FLAME RETARDANTS
FLAME RETARDANTS
Flame retardants refer to a variety of substances that are added to combustible materials to prevent fires from starting or to slow the spread of fire and provide additional escape time.
The term “flame retardant” refers to a function, not a family of chemicals.
A variety of different chemistries, with different properties and molecular structures, act as flame retardants and these chemicals are often combined for effectiveness.
Fire retardants that are halogen-free are preferred in the market.
Flame retardants help to save lives by slowing down or stopping the spread of fire or reducing its intensity.
Also called fire retardants, they are used in anything from phones and curtains to car seats and buildings.
If a fire starts, they may be able to stop it completely – or slow it down and so provide precious extra time for escape.
With our non-halogenated, phosphorus-based flame retardants, you add more than reliable fire resistance to materials, products and coatings
Halogen-free flame retardants have been developed to lower the smoke toxicity and to prevent the migration of the additives.
How do flame retardants reduce the impact of fires on people, property and the environment?
In an early stage of the ignition process, flame retardants can substantially contribute to extinguishing a smoldering fire (e.g., overheated electric device). At a later stage of fire—or when the fire is spreading too strong or too fast-the flame retardants cannot stop the flashover of a fire anymore.
However, they can limit the impact and damage (e.g., flame retardant curtains not catching fire rapidly). And, providing a very important benefit, they can save human lives by increasing the time available for people to escape the fire (e.g., flame retardant-equipped plastics in public transportation).
What are the advantages of halogen-free flame retardants over halogenated alternatives?
Conventional halogenated flame retardants do their job. It’s clear. But the “Achilles heel” of these chemicals are their toxicity and their side effects: On the one hand some of these additives are listed as Substances of Very High Concern (SVHC).
On the other hand a fire can release many toxic substances from halogenated flame retardants, like brominated dioxins and furans.
In addition, halogenated flame retardants are commonly used together with antimony trioxide.
Halogen-free flame retardants have been developed to lower the smoke toxicity and to prevent the migration of the additives.
Furthermore, there is no compromise in flame retardancy and little impact on technical parameters of the final application.
In the meantime, rethinking leads to a significant variety of halogen-free flame retardants, most often tailor-made for individual polymers and applications.
When added to different materials, flame retardants can help prevent fires from starting or limit their spread.
According to the U.S. Fire Administration and the National Fire Protection Association (NFPA), in 2019 an estimated 1.3 million fires were reported in the United States, causing 3,700 civilian fire deaths, 16,600 civilian injuries and $14.8 billion in property damage.
The use of flame retardants is especially important today, as the large volume of electrical and electronic equipment in today’s buildings, coupled with a larger volume of combustible materials, can increase the potential for fire hazards
Flame retardants provide consumers with a critical layer of fire protection and can be vital to reducing the risks associated with fire.
Today, flame retardants are typically used in four major areas: electronics and electrical devices, building and construction materials, furnishings and transportation.
Electronics and Electrical Devices
Flame retardants can enable modern electronic equipment, like televisions and computers, to meet fire safety standards and can be vital to the safety of hundreds of these products.
Building and Construction Materials
Flame retardants used in a variety of building and construction materials in homes, offices and public buildings, including schools and hospitals, can provide increased fire safety protection.
Furnishings
The addition of flame retardants to the material fillings and fibers used in furnishings helps provide individuals with an extra layer of fire protection and can increase critical escape time in case of a fire.
Transportation
From airplanes to cars to trains, flame retardants can play a key role in protecting travelers from the devastation of fire.
After the July 2013 Asiana Airline crash in San Francisco, for example, experts credited flame retardant materials with helping passengers survive the crash.
As former FAA Director Steven Wallace told the New York Times, “Flame retardant materials inside the plane, including foil wrapping under the seats, most likely helped protect many passengers.”
Categories of Flame Retardants
Materials and products that need to be fire-resistant can be chemically and physically different, and have different uses requiring the need for a variety of flame retardants.
Chlorine and bromine are examples of halogenated flame retardants.
Halogenated flame retardants have one carbon atom bound to a halogen atom and are used to protect many types of plastics and textiles.
Tetrabromobisphenol-A (TBBPA) is a halogenated flame retardant used as a raw material to manufacture printed circuit boards.
It is also used in the plastic casings that surround electrical and electronic components.
Phosphorus is used to produce liquid and solid organic or inorganic flame retardants.
These types of flame retardants are extensively used in polyurethane foams to make fire resistant furniture, mattresses, and thermal insulation materials.
Phosphorous is commonly used in fire resistant coatings and flexible polyvinyl chloride (PVC).
It is also applied in electronics and in high temperature plastics used for manufacturing switches and connectors, and it is used for casings in some less flammable plastics.
Nitrogen-based flame retardants are used in nylons, polyolefins, polyurethane foams, and fire-resistant paints, textiles and wallpapers.
