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, in America, 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.