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Title: Intumescent  
Author: World Heritage Encyclopedia
Language: English
Subject: Firestop pillow, Sodium silicate, Putty, Fire test, Plaster
Collection: Firestops, Materials
Publisher: World Heritage Encyclopedia


An intumescent is a substance that swells as a result of heat exposure, thus increasing in volume and decreasing in density. Intumescents are typically used in passive fire protection and, in the U.S., require listing and approval use and compliance in their installed configurations in order to comply with the law.


  • Types 1
    • Soft char 1.1
    • Hard char 1.2
  • Applications 2
  • Problems 3
  • Gallery 4
  • See also 5
  • References 6
  • External links 7


Soft char

These intumescents produce a light char, which is a poor conductor of heat, thus retarding heat transfer. Typically, these materials contain a significant amount of hydrates. As the hydrates are spent, water vapour is released, which has a cooling effect. Once the water is spent, the insulation characteristics of the char that remains can slow down heat transfer from the exposed side to the unexposed side of an assembly. Soft char producers are typically used in thin film intumescents for fireproofing structural steel as well as in firestop pillows. Typically, the expansion pressure that is created for these products is very low, because the soft carbonaceous char has little substance, which is beneficial if the aim is to produce a layer of insulation.

Hard char

Harder chars are produced with sodium silicates and graphite. These products are suitable for use in plastic pipe firestops as well as exterior steel fireproofing. In those applications, it is necessary to produce a more substantial char capable of exerting quantifiable expansion pressure. In the case of firestops, a melting, burning plastic pipe must be squeezed together and shut so that there will be no opening for fire to propagate to an otherwise fire-resistance rated wall or floor assembly. In the case of exterior fireproofing, a hydrocarbon fire must be held off with quite potentially more kinetic energy than a house fire. Intumescents that produce hard chars are unsuitable for interior spray fireproofing.


Intumescents are used to achieve passive fire protection for such applications as firestopping, fireproofing, gasketing and window casings. Such applications are relevant for buildings, offshore constructions, ships and aircraft.


Some intumescents are susceptible to environmental influences, such as humidity, which can reduce or negate their ability to function. In Germany, the Deutsches Institut für Bautechnik, DIBt,[1] quantifies the ability of intumescents to stand the test of time against various environmental exposures. DIBt-approved firestops and fireproofing materials are available in Canada and the U.S.


See also


  1. ^ DIBt is a state-level authority concerned with technical matters related to construction (building regulations, design, testing, certification, safety, building equipment, approvals, etc. See DIBt - Deutsches Institut für Bautechnik)
  2. ^ [2] S-115

External links

  • "The proof is in the fire" Chemical Innovation Magazine, American Chemical Society
  • Article about intumescent materials
  • Translation of DIBt test procedure for intumescent building products
  • Translation of DIBt test procedure for reactive spray fireproofing materials
  • American Chemical Society: Fire Retardancy of Polypropylene Composites Using Intumescent Coatings
  • ASTM E 2786 - 2010 Standard Test Methods for Measuring Expansion of Intumescent Materials Used in Firestop and Joint Systems
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