Various inorganic and mineral compounds are combined with bromine, phosphorus or nitrogen and used as flame retardants or as elements of flame retardant systems.
The inorganic compounds include those based on nitrogen, graphite, silica, and inorganic phosphates such as ammonium phosphate and polyphosphate.
Mineral compounds include certain phosphates, metal oxides, hydroxides, and other metal products such as aluminum, zinc and magnesium.
Inorganic and mineral compounds used with other elements can help to achieve fire safety in plastics, foams, textiles and wood products.
The term flame retardants subsumes a diverse group of chemicals which are added to manufactured materials, such as plastics and textiles, and surface finishes and coatings.
Flame retardants are activated by the presence of an ignition source and are intended to prevent or slow the further development of ignition by a variety of different physical and chemical methods. They may be added as a copolymer during the polymerisation process, or later added to the polymer at a moulding or extrusion process or (particularly for textiles) applied as a topical finish.
Mineral flame retardants are typically additive while organohalogen and organophosphorus compounds can be either reactive or additive.
Classes
Both Reactive and Additive Flame retardants types, can be further separated into several different classes:
Minerals such as aluminium hydroxide (ATH), magnesium hydroxide (MDH), huntite and hydromagnesite, various hydrates, red phosphorus, and boron compounds, mostly borates.
Organohalogen compounds.
This class includes organochlorines such as chlorendic acid derivatives and chlorinated paraffins;
organobromines such as decabromodiphenyl ether (decaBDE), decabromodiphenyl ethane (a replacement for decaBDE), polymeric brominated compounds such as brominated polystyrenes, brominated carbonate oligomers (BCOs), brominated epoxy oligomers (BEOs), tetrabromophthalic anyhydride, tetrabromobisphenol A (TBBPA) and hexabromocyclododecane (HBCD).
Most but not all halogenated flame retardants are used in conjunction with a synergist to enhance their efficiency.
Antimony trioxide is widely used but other forms of antimony such as the pentoxide and sodium antimonate are also used.
Organophosphorus compounds.
This class includes organophosphates such as triphenyl phosphate (TPP), resorcinol bis(diphenylphosphate) (RDP), bisphenol A diphenyl phosphate (BADP), and tricresyl phosphate (TCP); phosphonates such as dimethyl methylphosphonate (DMMP); and phosphinates such as aluminium diethyl phosphinate.
In one important class of flame retardants, compounds contain both phosphorus and a halogen. Such compounds include tris(2,3-dibromopropyl) phosphate (brominated tris) and chlorinated organophosphates such as tris(1,3-dichloro-2-propyl)phosphate (chlorinated tris or TDCPP) and tetrakis(2-chlorethyl)dichloroisopentyldiphosphate (V6).[7]
Organic compounds such as carboxylic acid[9] and dicarboxylic acid
The mineral flame retardants mainly act as additive flame retardants and do not become chemically attached to the surrounding system. Most of the organohalogen and organophosphate compounds also do not react permanently to attach themselves into their surroundings but further work is now underway to graft further chemical groups onto these materials to enable them to become integrated without losing their retardant efficiency.
This also will make these materials non emissive into the environment.
Certain new non halogenated products, with these reactive and non emissive characteristics have been coming onto the market since 2010, because of the public debate about flame retardant emissions. Some of these new Reactive materials have even received US-EPA approval for their low environmental impacts.
Retardation mechanisms
The basic mechanisms of flame retardancy vary depending on the specific flame retardant and the substrate.
Additive and reactive flame-retardant chemicals can both function in the vapor (gaseous) or condensed (solid) phase.
Endothermic degradation
Some compounds break down endothermically when subjected to high temperatures. Magnesium and aluminium hydroxides are an example, together with various carbonates and hydrates such as mixtures of huntite and hydromagnesite.
The reaction removes heat from the substrate, thereby cooling the material.
The use of hydroxides and hydrates is limited by their relatively low decomposition temperature, which limits the maximum processing temperature of the polymers (typically used in polyolefins for wire and cable applications).
Thermal shielding (solid phase)
A way to stop spreading of the flame over the material is to create a thermal insulation barrier between the burning and unburned parts.
Intumescent additives are often employed; their role is to turn the polymer surface into a char, which separates the flame from the material and slows the heat transfer to the unburned fuel.
Non-halogenated inorganic and organic phosphate flame retardants typically act through this mechanism by generating a polymeric layer of charred phosphoric acid.
Dilution of gas phase
Inert gases (most often carbon dioxide and water) produced by thermal degradation of some materials act as diluents of the combustible gases, lowering their partial pressures and the partial pressure of oxygen, and slowing the reaction rate.
Gas phase radical quenching
Chlorinated and brominated materials undergo thermal degradation and release hydrogen chloride and hydrogen bromide or, if used in the presence of a synergist like antimony trioxide, antimony halides.
These react with the highly reactive H· and OH· radicals in the flame, resulting in an inactive molecule and a Cl· or Br· radical.
