Fire retardant FRP is not a different material from standard FRP — it is standard polyester or vinyl ester FRP with the resin chemistry modified to resist ignition and slow flame spread. The modification is chemical, not a topical coating. A fire-retardant FRP grating panel has the fire performance built into its matrix, through the full thickness of the material. This distinguishes it from a standard FRP panel that has been painted with a fire-retardant coating, which is a less reliable approach because the coating can be scratched, worn, or chemically degraded.
How Fire Retardancy Is Achieved
Two chemical strategies dominate. The first is the addition of halogenated compounds — typically brominated flame retardants — to the resin. When the resin is heated by a flame, the bromine compounds release bromine radicals that interrupt the combustion reaction in the gas phase, effectively quenching the flame. The second strategy is the addition of alumina trihydrate (ATH), which decomposes endothermically when heated, absorbing heat and releasing water vapor. The water vapor dilutes the combustible gases above the material, and the endothermic decomposition cools the material surface. Both strategies can be used together for synergistic effect. Based on common industrial formulations, fire-retardant additives typically comprise 10–20% of the resin by weight and may modestly influence mechanical properties relative to non-fire-retardant equivalents.
Standards and Test Methods
Fire-retardant FRP is tested and classified under two primary standards in the North American market. ASTM E84 (the Steiner tunnel test) measures flame spread index and smoke developed index along a 7.3 m (24 ft) horizontal sample exposed to a gas flame at one end. A Class 1 (or Class A) rating requires a flame spread index ≤ 25 and a smoke developed index ≤ 450. Most fire-retardant FRP products meet this threshold. For marine applications, the IMO FTP Code (International Maritime Organization Fire Test Procedures Code) applies, and it adds criteria for smoke density and toxicity that go beyond ASTM E84. Phenolic FRP typically meets IMO FTP Code without additional additives because the phenolic chemistry is inherently fire-resistant. Polyester and vinyl ester FRP require fire-retardant additives to meet IMO standards.
Limitations
Fire-retardant FRP is not non-combustible. It will eventually burn if exposed to a sustained, high-intensity flame. The fire-retardant additives slow ignition, reduce flame spread, and limit smoke, but they do not make the material immune to fire. In building code terms, fire-retardant FRP is a "combustible" material with a Class 1 surface burning characteristic — not a "non-combustible" material like concrete, steel, or masonry. Where building codes require non-combustible construction (Type I or Type II), fire-retardant FRP may not be permitted as a structural element without an alternative means-and-methods approval from the authority having jurisdiction. For Type II-B, III, IV, and V construction, Class 1 fire-retardant FRP is generally accepted.
Learn more about fire-rated product options in our Phenolic Grating and FRP Grating specifications.