AskDefine | Define intumescent

User Contributed Dictionary



  1. That becomes swollen, especially upon exposure to heat

Related terms

Extensive Definition

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

Types of intumescents

Soft char producers

These intumescents produce a light char, which is a poor conductor of heat, thus retarding heat transfer. Typically, these materials also 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, it is only the insulation characteristics of the char that was produced, which 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 of structural steel as well as 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 expanding char producers

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, with a quantifiable expansion pressure. In the case of the firestops, a melting, burning plastic pipe must be squeezed together and shut so that there will be no hole for fire to go through an opening in an otherwise fire-resistance rated wall or floor assembly. In the case of the 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 not typically used for interior spray fireproofing as they are not suitable for that application.

Uses of intumescents in passive fire protection



Problems with intumescents

Some intumescents are susceptible to environmental influences such as humidity, which can reduce or negate their ability to function. DIBt approvals quantify 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.


: This product is suitable for use in passive fire protection in general, firestopping and interior fireproofing in particular. The small, orange chunk on the bottom right hand side is capable of growing into that large black shape. This type of intumescent is typically highly endothermic. It contains a lot of chemically bound water, in hydrates. As this is released, it cools adjacent materials. Such intumescents are useful as ingredients in firestop pillows and in paints, which are used for fireproofing purposes. These intumescents do not produce enough expansion force to be used in plastic pipe devices, where the intumescent must squeeze a melting plastic pipe or conduit shut.
listing and approval use and compliance of the installed configuration.
passive fire protection example of an intumescent with strong expansion pressure. This intumescent is called Palusol. It is based on waterproofed sodium silicate. Another high-expansion intumescent popular for use in plastic pipe firestop devices is graphite. Graphite tends to be less affected by atmospheric conditions than many water-bearing intumescents.


See also

External links

intumescent in German: Intumeszenz
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