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Anintumescent substance is one that swells as a result ofheat exposure, leading to an increase involume and decrease indensity.Intumescence refers to the process of swelling.[1] Intumescent materials are typically used inpassive fire protection and requirelisting, approval, and compliance in their installed configurations in order to comply with the national building codes andlaws.[citation needed]
The details for individual building parts are specified in technical standards which are compiled and published by national or international standardization bodies like theBritish Standards Institute (BSI), theGerman Institute for Standardization (DIN), theAmerican Society for Testing and Materials (ASTM) or theInternational Organization for Standardization (ISO).
Intumescent coatings for steel constructions must be approved in standardized fire tests.
These intumescent materials produce a lightchar which is a poor conductor ofheat, thus retarding heat transfer. Typically the light char consists of microporous carbonaceous foam formed by a chemical reaction of three main components:ammonium polyphosphate,pentaerythritol, andmelamine.[2] The reaction takes place in a matrix formed by the molten binder which is typically based onvinyl acetate copolymers orstyreneacrylates.
Ablative coatings contain a significant amount ofhydrates. When the hydrates are heated, they decompose, and water vapour is released, which has a cooling effect. Once the water is spent, the insulation characteristics of the char that remains can retard heat transfer through the fire stop assembly.
Soft char products are typically used in thin film intumescent materials forfireproofing protection ofstructural steel as well as infirestop pillows.
Harder char is produced withsodium silicates andgraphite. These products are suitable for use inplasticpipefirestops in which applications it is necessary to exert expansionpressure to fill the gap left in the middle of the fire stop assembly left by the melting plastic pipe.
Intumescent coatings may be designed for protection of metals from fire, such asstructural steel. Reviews of the technology are available.[3] They may be based on a number of resin binders includingepoxy, and silicone.[4] Melamine-formaldehyde resin systems have been used using layered double-hydroxide modified phosphate esters that improved the intumescent properties.[5]
Some intumescent materials are susceptible to environmental influences such as humidity, which can reduce or negate their ability to function.[citation needed]
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