The halogen radical is much less reactive compared to H· or OH·, and therefore has much lower potential to propagate the radical oxidation reactions of combustion.
Use and effectiveness
Fire safety standards
Flame retardants are typically added to industrial and consumer products to meet flammability standards for furniture, textiles, electronics, and building products like insulation.
In 1975, California began implementing Technical Bulletin 117 (TB 117), which requires that materials such as polyurethane foam used to fill furniture be able to withstand a small open flame, equivalent to a candle, for at least 12 seconds.
In polyurethane foam, furniture manufacturers typically meet TB 117 with additive halogenated organic flame retardants.
Although no other U.S. states have a similar standard, because California has such a large market many manufacturers meet TB 117 in products that they distribute across the United States.
The proliferation of flame retardants, and especially halogenated organic flame retardants, in furniture across the United States is strongly linked to TB 117.
In response to concerns about the health impacts of flame retardants in upholstered furniture, in February 2013 California proposed modifying TB 117 to require that fabric covering upholstered furniture meet a smolder test and to eliminate the foam flammability standards.
Gov. Jerry Brown signed the modified TB117-2013 in November and it became effective in 2014.
The modified regulation does not mandate a reduction in flame retardants.
However, these questions of eliminating emissions into the environment from flame retardants can be solved by using a new classification of highly efficient flame retardants, which do not contain halogen compounds, and which can also be keyed permanently into the chemical structure of the foams used in the furniture and bedding industries.
The resulting foams have been certified to produce no flame retardant emissions.
This new technology is based on entirely newly developed “Green Chemistry” with the final foam containing about one third by weight of natural oils. Use of this technology in the production of California TB 117 foams, would allow continued protection for the consumer against open flame ignition whilst providing the newly recognized and newly needed protection, against chemical emissions into home and office environments.
More recent work during 2014 with this “Green Chemistry” has shown that foams containing about fifty percent of natural oils can be made which produce far less smoke when involved in fire situations. The ability of these low emission foams to reduce smoke emissions by up to 80% is an interesting property which will aid escape from fire situations and also lessen the risks for first responders i.e. emergency services in general and fire department personnel in particular.
In Europe, flame retardant standards for furnishings vary, and are their most stringent in the UK and Ireland.
Generally the ranking of the various common flame retardant tests worldwide for furniture and soft furnishings would indicate that the California test Cal TB117 – 2013 test is the most straightforward to pass, there is increasing difficulty in passing Cal TB117 -1975 followed by the British test BS 5852 and followed by Cal TB133. One of the most demanding flammability tests worldwide is probably the US Federal Aviation Authority test for aircraft seating which involves the use of a kerosene burner which blasts flame at the test piece. The 2009 Greenstreet Berman study, carried out by the UK government, showed that in the period between 2002 and 2007 the UK Furniture and Furnishings Fire Safety Regulations accounted for 54 fewer deaths per year, 780 fewer non-fatal casualties per year and 1065 fewer fires each year following the introduction of the UK furniture safety regulations in 1988.[17]
Effectiveness
The effectiveness of flame retardant chemicals at reducing the flammability of consumer products in house fires is disputed.
Advocates for the flame retardant industry, such as the American Chemistry Council’s North American Flame Retardant Alliance, cite a study from the National Bureau of Standards indicating that a room filled with flame-retarded products (a polyurethane foam-padded chair and several other objects, including cabinetry and electronics) offered a 15-fold greater time window for occupants to escape the room than a similar room free of flame retardants.
However, critics of this position, including the lead study author, argue that the levels of flame retardant used in the 1988 study, while found commercially, are much higher than the levels required by TB 117 and used broadly in the United States in upholstered furniture.[10]
Another study concluded flame retardants are an effective tool to reduce fire risks without creating toxic emissions.
Several studies in the 1980s tested ignition in whole pieces of furniture with different upholstery and filling types, including different flame retardant formulations.
In particular, they looked at maximum heat release and time to maximum heat release, two key indicators of fire danger.
These studies found that the type of fabric covering had a large influence on ease of ignition, that cotton fillings were much less flammable than polyurethane foam fillings, and that an interliner material substantially reduced the ease of ignition.[21][22] They also found that although some flame retardant formulations decreased the ease of ignition, the most basic formulation that met TB 117 had very little effect.[22] In one of the studies, foam fillings that met TB 117 had equivalent ignition times as the same foam fillings without flame retardants.[21] A report from the Proceedings of the Polyurethane Foam Association also showed no benefit in open-flame and cigarette tests with foam cushions treated with flame retardants to meet TB 117.
However, other scientists support this open-flame test.
Compared with cotton, flame retardants increase fire toxicity.
They have a large effect on bench-scale flammability tests, but a negligible effect on large scale fire tests.
Furniture of naturally flame-retardant materials is much safer than foam with fire retardants.
Environmental and health issues
The environmental behaviour of flame retardants has been studied since the 1990s.
