetation present, a wildfire may be more specifically identified as a ...

to prevent ignition, while fire suppression agents are used to extinguish fires.

Surface coating

Objects may be coated with fire retardants. For example, Christmas trees are sprayed with retardants, as a tree dries out it becomes very flammable and a fire-hazard.

Steel Steel is an alloy of iron and carbon that demonstrates improved mechanical properties compared to the pure form of iron. Due to steel's high Young's modulus, elastic modulus, Yield (engineering), yield strength, Fracture, fracture strength a ...

structures have a fire retardant coating around columns and beams to prevent structural elements from weakening during a fire. Dormitories in the US are considering or are required by law to use these products.

coatings are used by various dormitories and in school buildings, especially those with historic structures that lack

fire sprinkler system A fire sprinkler system is an active fire protection method, consisting of a water supply system providing adequate pressure and flowrate to a water distribution piping system, to which fire sprinklers are connected. Although initially used on ...

Forest-fire fighting

Hercules C130 bombardier d eau Californie

Early fire retardants were mixtures of water and thickening agents, and later included

borate A borate is any of a range of boron oxyanions, anions containing boron and oxygen, such as orthoborate , metaborate , or tetraborate ; or any salt of such anions, such as sodium metaborate, and borax . The name also refers to esters of su ...

s and ammonium phosphates. Generally, fire retardants are dropped from aircraft or applied by ground crews around a

'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.

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.

Textiles

Materials

Wildfire retardants

Fire retardants applied to

s 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 so that the application area can be seen from the air. Fire retardant gel based retardants which meet NFPA Standard 1150 are also being used in service. These are dyed other colors to differentiate them from the traditional red retardant. The gels and their dyes are designed to biodegrade naturally. Phos-Chek Tank

Any fire retardant approved for use against wildfires on US Federal lands must be included on the United States Forest Service Qualified Products List. To be added to that list, the product must be tested by Wildland Fire Chemical Systems, a division of the National Technology and Development Program. This process can take up to two years.

Phos-Chek Phos-Chek is a brand of long-term fire retardants, class A foams, and gels manufactured by Perimeter Solutions, headquartered in Clayton, Missouri, United States. Products Fire retardants Phos-Chek fire retardants are manufactured as dr ...

is a brand of long-term retardant currently approved for wildland fire use. Researchers at the

University of Southern California The University of Southern California (USC, SC, or Southern Cal) is a Private university, private research university in Los Angeles, California, United States. Founded in 1880 by Robert M. Widney, it is the oldest private research university in ...

’s Department of Civil and Environmental Engineering published a report titled �
Metals in Wildfire Suppressants
” The report provides the first-ever chemical analysis of Phos-Chek fire retardant, which the research team studied because it is the most widely used. The USC researchers found that Phos-Chek contains high levels of heavy metals: 14,400 μg/l of cadmium, 72,700 μg/l of chromium, and 119,000 μg/l of vanadium. These numbers exceed California toxic waste limits by 14 times, 14 times, and five times, respectively. Phos-Chek also has a consumer-based fire retardant spray called Wildfire Home Defense that is effective immediately after application and that remains effective until it is washed off with heavy water levels. It is designed to be applied to fuel beds around homes and outbuildings to create a firebreak in the fuels leading up to each structure. Ember Bloc is another consumer-based fire retardant gel that can be applied to the exterior of one's house and nearby structures to help protect against both embers and flames in a wildfire. It has a unique ability to cling onto the side of a house to withstand high heat and windy conditions.

Environmental concerns

Forest fire retardants that are used are generally considered

non-toxic Toxicity is the degree to which a chemical substance or a particular mixture of substances can damage an organism. Toxicity can refer to the effect on a whole organism, such as an animal, bacteria, bacterium, or plant, as well as the effect o ...

, but even less-toxic compounds carry some risk when organisms are exposed to large amounts. As of 2008, drops within 300 feet of bodies of water are generally discouraged unless lives or property are directly threatened. The

US Forest Service The United States Forest Service (USFS) is an agency within the U.S. Department of Agriculture. It administers the nation's 154 national forests and 20 national grasslands covering of land. The major divisions of the agency are the Chief's ...

is the governing agency that conducts research and monitors the effect of fire retardants on wildland systems in the US.

Potential risk and health concerns

Some specialized indoor fire retardants are organic halides (haloalkanes) such as

and

, which are proven to be toxic. Studies have also shown that a drop of the retardant chemical directly into a stream may cause a sufficient

ammonia Ammonia is an inorganic chemical compound of nitrogen and hydrogen with the chemical formula, formula . A Binary compounds of hydrogen, stable binary hydride and the simplest pnictogen hydride, ammonia is a colourless gas with a distinctive pu ...

concentration in the water, which is

lethal Lethality (also called deadliness or perniciousness) is how capable something is of causing death. Most often it is used when referring to diseases, chemical weapons, biological weapons, or their toxic chemical components. The use of this term ...

to fish and other

aquatic organism An aquatic ecosystem is an ecosystem found in and around a body of water, in contrast to land-based terrestrial ecosystems. Aquatic ecosystems contain communities of organisms—aquatic life—that are dependent on each other and on their environm ...

s. Another notable health concern is that fire-suppressant foams are especially toxic to fish in standardized soft and

hard water Hard water is water that has a high mineral content (in contrast with "soft water"). Hard water is formed when water percolates through deposits of limestone, chalk or gypsum, which are largely made up of calcium and magnesium carbonates, bic ...

, possibly due to surfactants.

References

External links

Fire Management Notes (1989)

National Fire Protection Association

Defense Fire Protection Association

Influence of the fire retardant, ammonium polyphosphate, on the thermal degradation of poly(methyl methacrylate)

Fire retardant Glass
– UL9 Certified Fire Resistant glass in USA {{DEFAULTSORT:Fire Retardant Fire protection Fire suppression agents Wildfire suppression Aerial firefighting Occupational safety and health