Textiles for use indoors are soaked in fire-retardant solutions made up mostly of boric acid and borax. Textiles for outdoors are soaked with chlorinated paraffin, chlorinated synthetic resins, or chlorinated rubber. The standard for effectiveness of these treatments is the weight of chemicals remaining after the materials dry. Large areas of textiles are brushed or sprayed, but they gain little resistance against severe fire exposure; the treatment is mainly a guard against lit cigarettes and short exposure to flame.
Rain, washing, or dry cleaning tends to leach the chemicals from the fabric; therefore latex is often added to waterproof the material. At one time asbestos could be mixed with natural fibers to increase their fire resistance, but now only glass or ceramic fibers are permitted. The fire resistance of a textile is generally expressed in hours of endurance to a standard temperature furnace.
In construction, heavy wood timbers have a relatively high fire resistance, because fire tends to burn very slowly inward from the surface, leaving enough sound timber in the center to prevent collapse. Wood framing can also be impregnated with ammonium phosphate solution or covered with special mastics. Stucco or other incombustible facing also gives a wood frame some protection from fire.
To be classed as fire resistive, buildings must be made of reinforced concrete or protected steel that will stand considerable fire with minor damage; even a building made of unprotected steel may be damaged. While steel retains its strength up to a very high temperature, it fails rapidly at temperatures over 1,000°F; (540°C;). Structural steel may be protected in a number of ways. It can be faced with brick, concrete, or tile; however, construction with these materials usually adds too much weight to a building. A protective layer of concrete over all surfaces of a beam or over the steel bars in reinforced concrete has to be at least 2.5 in. (6.4 cm) thick to be effective; hollow clay tile used to cover beams and girders has to be at least 4 in. (10 cm) thick. Thus most buildings use lightweight fireproofing such as gypsum, perlite, and vermiculite mixed in plaster, concrete, and mineral fiber; one inch (2.5 cm) of such materials will absorb an equivalent amount of heat as 2.5 in. (6.4 cm) of concrete.
Some recent buildings circulate water inside each column, protecting the structure against meltdown. Asbestos is no longer used, because inhalation of the fibers causes abestosis, a fatal lung disease; fireproof board made from a mixture of asbestos and cement is used only rarely. Concrete is still used, but mostly as a thin slab on floors. In urban areas, buildings must also provide protection against fire in neighboring buildings through fireproof exterior walls—preferably windowless, since windows are fire openings. Standards for fireproofing are set by organizations such as the American Insurance Association and the International Conference of Building Officials.
Fireproofing, a passive fire protection measure, refers to the act of making materials or structures more resistant to fire, or to those materials themselves, or the act of applying such materials. Applying a certification listed fireproofing system to certain structures allows these to have a fire-resistance rating. The term, fireproof, does not necessarily mean that an item cannot ever burn: It relates to measured performance under specific conditions of testing and evaluation. Fireproofing does not allow treated items to be entirely unaffected by any fire, as conventional materials are not immune to the effects of fire at a sufficient intensity and/or duration.
Endothermic materials have also been used to a large extent and are still in use today, such as gypsum, concrete and other cementitious products. More highly evolved versions of these are used in aerodynamics, intercontinental ballistic missiles (ICBMs) and re-entry vehicles, such as the space shuttles.
The use of these older materials has been standardised in "old" systems, such as those listed in BS476, DIN4102 and the National Building Code of Canada.
The industry considers gypsum-based plasters to be "cementitious", even though these contain no portland cement, or calcium alumina cement. Cementitious plasters that contain portland cement have been traditionally lightened by the use of inorganic lightweight aggregates, such as vermiculite and perlite.
Gypsum plasters have been lightened by using chemical additives to create bubbles that displace solids, thus reducing the bulk density. Also, lightweight polystyrene beads have been mixed into the plasters at the factory in an effort to reduce the density, which generally results in a more effective insulation at a lower cost. The resulting plaster has qualified to the A2 combustibility rating as per DIN4102. Fibrous plasters, containing either mineral wool, or ceramic fibres tend to simply entrain more air, thus displacing the heavy fibres. On-site cost reduction efforts, at times purposely contravening the requirements of the certification listing, can further enhance such displacement of solids. This has resulted in architects' specifying the use of on-site testing of proper densities to ensure the products installed meet the certification listings employed for each installed configuration, because excessively light inorganic fireproofing does not provide adequate protection and are thus in violation of the listings.
New materials based on organic chemistry are gaining in popularity for a variety of reasons. In land-based construction, thin-film intumescents have become more widely used. Unlike their inorganic competitors, thin-film intumescents are installed like paint, except that the purpose is to achieve a certain thickness, not just to apply a different colour, and do not require the concealment of structural steel elements such as I-beams and columns. Care must be taken to ensure that such products are protected from atmospheric moisture and operational heat, which can adversely affect these organic, covalently bound products. The use of DIBt approved products, which mandates testing of the effects of ageing, is prudent.
Thicker intumescent and endothermic resin systems tend to use an oil basis (usually epoxy), which, when exposed to fire, creates so much smoke, that even though these products provide enough heat flow retardation towards the substrate, they tend to be banned from use inside of buildings because of the smoke they develop when subjected to fire, and are used mainly in exterior construction, such as LPG vessels, vessel skirts and pipe bridges in oil refineries, chemical plants and offshore oil and gas platforms.
