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Intumescents are substances which swell as a result of heat exposure thus increasing in volume and decreasing in density. Intumescents are typically used in passive fire protection and require bounding installations in order to comply with the law.
The role of water
Intumescents are typically endothermic * to varying degrees, as they can contain chemically bound water. This can be very important in fire testing. A crucial factor in passing fire tests for passive fire protection products, is to keep the item that is to be protected below its critical temperature. For structural steel, the idea is not to let the steel beam or column get much hotter than ca. 550°C. Steel first expands with increasing heat, but once above its critical temperature, it loses its strength, like spaghetti in boiling water. Hydrates in the intumescent or endothermic coating tend to keep their substrata at 100°C, the boiling point for water, until all the hydrates are spent. In fireproofing applications using waterborne products, the temperature increase in the substrate or the item to be protected, tends to "flatline" at the 100°C mark, until the water is spent. Then, the temperature increase takes off again.
Uses of intumescents in Passive fire protection
Intumescents are used in firestopping, fireproofing and gasketing applications, in buildings, offshore construction, ships, and aircraft.
Unitherm1.jpg|thumb|150px| Pipes covered with a thin-film intumescent spray fireproofing product called Unitherm. As the flame from the blow-torch hits it, the intumescent expands, forming a layer of insulation, which slows down heat transfer to the pipe below. Hydrates within the coating give up their water content, maintaining a temperature near the boiling point of 100°C. The critical steel temperature is ca. 540°C. Once the water is spent and enought heat has gone through the char, the steel can reach and exceed its critical temperature and then lose its strength. The time this takes determines the fire-resistance rating. .]]
Unitherm2.jpg|thumb|150px| See *. In this picture, the flame has been removed after the thin-film intumescent spray fireproofing product has been completely expanded. Some intumescents can undergo shrinkage shortly after full expansion has taken place. The important thing to remember, however, is the need for bounding of the installed configuration. ]]
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 [http://www.dibt.de/ approved firestops and fireproofing materials are available in Canada and the US.
Palusolmanschette.jpg|thumb|150px| A passive fire protection example of an intumescent with strong expansion pressure. This intumescent is called Palusol. It is based on using 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 waterborne intumescents. ]]
External links
See also
"Intumescent"