Mainly brominated flame retardants were found in many environmental compartments and organisms including humans, and some individual substances were found to have toxic properties. Therefore, alternatives have been demanded by authorities, NGOs and equipment manufacturers. The EU-funded collaborative research project ENFIRO (EU research project FP7: 226563, concluded in 2012) started out from the assumption that not enough environmental and health data were known of alternatives to the established brominated flame retardants. In order to make the evaluation fully comprehensive, it was decided to compare also material and fire performance as well as attempt a life cycle assessment of a reference product containing halogen free versus brominated flame retardants. About a dozen halogen free flame retardants were studied representing a large variety of applications, from engineering plastics, printed circuit boards, encapsulants to textile and intumescent coatings. A large group of the studied flame retardants were found to have a good environmental and health profile: ammonium polyphosphate (APP), Aluminium diethyl phosphinate (Alpi), aluminium hydroxide (ATH), magnesium hydroxide (MDH), melamine polyphosphate (MPP), dihydrooxaphosphaphenanthrene (DOPO), zinc stannate (ZS) and zinc hydroxstannate (ZHS). Overall, they were found to have a much lower tendency to bioaccumulate in fatty tissue than the studied brominated flame retardants.
The tests on the fire behaviour of materials with different flame retardants revealed that halogen free flame retardants produce less smoke and toxic fire emissions, with the exception of the aryl phosphates RDP and BDP in styrenic polymers.
The leaching experiments showed that the nature of the polymer is a dominating factor and that the leaching behaviour of halogen free and brominated flame retardants is comparable.
The more porous or “hydrophilic” a polymers is the more flame retardants can be released.
However, moulded plates which represent real world plastic products showed much lower leaching levels than extruded polymer granules.
The impact assessment studies reconfirmed that the improper waste and recycling treatment of electronic products with brominated flame retardants can produce dioxins which is not the case with halogen free alternatives. Furthermore, the United States Environmental Protection Agency (US-EPA) has been carrying out a series of projects related to the environmental assessment of alternative flame retardants, the “design for environment” projects on flame retardants for printed wiring boards and alternatives to decabromo diphenylethers and hexabromocyclododecane (HBCD).
Mechanisms of toxicity
Direct exposure
Many halogenated flame retardants with aromatic rings, including most brominated flame retardants, are likely thyroid hormone disruptors.
The EPA noted that PBDEs are particularly toxic to the developing brains of animals. Peer-reviewed studies have shown that even a single dose administered to mice during development of the brain can cause permanent changes in behavior, including hyperactivity.
Based on in vitro laboratory studies, several flame retardants, including PBDEs, TBBPA, and BADP, likely also mimic other hormones, including estrogens, progesterone, and androgens.
Bisphenol A compounds with lower degrees of bromination seem to exhibit greater estrogenicity.
Some halogenated flame retardants, including the less-brominated PBDEs, can be direct neurotoxicants in in vitro cell culture studies:
By altering calcium homeostasis and signalling in neurons, as well as neurotransmitter release and uptake at synapses, they interfere with normal neurotransmission.
Mitochondria may be particularly vulnerable to PBDE toxicity due to their influence on oxidative stress and calcium activity in mitochondria.
Exposure to PBDEs can also alter neural cell differentiation and migration during development.
Degradation products
Many flame retardants degrade into compounds that are also toxic, and in some cases the degradation products may be the primary toxic agent:
Halogenated compounds with aromatic rings can degrade into dioxins and dioxin-like compounds, particularly when heated, such as during production, a fire, recycling, or exposure to sun.
Chlorinated dioxins are among the highly toxic compounds listed by the Stockholm Convention on Persistent Organic Pollutants.
Polybrominated diphenyl ethers with higher numbers of bromine atoms, such as decaBDE, are less toxic than PBDEs with lower numbers of bromine atoms, such as pentaBDE.
However, as the higher-order PBDEs degrade biotically or abiotically, bromine atoms are removed, resulting in more toxic PBDE congeners.
When some halogenated flame retardants such as PBDEs are metabolized, they form hydroxylated metabolites that can be more toxic than the parent compound.
These hydroxylated metabolites, for example, may compete more strongly to bind with transthyretin or other components of the thyroid system, can be more potent estrogen mimics than the parent compound, and can more strongly affect neurotransmitter receptor activity.[43][46][47]
Bisphenol-A diphenyl phosphate (BADP) and tetrabromobisphenol A (TBBPA) likely degrade to bisphenol A (BPA), an endocrine disruptor of concern.
Environmental exposure
Flame retardants manufactured for use in consumer products have been released into environments around the world.
The flame retardant industry has developed a voluntary initiative to reduce emissions to the environment (VECAP) by promoting best practices during the manufacturing process.
