Intumescent materials expand when exposed to heat, providing passive fire protection in construction. They generate ash or foam, delaying the spread of fire, but can degrade over time due to humidity or UV radiation. Intumescents can be used in seals, coatings, and structural steel to increase fire resistance.
An intumescent is any material that expands when exposed to heat. Intumescent materials are typically used in construction to provide passive fire protection, in some cases delaying the spread of fire by up to an hour. Care should be taken when selecting an intumescent, because some are known to degrade over time, particularly due to humidity.
When exposed to temperatures above 300 degrees Fahrenheit (149 degrees Celsius), intumescents generate a thick layer of ash or foam, which conducts heat poorly and burns slowly. While the expansion of intumescent materials is typically 15-30 times their original thickness, some manufacturers claim expansions of up to 200 times. After the fire has burned through the first layer of insulating foam, it may reach another layer of intumescent, which will again form ash or additional foam.
With this cycle, the fire could be delayed until all intumescent material is used up. This process could take several minutes or up to an hour before the fire spreads further. If the fire is extinguished before the intumescent material is used up, the foam can be scraped off with minimal damage to the original structure.
Many intumescents contain chemically bound water and are endothermic. In this case, when exposed to fire, the intumescent will release water. This will help cool the surrounding areas.
There are several ways intumescent materials can be used to provide fire protection. Intumescent seals used in electrical boxes and fire doors provide fireproofing by significantly slowing the spread of a fire. While regular paint is highly flammable, an intumescent coating can be added to paint to provide significant fire protection. The fire resistance rating of structural steel can be increased by the application of intumescent coatings. Intumescent materials are also used within floor or wall assemblies as a fire blanket.
When exposed to high humidity, some materials will lose their intumescent properties, such as not generating as much foam or char in a fire. In fact, normal humidity is sufficient to degrade some intumescents. Some intumescents can also degrade due to exposure to ultraviolet radiation or heat. These sensitive intumescents may still be useful, but must always have a protective coating; if the coating wears off, the intumescent could degrade immediately. Several independent agencies test intumescent coatings and rate them on their tolerance to environmental stimuli and their fire resistance performance.
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