Fire is a destructive force affecting lives, economies and environments in many ways. Globally, estimated fire deaths for 2015 were over 18,000. While this figure is alarming, it is the result of a downward trend from a high estimate of over 62,000 in 2002.1 In the US, demand for fire retardant coatings grew an average of 6 percent annually between 2012 and 2016 to reach $1.6 billion.
The definition of a fire retardant coating is not clear-cut and often confused or interchanged with the term “fire-resistant,” but there is a distinction. A fire-resistant coating doesn’t ignite or support flame when an ignition source is applied, while a fire retardant coating protects the substrate from burning. In performance-based testing, the mechanism of protection is secondary to the final result.
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End uses for fire resistant coatings
Fire retardant coatings are largely used in two important parts of everyday life: occupancy and mobility. By this I mean, fire retardant coatings are most used within the built environments we occupy or the modes of transportation we use to move between them. The three most important application areas for fire retardant coatings are:
- Building products: structural steel, interior and exterior cladding (wood, composite)
- Aircraft: interior/exterior (metal or composite) (wood – executive aircraft interiors)
- Public transportation: interior/exterior (metal or composite)
Certification of fire retardant coatings
Many applications of fire retardant coatings require certification that the material provides the proper degree and manner of fire protection appropriate for the end use. Different organizations test and certify fire retardant coatings. These organizations include but are not limited to the following:
Governmental regulators
- Federal Aviation Administration (FAA)
- Interior/exterior aircraft components
- Transport Canada
- Interior rail components
Trade associations/Non-government organizations (NGO)
- National Fire Protection Association (NFPA)
- Guidelines for commercial and residential construction
- American Society for Testing of Materials (ASTM)
- Broad range of test methods for various end uses
Corporate standards
- Boeing
- Airbus
Key performance indicators and testing
Fire resistance is typically evaluated by impinging an ignition source on a test sample under controlled conditions and measuring one or more of the following performance parameters.
- Flame Spread measures the extent of the burned surface from the original site of ignition.
- Self-Extinguishing is defined as the ability to extinguish a flame after the ignition source is removed from contact with the test sample.
- Smoke Density is an indicator of the optical density of the smoke generated from the burning test sample.
- Smoke Toxicity requires specific chemical analysis for targeted toxic components in the smoke generated during combustion.
- Heat Release uses calorimetry to determine peak and average energy produced by combustion of the test sample.
Materials utilized to achieve fire retardancy
Several factors determine which fire retardant material or combination of materials to use. Regulations such as REACH and RoHS can eliminate non-conforming materials regardless of any performance or economic advantages and should be the first screening stage gate. For example, RoHS regulations prohibit the use of several brominated organic compounds which were once commonly used as fire retardants.
The intended application and required performance benchmarks are the next screening criteria, not only from the perspective of what fire retardant materials to use but also how fire retardants can affect other physical properties of the coating in its end use. Fire retardant materials act through one or more mechanisms to reduce flame propagation in coatings. These mechanisms act on the sides of the fire tetrahedron2 to interrupt the rapid oxidation reaction at the base.
- Compounds that generate free radicals interfere with the oxidation/reduction reaction, driving combustion and reducing the rate of burning until fire is unsustainable.
- Intumescent agents increase in volume and create an non-flammable char layer which insulates and prevents oxygen from reaching the substrate.
- Fire retardants which absorb the heat of combustion when undergoing dehydration or endothermic decomposition reactions act by cooling the flames below the ignition temperature.
Halogenated compounds
- Generate free radicals which inhibit oxidation in the gas/vapor phase of the combustion reaction
- Produce corrosive and toxic smoke
- Are cost-effective
- Are easy to incorporate and process
- Halogenated fire retardants
- Brominated
- Chlorinated
Halogen-free compounds
- Act through various mechanisms
- Generate smoke that is much less toxic than that generated by halogenated compounds
- Cost more than halogenated compounds
- Could benefit from processing and incorporation improvements
- Halogen-free fire retardant examples
- Metal hydroxides – endothermic dehydration, char formation
- Phosphorous-based – char formation
- Melamine-based – endothermic decomposition, synergistic effects with phosphorus compounds
Summary
Choosing specific fire retardant chemistries not only depends on the targeted performance objectives but also on regulations which may prohibit certain compounds. The most effective fire retardant coatings often rely on a combination of compounds; synergy within that combination plays an important role in the efficacy of the final product.
Further reading
- Take Flight with Exterior Aerospace Coatings
- A Solid Approach to Lower VOCs
- Passing the Test: New Coatings Require New Equipment and Testing
References:
- International Association of Fire and Rescue Services (CTIF): World Fire Statistics 2017 [PDF]
- Wikipedia: Fire tetrahedron
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Wally,
That was a nice, informative article on the very hot topic of fire retardant coatings. Keep up the good work!
Mark H.
WE ARE MANUFACTURER OF INDUSTRIAL PAINTS USED IN AUTOMOTIVE COMPONENTS AND HEAVY EQUIPMENT INDUSTRIES.
WE HAVE DEVELOP NEAR INFRRED REFLECTIVE PAINTS FOR APPLICATIONS IN DEFENCE.
PLEASE SHARE MORE INFORMATION REGARDING MEDIUM TO BE USED FOR EXTERIOR APPLICATIONS.ALSO THE PIGMENTS,BINDER SYSTEM SHOULD COMPLY WITH THE IR REFLECTIVE PARAMETERS.
We are one of the leading paint and resin manufacturers in the center of China.
We have developed RTV Silicone Rubber Coating applied on insulator in STATE GRID.
We d like to know if you can supply us low VOC RTV Silicone Rubber Coating applied on insulator ?
Any ICE-prevention coating on insulator solution?
Hi Joy,
We are not suppliers of any materials. You can search a wide variety of materials and contact suppliers via UL Prospector: https://www.ulprospector.com/en/na/Coatings
Thanks!
Angie
Content Manager, UL Prospector Knowledge Center
Interesting article on fire retarding coatings for building structures. We have a big scope of implementing & adopting fire retarding coatings for all building structures in india.
We are manufacturer of specialty coatings for wood , plastics & metals for industrial applications in india.
Excellent Content! Very well explained that synergy within the combination plays an important role in the efficacy of the final product. This was very informative! Keep Posting!