Communities near electronics factories and disposal facilities, especially areas with little environmental oversight or control, develop high levels of flame retardants in air, soil, water, vegetation, and people.[69][72]
Organophosphorus flame retardants have been detected in wastewater in Spain and Sweden, and some compounds do not appear to be removed thoroughly during water treatment.
Disposal
When products with flame retardants reach the end of their usable life, they are typically recycled, incinerated, or landfilled.
Recycling can contaminate workers and communities near recycling plants, as well as new materials, with halogenated flame retardants and their breakdown products.
Electronic waste, vehicles, and other products are often melted to recycle their metal components, and such heating can generate toxic dioxins and furans.
When wearing Personal Protection Equipment (PPE) and when a ventilation system is installed, exposure of workers to dust can be significantly reduced, as shown in the work conducted by the recycling plant Stena-Technoworld AB in Sweden.[77] Brominated flame retardants may also change the physical properties of plastics, resulting in inferior performance in recycled products and in “downcycling” of the materials. It appears that plastics with brominated flame retardants are mingling with flame-retardant-free plastics in the recycling stream and such downcycling is taking place.[10]
Poor-quality incineration similarly generates and releases high quantities of toxic degradation products.
Controlled incineration of materials with halogenated flame retardants, while costly, substantially reduces release of toxic byproducts.
Many products containing halogenated flame retardants are sent to landfills.
Additive, as opposed to reactive, flame retardants are not chemically bonded to the base material and leach out more easily.
Brominated flame retardants, including PBDEs, have been observed leaching out of landfills in industrial countries, including Canada and South Africa.
Some landfill designs allow for leachate capture, which would need to be treated. These designs also degrade with time.
Regulatory opposition
Shortly after California amended TB117 in 2013 to require only flame-resistant furniture coverings (without restriction on the interior components), furniture manufacturers across the US heard increased demands for flame-retardant-free furniture. Of note, smolder-resistant fabrics used in flame-resistant coverings do not contain PBDEs, organophosphates, or other chemicals historically associated with adverse effects on human health.
A number of decision-makers in the health sector – which accounts for nearly 18% of the US GDP [76] – are committed to purchasing such materials and furniture.
Early adopters of this policy included Kaiser Permanente, Advocate Health Care, Hackensack University Hospital, and University Hospitals.
All together, furniture purchasing power of these hospitals totalled $50 million.
All of these hospitals and hospital systems ascribe to the Healthier Hospitals Initiative, which has over 1300 member hospitals, and promotes environmental sustainability and community health within the healthcare industry.
Further legislation in California has served to educate the public about flame retardants in their homes, in effect reducing consumer demand for products containing these chemicals. According to a law (Senate Bill, 1019) signed by Governor Jerry Brown in 2014, all furniture manufactured after January 1, 2015 must contain a consumer warning label stating whether it does or does not contain flame retardant chemicals.
As of September 2017, the topic reached federal regulatory attention in the Consumer Product Safety Commission, which voted to put together a Chronic Hazard Advisory Panel focused on describing certain risks of various consumer products, specifically baby and childcare products (including bedding and toys), upholstered home furniture, mattresses and mattresses and mattress pads, and plastic casings surrounding electronics. This advisory panel is charged specifically to address the risks of additive, non-polymeric organohalogen flame retardants (OFRs).
Although these chemicals have not been banned, this ruling sets in motion an in-depth consumer safety investigation which could eventually lead to complete removal of these substances from consumer manufacturing.[79]
Pursuant with the Toxic Substances Control Act of 1976, the Environmental Protection Agency is also actively evaluating the safety of various flame retardants, including chlorinated phosphate esters, tetrabromobisphenol A, cyclic aliphatic bromides, and brominated phthalates.
Further regulations depend on EPA findings from this analysis, though any regulatory processes could take several years.
National Bureau of Standards testing
In a 1988 test program, conducted by the former National Bureau of Standards (NBS), now the National Institute of Standards and Technology (NIST), to quantify the effects of fire retardant chemicals on total fire hazard.
Five different types of products, each made from a different type of plastic were used.
The products were made up in analogous fire-retardant (FR) and non-retarded variants (NFR).
The impact of FR (flame retardant) materials on the survivability of the building occupants was assessed in two ways:
First, comparing the time until a domestic space is not fit for occupation in the burning room, known as “untenability”; this is applicable to the occupants of the burning room. Second, comparing the total production of heat, toxic gases, and smoke from the fire; this is applicable to occupants of the building remote from the room of fire origin.[81]
The time to untenability is judged by the time that is available to the occupants before either
(a) room flashover occurs, or
(b) untenability due to toxic gas production occurs.
For the FR tests, the average available escape time was more than 15-fold greater than for the occupants of the room without fire retardants.
Hence, with regard to the production of combustion products,
The amount of material consumed in the fire for the fire retardant (FR) tests was less than half the amount lost in the non-fire retardant (NFR) tests.
The FR tests indicated an amount of heat released from the fire which was 1/4 that released by the NFR tests.
