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Fire retardant dispersed aerially onto brush adjoining a firebreak to contain the Tumbleweed Fire in California, in July 2021

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 of fuels or delay their combustion.[1][2] Fire retardants may also cool the fuel through physical action or endothermic chemical reactions. Fire retardants are available as powder, to be mixed with water, as fire-fighting foams and fire-retardant gels. Fire retardants are also available as coatings or sprays to be applied to an object.[3]

Fire retardants are commonly used in fire fighting, 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 that stops the fire.

Physical action

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

Commonly used fire retardant additives include mixtures of huntite and hydromagnesite, aluminium hydroxide, and magnesium hydroxide. When heated, aluminium hydroxide dehydrates to form aluminum oxide (alumina, Al2O3), releasing water vapor in the process. This reaction absorbs a great deal of heat, cooling the material into which it is incorporated. Additionally, the residue of alumina forms a protective layer on the material's surface. Mixtures of huntite and hydromagnesite work in a similar manner. They endothermically decompose releasing both water and carbon dioxide,[4][5] giving fire retardant properties[6][7][8] to the materials in which they are incorporated.

Chemical action


Portable 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 are capable of rendering class A material and Class B fuels non-flammable and extinguishing class A, class B, and some class D fires.[citation needed] Fire retardant slurries dropped from aircraft are normally applied ahead of a wildfire 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 structures have a fire retardant coating around columns and beams to prevent structural elements from weakening during a fire.

Dormitories in the US are also considering using these products.[citation needed] 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.[when?] 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.[11]

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, to control the Alambre Fire

Early fire retardants were mixtures of water and thickening agents, and later included borates[12] 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.[13]

Aerial firefighting

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.[14]


Main articles: Flame retardant and Fire-retardant fabrics


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[15] 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.[16]

Any fire retardant approved for use against wildfires on US Federal lands must be included on the United States Forest Service Qualified Products List.[17] 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, a process that can take up to two years.[18] Phos-Chek is a brand of long-term retardant currently approved for wildland fire use.[19] 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.[20] 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.[21]

Environmental concerns

Forest fire retardants that are used are generally considered non-toxic,[22] but even less-toxic compounds carry some risk when organisms are exposed to large amounts.[23] Fire retardants used in firefighting can be toxic to fish and wildlife as well as firefighters[24] by releasing dioxins and furans when halogenated fire retardants are burned during fires,[25] and drops within 300 feet of bodies of water are generally prohibited unless lives or property are directly threatened.[26] The US Forest Service is the governing agency that conducts research and monitors the effect of fire retardants on wildland systems in the US.[27][28]

A study published in June 2014 found that marine bacteria have the ability to manufacture a non-synthetic source of chemically identical polybrominated diphenyl ethers (PBDEs). These chemicals are used as flame retardant, but are known to be toxic to the environment.[29]

Potential risk and health concerns


Most chemical fire retardants are organic halides (haloalkanes) such as Halon and PhostrEx, which are proven to be toxic. During 1980s, the most commonly used fire retardant material was penta-bromodiphenyl ether. It was banned by the US Government due to its potential health and environment concerns. It was then replaced by chlorinated tris, chloroalkyl phosphates, halogenated aryl esters, and tetrabromophthalate diol diester, which later were proven by an EPA study that they contained mutagens that could be absorbed into children's bodies.[30]

Studies have shown that a small percentage of the population may have an allergy towards the chemical substance used as fire retardant.[31] Studies have also shown that a drop of the retardant chemical directly into a stream may cause a sufficient ammonia concentration in the water, which is lethal to fish and other aquatic organisms.[32] If the amount is large enough, there is a risk that it could lead to lethal consequences towards humans.

