Intumescent

From Wikipedia, the free encyclopedia

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 bounding installations in order to comply with the law.

1 The role of water
2 Uses of intumescents in passive fire protection
3 Problems with intumescents
4 Gallery
5 References
6 See also
7 External links

Intumescents are typically endothermic to varying degrees, as they can contain chemically bound water.^[1] 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 water-bearing 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 will resume increasing.

Intumescents are used in firestopping, fireproofing and gasketing applications, in buildings, offshore construction, ships, and aircraft.

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 US.^[2]

Low Pressure Intumescent Resin: This product is suitable for use in passive fire protection in general, firestopping and 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.	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 enough 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.	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.	Intumescent gasketing used in passive fire protection, for fire door applications. Typically, such gasketing is needed to pass positive pressure furnace testing, a recent change in North America.
Intumescent putty, permanently pliable, used in a cable penetration firestop. Permanently pliable putties are similar in consistency to play-dough used for children's toys. Putties of this nature also lend themselves to be used as pads to cover electrical outlet boxes inside drywall assemblies required to have a fire-resistance rating. The endothermic and insulative action of the pads reduce thermal transfer through the metallic outlet box to the unexposed side of the rated drywall assembly. All intumescents must be installed in a manner consistent with bounding requirements.	A 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.	Construction of a test sample, consisting of a mock-up concrete floor frame, complete with penetrants. The concrete frame measures approximately 5’ x 9’ x 4" (ca. 1.5m x 2.3m x 10cm). It has a large hole in the centre with many mechanical and electrical services traversing. The penetrants extend 1’ (30cm) into the furnace and 3’ (91cm) on the unexposed side. A firestop mortar is being applied here. Notice the intumescent wrap strip surrounding the fibreglass pipe insulation. When the fire starts, this embedded intumescent will swell to take up the place of the melting insulation. The test was conducted in accordance with the Canadian firestop test method ULC in Scarborough, Ontario.^[3]