The total quantities of toxic gases produced in the room fire tests, expressed in “CO equivalents,” were 1/3 for the FR products, compared to the NFR ones.
The production of smoke was not significantly different between the room fire tests using NFR products and those with FR products.
Thus, in these tests, the fire retardant additives decreased the overall fire hazard.
Global demand
In 2013, the world consumption of flame retardants was more than 2 million tonnes.
The commercially most import application area is the construction sector.
It needs flame retardants for instance for pipes and cables made of plastics.
In 2008 the United States, Europe and Asia consumed 1.8 million tonnes, worth US$4.20-4.25 billion.
According to Ceresana, the market for flame retardants is increasing due to rising safety standards worldwide and the increased use of flame retardants.
It is expected that the global flame retardant market will generate US$5.8 billion.
In 2010, Asia-Pacific was the largest market for flame retardants, accounting for approximately 41% of global demand, followed by North America, and Western Europe
Flame retardants are chemicals that are applied to materials to prevent the start or slow the growth of fire.
They have been used in many consumer and industrial products since the 1970s, to decrease the ability of materials to ignite.
Flame retardants are often added or applied to the following products.
Furnishings, such as foam, upholstery, mattresses, carpets, curtains, and fabric blinds.
Electronics and electrical devices, such as computers, laptops, phones, televisions, and household appliances, plus wires and cables.
Building and construction materials, including electrical wires and cables, and insulation materials, such as polystyrene and polyurethane insulation foams.
Transportation products, such as seats, seat covers and fillings, bumpers, overhead compartments, and other parts of automobiles, airplanes, and trains.
Many flame retardants have been removed from the market or are no longer produced. However, because they do not easily break down, they can remain persistent in the environment for years. They can also bioaccumulate, or build up in people and animals over time.
Are there different types of flame retardants?
There are hundreds of different flame retardants. They are often broken into categories based on chemical structure and properties.
In general, flame retardants are grouped based on whether they contain bromine, chlorine, phosphorus, nitrogen, metals, or boron.
Brominated flame retardants — Contain bromine and are the most abundantly used flame retardants.
Used in many consumer goods, including electronics, furniture, building materials, etc. and have been linked to endocrine disruption among other effects.
Polybrominated diphenyl ethers (PBDE’s) —PBDEs do not chemically bind with the products to which they are added (furniture, electronics, etc.) so they easily release from these products and enter air and dust. PBDEs can lower birth weight/length of children, and impair neurological development.
Tetrabromobisphenol A (TBBPA) — Widely used to make computer circuit boards and electronics.
Also used in some textiles and paper, or as an additive in other flame retardants.
Hexabromocyclododecane (HBCD) — An additive primarily used in polystyrene foam building materials.
The primary risk to humans is from leaching out of products and getting into indoor dust. Low levels of HBCD have also been found in some food products.
Organophosphate flame retardants (OPFRs) — With the phasing out of PBDEs, some OPFRs have been identified as replacements.
NIEHS-supported researchers are also looking at the health effects of newer flame retardant alternatives that are being brought to market.
Flame retardants are chemicals that are added to manufactured materials (e.g., textiles and plastics) and surface finishes and coatings to inhibit combustion or delay the spread of fire after ignition (van der Veen and de Boer, 2012)
Halogenated flame retardants have been a serious concern to health and environmental scientists
Flame retardant chemicals are used in commercial and consumer products (such as furniture and building insulation) to meet flammability standards.
Not all flame retardants present concerns, but the following types often do:
(1) halogenated flame retardants, also known as organo-halogen flame retardants that contain chlorine or bromine bonded to carbon and
(2) organo-phosphorous flame retardants that contain phosphorous bonded to carbon.
Flame retardants inhibit or delay the spread of fire by suppressing the chemical reactions in the flame or by the formation of a protective layer on the surface of a material.
They may be mixed with the base material (additive flame retardants) or chemically bonded to it (reactive flame retardants).
Mineral flame retardants are typically additive, while organohalogen and organophosphorus compounds can be either reactive or additive.
Many flame retardants, while having measurable or considerable toxicity, degrade into compounds that are also toxic, and in some cases, the degradation products may be the primary toxic agent. For example, halogenated compounds with aromatic rings can degrade into dioxin derivatives, particularly when heated, such as during production, a fire, recycling, or exposure to sun. In addition, polybrominated diphenyl ethers with higher numbers of bromine atoms, such as decabromodiphenyl ether (decaBDE), are less toxic than pentabromodiphenyl ether derivatives with lower numbers of bromine atoms (Table 4.4). However, as the higher-order pentabromodiphenyl ether derivatives degrade biotically or abiotically, bromine atoms are removed, resulting in more toxic pentabromodiphenyl ether derivatives.
In addition, when some of the halogenated flame retardants such as pentabromodiphenyl ether derivatives are metabolized, they form hydroxylated metabolites that can be more toxic than the parent compound. These hydroxylated metabolites, for example, may compete more strongly to bind with transthyretin or other components of the thyroid system, can be more potent estrogen mimics than the parent compound, and can more strongly affect neurotransmitter receptor activity.