Health concerns

Long-term exposure to these chemicals are likely to develop cancer or skin disease for fire fighters, and the potential contamination towards the environment will be another safety concern.[33] Many of these chemicals are now recognized as global contaminants and are associated with adverse health effects in animals and humans, including endocrine and thyroid disruption, immunotoxicity, reproductive toxicity, cancer, and adverse effects on fetal and child development and neurologic function.[34]

One of the most common way to spread fire retardant is through aerial firefighting, which means that there are chances that these toxic chemicals will contaminate the soil and water system, and then find their way into human body. This will lead to the likelihood of developing long-term health issues, such as respiratory disease or other risky health concerns.[35]

Another notable health concern is that fire-suppressant foams are toxic in standardized soft and hard water, and it is likely that water creatures will be infected. If they were to be consumed by humans, there is a great chance that these toxicities will be transferred into human body.[36]

See also


  1. ^ "BLM Wyoming Wildland Fire Glossary". 2008-06-18. Archived from the original on 2014-05-08. Retrieved 2012-08-04.
  2. ^ Coford Glossary "Fire Retardant" Archived February 8, 2009, at the Wayback Machine
  3. ^ "Zinsser Glossary". Retrieved 2012-08-04.
  4. ^ Hollingbery, LA; Hull TR (2010). "The Thermal Decomposition of Huntite and Hydromagnesite - A Review". Thermochimica Acta. 509 (1–2): 1–11. doi:10.1016/j.tca.2010.06.012.
  5. ^ Hollingbery, LA; Hull TR (2012). "The Thermal Decomposition of Natural Mixtures of Huntite and Hydromagnesite". Thermochimica Acta. 528: 45–52. doi:10.1016/j.tca.2011.11.002.
  6. ^ Hollingbery, LA; Hull TR (2010). "The Fire Retardant Behaviour of Huntite and Hydromagnesite - A Review". Polymer Degradation and Stability. 95 (12): 2213–2225. doi:10.1016/j.polymdegradstab.2010.08.019.
  7. ^ Hollingbery, LA; Hull TR (2012). "The Fire Retardant Effects of Huntite in Natural Mixtures with Hydromagnesite". Polymer Degradation and Stability. 97 (4): 504–512. doi:10.1016/j.polymdegradstab.2012.01.024.
  8. ^ Hull, TR; Witkowski A; Hollingbery LA (2011). "Fire Retardant Action of Mineral Fillers". Polymer Degradation and Stability. 96 (8): 1462–1469. doi:10.1016/j.polymdegradstab.2011.05.006. S2CID 96208830.
  9. ^ "PHOS-CHeK D75 Fire Retardants" (PDF). Archived from the original (PDF) on 2011-07-15. Retrieved 2008-11-20.
  10. ^ "How do flame retardants work?". European Chemical Industry Council (CEFIC) and European Flame Retardants Association (EFRA). Retrieved 12 Feb 2010.
  11. ^ Amy Farnsworth (2007-08-06). "New coatings cut risk of a dorm fire". The Boston Globe.
  12. ^ US 2858895, Connell, George A. (inventor), "Methods and compositions for controlling fires", published November 4, 1958 .
  13. ^ "Interagency Standards for Fire and Aviation Operations 2007, Chapter 17" (PDF). National Interagency Fire Center. Archived from the original (PDF) on 2007-09-28. Retrieved 2007-08-31.
  14. ^ "USDA Forest Service Wildland Fire Chemicals". Retrieved 2008-11-13.
  15. ^ US 6676858, Vandersall, Howard L. & Kegeler, Gary H., "Colorant liquid, method of use, and wildfire retardant liquids containing the same", published January 13, 2004 .
  16. ^ "New fire retardant gel developed that can remain effective for months". 4 October 2019. Retrieved 2020-10-05.
  17. ^ Qualified Products List
  18. ^ "Long-Term Fire Retardants - National Technology and Development Program - USDA Forest Service". Retrieved 2022-01-06.