Proprietary boards and sheets, made of gypsum, calcium silicate, vermiculite, perlite, mechanically bonded composite boards made of punched sheet-metal and cellulose reinforced concrete (DuraSteel) have all been used to clad items for increased fire-resistance. Cladding is traditionally much more popular and organised in Europe than in North America. Fringe methods have also included intumescent tapes and sheets, as well as endothermically treated ceramic fibre sheets and roll materials. The latter work well but are not particularly popular due to cost reasons. Ordinary ceramic fibre, typically encased in thin aluminium foil is often used to protect pressurisation ductwork and grease ducts in North America. Such mineral wool (rock wool) wraps have been used in Europe for decades more than in North America. European construction sites tend to use much less expensive mineral wool wraps for duct fireproofing. All are qualified to the same test regime: ISO6944, with the exception that systems qualified for the North America market also undergo a hose-stream test immediately following the fire exposure in order to validate the firestop portion of the system.
Spray fireproofing products have not been qualified to the thousands of firestop configurations, so they cannot be installed in conformance of a certification listing. Therefore, firestopping must precede fireproofing. Both need one another. If the structural steel is left without fireproofing, it can damage fire barriers and a building can collapse. If the barriers are not firestopped properly, fire and smoke can spread from one compartment to another.
Traffic tunnels may be traversed by vehicles carrying flammable goods, such as petrol, liquified petroleum gas and other hydrocarbons, which are known to cause a very rapid temperature rise and high ultimate temperatures in case of a fire (see the hydrocarbon curves in fire-resistance rating). Where hydrocarbon transports are permitted in tunnel construction and operations, accidental fires may occur, resulting in the need for fireproofing of traffic tunnels with concrete linings. Traffic tunnels are not ordinarily equipped with fire suppression means, such as fire sprinkler systems. It is very difficult to control hydrocarbon fires by active fire protection means, and it is expensive to equip an entire tunnel along its whole length for the eventuality of a hydrocarbon fire or a BLEVE.
Concrete, by itself, cannot withstand hydrocarbon fires. In the Channel tunnel that connects England and France, an intense fire broke out and reduced the concrete lining in the undersea tunnel down to about 50 mm. In ordinary building fires, concrete typically achieves excellent fire-resistance ratings, unless it is too wet, which can cause it to crack and explode. For unprotected concrete, the sudden endothermic reaction of the hydrates and unbound humidity inside the concrete causes such pressure as to spall off the concrete, which then winds up in small pieces on the floor of the tunnel. This is the reason why laboratories, which conduct fire-resistance testing, such as ULC, iBMB TU Braunschweig, which headed the "Eureka" project, or Underwriters Laboratories insert humidity probes into all concrete slabs that undergo fire testing even in accordance with the less severe building elements curve (DIN4102, ASTM E119, BS476, or ULC-S101). Only once the humidity is low enough, will a fire test be conducted because otherwise explosions would result. The culprit is the hydrates and unbound humidity in the concrete, and this is not new. Another prime example of this is the fact that walls constructed of lost plastic forms, which are filled on site with concrete cannot withstand the testing required of a loadbearing Firewall (construction). During the fire test, these walls are subjected to a load, which then leads to such a forceful explosion as to shear the wall with thunderous noise. A hydrocarbon fire is much more rapid and severe than a typical building fire. Consequently, concrete is much more vulnerable and must be protected in order to remain operable during a hydrocarbon fire. The need for fireproofing was demonstrated, among other fire protection measures, in the European "Eureka" Fire Tunnel Research Project, which resulted in building codes for the trade to avoid the effects of such fires upon traffic tunnels. Cementitious spray fireproofing must be certification listed and applied in the field as per that listing, using a hydrocarbon fire test curve such as the one that is also used in UL1709
In essence, this is really not much different from protecting structural steel or electrical circuits or valves. The systems must be installed in accordance with the requirements of the certification listing. Heat transfer into the item to be protected must be limited. This is accomplished by the use of firm fireproofing products, such as higher density fireproofing plasters or fireproofing boards, such as those made of calcium silicate or vermiculite. Other things to be kept in mind are as follows:
The traditional method for constructing fireproof vaults to protect important paper documents has been to use concrete or masonry blocks as the primary building material. In the event of a fire, the chemically bound water within the concrete or masonry blocks will be forced into the vault chamber as steam. The steam will soak the paper documents to keep them from burning. This steam will also help keep the temperature inside the vault chamber below the critical 350-degree Fahrenheit (176.7-degrees Celsius) threshold, which is the point at which information on paper documents is destroyed. The paper can later be remediated with a freeze drying process, if the fire is extinguished before internal temperatures exceed 350-degrees F.
This traditional vault construction method is sufficient for paper documents, but the steam generated by concrete/masonry structures will destroy contents that are more sensitive to heat and moisture. For example, information on microfilm is destroyed at just 150-degrees F. (65.5-degrees C. a.k.a. Class 150) and magnetic media (such as data tapes) lose data above 125-degrees F. (51.7-degrees C. a.k.a. Class 125). Fireproof vaults built to meet the more stringent Class 150 and Class 125 requirements are called data-rated vaults.
Help wanted: a spray fireproofing contractor emphasizes education and involvement to strengthen the industry's muscles and influence.
Sep 01, 2006; I am the owner and operator of a fireproofing and specialty coatings contracting firm. I represent the fifth generation of...