When products with flame retardants reach the end of their usable life, they are typically recycled, incinerated, or landfilled.
Recycling can contaminate workers and communities near recycling plants, as well as new materials, with halogenated flame retardants and their breakdown products. Electronic waste, vehicles, and other products are often melted to recycle their metal components, and such heating can generate toxic dioxins and furans.
Brominated flame retardants may also change the physical properties of plastics, resulting in inferior performance in recycled products.
Poor-quality incineration similarly generates and releases high quantities of toxic degradation products.
Controlled incineration of materials with halogenated flame retardants, while costly, substantially reduces release of toxic by-products.
Many products containing halogenated flame retardants are sent to landfills.
Additive, as opposed to reactive, flame retardants are not chemically bonded to the base material and leach out more easily.
Brominated flame retardants, including pentabromodiphenyl ether derivatives, have been observed leaching out of landfills in some countries.
Landfill designs must allow for leachate capture, which would need to be treated, but these designs can degrade with time.
Flame retardants are chemicals which are added to many materials to increase their fire safety.
For example, many plastics are highly flammable and therefore their fire resistance is increased by adding flame retardants in order to reduce the risk of fire.
Flame retardants are chemicals that are added to flammable materials—such as wood, plastic, paper, rubber, or fibers—to make them less likely to catch fire or to prevent the spread of fire.
Some materials used in buildings, household goods, daily necessities, and electronics such as household appliances, can be sources of fires or lead to fire spreading.
If we are to live safe and healthy lives, we need to make these materials less flammable and reduce the generation of toxic gases or substances.
“Flame retardant” is the generic name for chemicals used to meet these goals and requirements.
Types of flame retardants
Organic flame retardants
Bromine compounds
Chlorine compounds
Phosphorous compounds, etc.
Inorganic flame retardants
Antimony compounds
Metal hydroxides
Nitrogen compounds
Boron compounds, etc.
Flame retardants are sometimes referred to as additive flame retardants or reactive flame retardants, depending on their function.
Flame-retardant mechanisms
Creation of an oxygen-isolating layer.
Supplementation and stabilization of generated active radicals and suppression of combustible gas generation.
Removal of heat away from combustibles (endothermic reactions).
Carbonization of burning portions to immobilize them and isolate heat and oxygen.
Generation of inactive gases and dilution of combustible gases.
Published September 2020
Flame retardants are materials or chemicals that are used to deter or extinguish flame propagation in resins, elastomers, textiles, coatings, adhesives, and sealants.
The most important product categories are brominated compounds, organophosphorus compounds, chlorinated compounds, aluminum trihydroxide, antimony oxide, boron compounds, magnesium hydroxide, and “other” flame retardant products. In 2019, the most important flame retardant product types by volume were aluminum trihydroxide, with 38% of the total market, followed by organophosphorus compounds (18%), brominated compounds (17%), and antimony oxides (9%). The product mix varies widely by region.
The flame retardant industry is highly affected by regional regulations and standards (and differences) for construction and electrical/electronic applications.
An increase in high-rise fires around the world has shown the need for improved safety standards for aluminum composite panel cladding used in building siding (or a method for upgrading older building materials [with older standards] to newer standards) using flame retardants for improved safety. Some flame retardants, especially brominated flame retardants, have restricted production and consumption. For example, hexabromocyclododecane (HBCD), is no longer allowed to be used in Japan (2014), the European Union (2015), and Canada (year-end 2016).
Flame retardants play an important role in fire prevention and suppression. Strict fire safety standards reduce the detrimental impact of fires on people, property, and the environment.
Flame retardants not only prevent fires from starting, but if a fire does occur, they slow down the spread of the fire and enhance the opportunity time for safe escape.
They can mean the difference between life and death.
lame retardants are substances or compounds that are added to other materials, such as plastics, coatings and textiles to prevent or delat the the spread of fire.
The first applications of flame retardants predate the Gregorian calendar.
Egyptians soaked wood in alum (potassium aluminium sulphate) around 450 B.C. and timbers were painted with vinegar arounsd 360 B.C. to increase their resistance to fire.
Since then, many other materials have been used as flame retardants including clay, hair and gypsum.
In 1735, Obadiah Wilde received British patent 551 for his mixture of alum, borax (sodium borate) and ferrous sulphate, which he used to improve the flame retardancy of paper and textile.
His invention was first applied to improve safety of canvas used in theatres and public buildings.
Today, global demand for flame retardants has exceeded 2 million tons per year. A major part of this demand comes from the global plastic industries.
Since all carbon-based materials are combustible, and the use of plastics is so widespread, there is a need to decrease the risk of fire related accidents.
If it is not possible to select a polymer that is inherently flame retardant (e.g. polyamide), adding a flame retardant is a solution.