  19. ^ "Wildland Fire Chemical Product Information". Retrieved 2008-11-13.
  20. ^ "Phos-Chek Wildfire Home Defense FAQs". Retrieved 2019-09-13.
  21. ^ "Ember bloc fire gel fact sheet / Technical specs". Retrieved 2020-10-05.
  22. ^ "Phos-Chek MSDS" (PDF). Retrieved 2008-11-14.[permanent dead link]
  23. ^ Bell, Tina; Tolhurst, Kevin; Wouters, Michael (16 May 2005). "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". International Journal of Wildland Fire. 14 (2): 199–211. doi:10.1071/WF04024. S2CID 129368588.
  24. ^ "". Archived from the original on 2012-02-20. Retrieved 2012-08-04.
  25. ^ "Effect of Fire Retardant on Water Quality" (PDF). Retrieved 2008-11-17.
  26. ^ William Yardley (November 15, 2008). "In Fighting Wildfires, Concerns About Chemicals". The New York Times. Retrieved 2008-11-26.
  27. ^ "USDA Forest Service Wildland Fire Chemical Systems". Retrieved 2008-11-13.
  28. ^ "Wildland Fire Chemical Products Toxicity and Environmental Concerns" (PDF). Retrieved 2008-11-13.
  29. ^ "Marine bacteria are natural source of chemical fire retardants". June 29, 2014. Retrieved July 21, 2017.
  30. ^ Lorber, Matthew (January 2008). "Exposure of Americans to polybrominated diphenyl ethers". Journal of Exposure Science & Environmental Epidemiology. 18 (1): 2–19. doi:10.1038/sj.jes.7500572. ISSN 1559-064X. PMID 17426733. S2CID 27473105.
  31. ^ Bakker, Martine I.; de Winter-Sorkina, Renata; de Mul, Anika; Boon, Polly E.; van Donkersgoed, Gerda; van Klaveren, Jacob D.; Baumann, Bert A.; Hijman, Willie C.; van Leeuwen, Stefan P. J.; de Boer, Jacob; Zeilmaker, Marco J. (February 2008). "Dietary intake and risk evaluation of polybrominated diphenyl ethers in The Netherlands". Molecular Nutrition & Food Research. 52 (2): 204–216. doi:10.1002/mnfr.200700112. ISSN 1613-4133. PMID 18058856.
  32. ^ Dietrich, Joseph P.; Myers, Mark S.; Strickland, Stacy A.; Van Gaest, Ahna; Arkoosh, Mary R. (January 2013). "Toxicity of forest fire retardant chemicals to stream-type chinook salmon undergoing parr-smolt transformation". Environmental Toxicology and Chemistry. 32 (1): 236–247. doi:10.1002/etc.2052. ISSN 1552-8618. PMID 23161484. S2CID 5240730.
  33. ^ Shaw, Susan D.; Blum, Arlene; Weber, Roland; Kannan, Kurunthachalam; Rich, David; Lucas, Donald; Koshland, Catherine P.; Dobraca, Dina; Hanson, Sarah; Birnbaum, Linda S. (October 2010). "Halogenated flame retardants: do the fire safety benefits justify the risks?". Reviews on Environmental Health. 25 (4): 261–305. doi:10.1515/reveh.2010.25.4.261. ISSN 0048-7554. PMID 21268442. S2CID 20573319.
  34. ^ Shaw, Susan D.; Blum, Arlene; Weber, Roland; Kannan, Kurunthachalam; Rich, David; Lucas, Donald; Koshland, Catherine P.; Dobraca, Dina; Hanson, Sarah; Birnbaum, Linda S. (October 2010). "Halogenated flame retardants: do the fire safety benefits justify the risks?". Reviews on Environmental Health. 25 (4): 261–305. doi:10.1515/reveh.2010.25.4.261. ISSN 0048-7554. PMID 21268442. S2CID 20573319.
  35. ^ Sugeng, Eva J.; de Cock, Marijke; Schoonmade, Linda J.; van de Bor, Margot (October 2017). "Toddler exposure to flame retardant chemicals: Magnitude, health concern and potential risk- or protective factors of exposure: Observational studies summarized in a systematic review". Chemosphere. 184: 820–831. Bibcode:2017Chmsp.184..820S. doi:10.1016/j.chemosphere.2017.06.041. ISSN 1879-1298. PMID 28645086.
  36. ^ Gaikowski, M. P.; Hamilton, S. J.; Buhl, K. J.; McDonald, S. F.; Summers, C. H. (August 1996). "Acute toxicity of firefighting chemical formulations to four life stages of fathead minnow". Ecotoxicology and Environmental Safety. 34 (3): 252–263. doi:10.1006/eesa.1996.0070. ISSN 0147-6513. PMID 8812194.