An intumescent substance is one that swells as a result of

heat In thermodynamics, heat is energy in transfer between a thermodynamic system and its surroundings by such mechanisms as thermal conduction, electromagnetic radiation, and friction, which are microscopic in nature, involving sub-atomic, ato ...

exposure, leading to an increase in

volume Volume is a measure of regions in three-dimensional space. It is often quantified numerically using SI derived units (such as the cubic metre and litre) or by various imperial or US customary units (such as the gallon, quart, cubic inch) ...

and decrease in

density Density (volumetric mass density or specific mass) is the ratio of a substance's mass to its volume. The symbol most often used for density is ''ρ'' (the lower case Greek letter rho), although the Latin letter ''D'' (or ''d'') can also be u ...

. Intumescence refers to the process of swelling. Intumescent materials are typically used in

passive fire protection Passive fire protection (PFP) is components or systems of a building or structure that slows or impedes the spread of the effects of fire or smoke without system activation, and usually without movement. Examples of passive systems include floor- ...

and require listing, approval, and compliance in their installed configurations in order to comply with the national building codes and

law Law is a set of rules that are created and are enforceable by social or governmental institutions to regulate behavior, with its precise definition a matter of longstanding debate. It has been variously described as a science and as the ar ...

s. The details for individual building parts are specified in technical standards which are compiled and published by national or international standardization bodies like the

British Standards Institute The British Standards Institution (BSI) is the Standards organization, national standards body of the United Kingdom. BSI produces technical standards on a wide range of products and services and also supplies standards certification services ...

(BSI), the

German Institute for Standardization German(s) may refer to: * Germany, the country of the Germans and German things **Germania (Roman era) * Germans, citizens of Germany, people of German ancestry, or native speakers of the German language ** For citizenship in Germany, see also Ge ...

(DIN), the

American Society for Testing and Materials American(s) may refer to: * American, something of, from, or related to the United States of America, commonly known as the "United States" or "America" ** Americans, citizens and nationals of the United States of America ** American ancestry, p ...

(ASTM) or the

International Organization for Standardization The International Organization for Standardization (ISO ; ; ) is an independent, non-governmental, international standard development organization composed of representatives from the national standards organizations of member countries. M ...

(ISO). Intumescent coatings for steel constructions must be approved in standardized fire tests.

Types

Soft char

These intumescent materials produce a light char which is a poor conductor of

, 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 Pentaerythritol is an organic compound with the formula C(CH2OH)4. The molecular structure can be described as a neopentane with one hydrogen atom in each methyl group replaced by a hydroxyl (–OH) group. It is therefore a polyol, specifically a ...

, and

melamine Melamine is an organic compound with the formula C3H6N6. This white solid is a trimer (chemistry), trimer of cyanamide, with a 1,3,5-Triazine, 1,3,5-triazine skeleton. Like cyanamide, it contains 66% nitrogen by mass, and its derivatives ha ...

. The reaction takes place in a matrix formed by the molten binder which is typically based on

vinyl acetate Vinyl acetate is an organic compound with the Chemical formula, formula CH3CO2CH=CH2. This colorless liquid is the precursor to polyvinyl acetate, ethylene-vinyl acetate copolymers, polyvinyl alcohol, and other important industrial polymers. Prod ...

copolymers or

styrene Styrene is an organic compound with the chemical formula C6H5CH=CH2. Its structure consists of a vinyl group as substituent on benzene. Styrene is a colorless, oily liquid, although aged samples can appear yellowish. The compound evaporates easi ...

acrylates. Ablative coatings contain a significant amount of

hydrate In chemistry, a hydrate is a substance that contains water or its constituent elements. The chemical state of the water varies widely between different classes of hydrates, some of which were so labeled before their chemical structure was understo ...

s. 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 for

fireproofing Fireproofing is rendering something (Building, structures, materials, etc.) resistant to fire, or incombustible; or material for use in making anything fire-proof. It is a passive fire protection measure. "Fireproof" or "fireproofing" can be u ...

protection of

structural steel Structural steel is steel used for making construction materials in a variety of shapes. Many structural steel shapes take the form of an elongated beam having a profile of a specific cross section (geometry), cross section. Structural steel sha ...

as well as in firestop pillows.

Hard char

Harder char is produced with

sodium silicate Sodium silicate is a generic name for chemical compounds with the formula or ·, such as sodium metasilicate (), sodium orthosilicate (), and sodium pyrosilicate (). The anions are often polymeric. These compounds are generally colorless tra ...

s and

graphite Graphite () is a Crystallinity, crystalline allotrope (form) of the element carbon. It consists of many stacked Layered materials, layers of graphene, typically in excess of hundreds of layers. Graphite occurs naturally and is the most stable ...

. These products are suitable for use in

plastic Plastics are a wide range of synthetic polymers, synthetic or Semisynthesis, semisynthetic materials composed primarily of Polymer, polymers. Their defining characteristic, Plasticity (physics), plasticity, allows them to be Injection moulding ...

pipe

firestop A firestop or fire-stopping is a form of passive fire protection that is used to seal around openings and between joints in a fire-resistance-rated wall or floor assembly. Firestops are designed to maintain the fire-resistance rating of a wall ...

s in which applications it is necessary to exert expansion

pressure Pressure (symbol: ''p'' or ''P'') is the force applied perpendicular to the surface of an object per unit area over which that force is distributed. Gauge pressure (also spelled ''gage'' pressure)The preferred spelling varies by country and eve ...

to fill the gap left in the middle of the fire stop assembly left by the melting plastic pipe.

Intumescent coatings

Intumescent coatings may be designed for protection of metals from fire, such as

. Reviews of the technology are available. They may be based on a number of resin binders including

epoxy Epoxy is the family of basic components or Curing (chemistry), cured end products of epoxy Resin, resins. Epoxy resins, also known as polyepoxides, are a class of reactive prepolymers and polymers which contain epoxide groups. The epoxide fun ...

, and silicone. Melamine-formaldehyde resin systems have been used using layered double-hydroxide modified phosphate esters that improved the intumescent properties.

Problems

Some intumescent materials are susceptible to environmental influences such as humidity, which can reduce or negate their ability to function.

Gallery

File:Intumescent.jpg, Low pressure intumescent resin: This product is suitable for use in

in general, and in

ping and interior fireproofing in particular. The small, orange chunk on the bottom right is capable of growing into the large black object above and to its left. File:Unitherm.jpg, Pipe covered with a thin-film intumescent spray fireproofing File:Unitherm2.jpg, In this picture, the flame has been removed after the thin-film intumescent spray fireproofing product has completely expanded. File:Intumescent door gasket.svg, Intumescent gasketing used in

, for

fire door A fire door is a door with a fire-resistance rating (sometimes referred to as a ''fire protection rating'' for closures) used as part of a passive fire protection system to reduce the spread of fire and smoke between separate compartments of ...

applications.

References

External links

"The proof is in the fire" Chemical Innovation Magazine, American Chemical SocietyAmerican Chemical Society: Fire Retardancy of Polypropylene Composites Using Intumescent Coatings
{{Fire protection Materials Firestops