The flame retardant can be mixed with the base material or chemically bonded to it. Broadly speaking, flame retardants can be devided in three groups,
(1) inorganic or mineral flame retardants and
(2) halogenated compounds. While the performance of halogenated flame retardance is excellent, many of these chemicals are associated with health and environmental problems.
As a result, several brominated and chlorinated flame retardants have been banned in the past.
Examples of banned compounds include polychlorinated biphenyls (PCBs), polybrominated diphenyl ethers (PBDEs) and Decabromodiphenyl ether (DecaBDE).
Companies looking for less toxic products, often try to make changes to the articles materials and design or to select safer (inorganic) chemicals.
Examples of such chemicals include aluminium trihydroxide (ATH), a mixture of huntitite and hydromagnesite and magnesium (di)hydroxide (MDH).
These mineral flame retardants are non-toxic and work by decomposing endothermically.
This means that at a certain temperature, the compounds fall apart thereby adsorbing heat and releasing water vapor.
The oxides that are formed results in a protective layer that provides a smoke suppressing effect.
Despite the obvious advantages of mineral flame retardants, it is not always possible to replace halogenated flame retadants.
To reach flammability standards in demanding applications, mineral flame retardants need to be added in very high dosage levels (up to 80 w/w%).
One of the principal classes of flame retardants used for plastics textiles, paper andwood is that of phosphorus, phosphorus-nitrogen, and phosphorus-halogen compounds, representing over one third of the overall market revenue from flame retardants and with the highest growth.
Commercial phosphorus-based flame retardants include some inorganic compounds as well as both additive and reactive organic phosphorus systems.
These materials range from simple salts to oligomeric compounds and encompass both liquids and solids
Reviews of this topic are found in the general references already cited, and more details are given for a number of the individual compounds discussed in this article.
Phosphorus flame retardants have a multiplicity of modes of action, both condensed and vapor phase, which we will briefly survey.
Some phosphorus-based flame retardants havebeen shown to have both vapor-phase and condensed-phase modes of action.
The science is in an evolving state with many unresolved questions
Insoluble Ammonium PolyphosphateWhen ammonium phosphates are heated by themselves under ammonia pressure or preferably in the presence of urea, relatively water-insoluble ammonium polyphosphate [68333-79-9] is produced.
There are two crystal forms, depending on heating conditions. Form I, sold as ICL’s Phoschek P30 and used mostly in coatings is lower molecular weight linear, with onset of weight loss ~240°C and relatively more water soluble. Form II, sold as Clariant’s Exolit AP422 and by several other European and Asian manufacturers, is higher molecular weight, probably cross-linked, with onset of weight loss ~270°C, and much more water-resistant.
Commercial products, available from a number of manufacturers, are available with a variety of particle sizes and surface coatings or encapsulants such as melamine–formaldehyde or other thermoset resins to impede hydrolysis.These finely divided solids are principal ingredients of intumescent flame retardant paints and mastics.
In such formulations, ammonium polyphosphate is considered to function as a catalyst.
Thus when the intumescent coating is exposed to a high temperature, the ammonium polyphosphate yields a phosphorus acid that then interacts with an organic component such as a pentaerythritol to form a carbonaceous char. The chemistry has been described in detail.
A blowing (gas-generating) agent, such as melamine or chlorowax, is also present to impart a foamed character to the char, thus forming a fire-resistant insulating barrier to protect the substrate.
In addition, the intumescent formulations typically contain resinous binders, pigments, and other fillers.
Mastics are related but generally more viscous formulations, intended to be applied in thick layers to girders, trusses, and decking; these generally contain mineral fibers to increase coherence.
Besides the well-established coating applications, many studies have been done and some commercialization has resulted with intumescent formulations for thermoplastics, in particular for polyolefins, ethylene–vinyl acetate, and urethane elastomers.
The char-forming resin can be, an ethyleneurea–formaldehyde condensation polymer, a hydroxyethyl isocyanurate, or a piperazine–triazine resin.
In noncharrable polymers such as polypropylene, blending of charrable polymers such as thermoplastic polyurethanes can make ammonium polyphosphate perform as a flame retardant.
Recently developed triazine-piperazine-morpholine products offer enhanced char formation with ammonium polyphosphate in polyolefins.
Ammonium polyphosphate also finds use as a flame retardant in rigid polyurethane foams
Flame retardants refer to a variety of chemical compounds added to otherwise combustible materials to create a layer of flammability protection, providing more time to escape and for first responders to save lives and minimize property damage.
Because the need to reduce the risk of fire is critical for many paper and textile applications, flame retardants are prevalent in products ranging from home furnishings (upholstered furniture, curtains, mattresses, etc.) to transportation (fabric seating, air and liquid filtration, and other components) to building and construction materials (carpeting and walls) and more.
Each application has its own inherent flame retardant needs, presenting unique challenges to formulators.