Intumescent

A charred marshmallow is a familiar example of intumescence

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 protection, where their fire-resistance ratings apply only to the configuration that was tested and listed: standard fire tests such as ASTM E119 and UL 263 rate whole building assemblies such as walls, columns, beams and floors, and any variation from the tested construction, such as its size, method of assembly or materials, may substantially change its performance.

The details for individual building parts are specified in technical standards which are compiled and published by national or international standardization bodies like the British Standards Institute (BSI), the German Institute for Standardization (DIN), the American Society for Testing and Materials (ASTM) or the International Organization for Standardization (ISO).

Intumescent coatings for steel constructions must be approved in standardized fire tests.

Types

Soft char

These intumescent materials produce a light char which is a poor conductor of heat, thus retarding heat transfer. Typically the light char consists of microporous carbonaceous foam formed by a chemical reaction of three main components: ammonium polyphosphate, pentaerythritol, and melamine. The reaction takes place in a matrix formed by the molten binder which is typically based on vinyl acetate copolymers or styrene acrylates.

Ablative coatings contain a significant amount of hydrates. When the hydrates are heated, they decompose, and water vapour is released, which has a cooling effect. Once the water is spent, the insulation characteristics of the char that remains can retard heat transfer through the fire stop assembly.

Soft char products are typically used in thin film intumescent materials for fireproofing protection of structural steel as well as in firestop pillows.

Hard char

Harder char is produced with sodium silicates and graphite. These products are suitable for use in plastic pipe firestops in which applications it is necessary to exert expansion pressure to fill the gap left in the middle of the fire stop assembly left by the melting plastic pipe.

Intumescent coatings

Intumescent coatings may be designed for protection of metals from fire, such as structural steel. They may be based on a number of resin binders including epoxy, and silicone. Melamine-formaldehyde resin systems have been used using layered double-hydroxide modified phosphate esters that improved the intumescent properties.

Problems

Some intumescent materials are susceptible to environmental influences such as humidity, which can reduce or negate their ability to function.[citation needed]

See also

References

  1. ↑ Merriam-Webster Dictionary, intumescence, accessed 13 March 2023
  2. ↑ "UL 263: Fire Tests of Building Construction and Materials" (14th ed.). UL Standards & Engagement. 2 September 2025. Retrieved 26 October 2026.
  3. ↑ "ASTM E119-26: Standard Test Methods for Fire Tests of Building Construction and Materials". ASTM International. 2026. Retrieved 26 October 2026.
  4. ↑ "Fireproofing: 3 Types, Fire Ratings & How to Choose". Construction Chemicals. 2026-10-23. Retrieved 2026-10-26.
  5. ↑ Werle, Peter; Morawietz, Marcus; Lundmark, Stefan; Sörensen, Kent; Karvinen, Esko; Lehtonen, Juha (2008). "Alcohols, Polyhydric". Ullmann's Encyclopedia of Industrial Chemistry. Weinheim: Wiley-VCH. doi:10.1002/14356007.a01_305.pub2. ISBN 978-3527306732.
  6. ↑ Cardoso, de Sa, Beraldo, Hidalgo and Ferreira (November 2020). "Intumescent coatings using epoxy, alkyd, acrylic, silicone and silicone-epoxy hybrid resins for steel fire protection". Journal of Coatings Technology and Research. 17 (6): 1471–1488. doi:10.1007/s11998-020-00366-9. S2CID 220375908.{{cite journal}}: CS1 maint: multiple names: authors list (link)
  7. ↑ Xu, Deng and Lang (January 2020). "Flame retardancy and smoke suppression properties of transparent intumescent fire-retardant coatings reinforced with layered double hydroxides". Journal of Coatings Technology and Research. 17 (1): 157–169. doi:10.1007/s11998-019-00249-8. S2CID 199473315.