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Fireproofing

Spray gypsum based plaster fireproofing being installed.

Promat signum tray cladding 1

Circuit integrity fireproofing of cable trays, using calcium silicate boards.

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.

MarketsEdit

ApplicationsEdit

HistoryEdit

Asbestos was one material historically used for fireproofing, either on its own, or together with binders such as cement, either in sprayed form or in pressed sheets, or as additives to a variety of materials and products, including fabrics for protective clothing and building materials. Because the material has proven to cause cancer in the long run, a large removal and replacement business has been established.

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.

Alternative fireproofing methodsEdit

Among the conventional materials, purpose-designed spray fireproofing plasters have become abundantly available the world over. The inorganic methods include:

  • Gypsum plasters
  • Cementitious plasters
  • Fibrous plasters

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.

Unitherm2

See Image:Unitherm1.jpg. Intumescent spray fireproofing product has expanded.

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.

FraudEdit

The following examples of fraud are preventable when documentation is required and checked to ensure that all installed configurations fall within the tolerances of active certification listings.

  • Entraining too much air in inorganic systems, thus reducing densities, saves on materials and labour.
  • Spraying inorganic spray fireproofing materials over through-penetrations and building joints that should be firestopped, not fireproofed. This practice negates fire-separation integrity. Firestops must precede spray fireproofing.
    Beampenseal

    Firestopped through-penetrations of structural beams. The installation is incomplete, as the beams are not yet treated with fireproofing. If left as-is, they will collapse, resulting in openings in the fire separation wall.

  • Substitution of intumescent and/or endothermic fireproofing coatings with less expensive paints that physically resemble the passive fire protection products, sometimes involving re-use of packaging and de-canting of contents.
  • The American and Canadian nuclear industries have, historically, not insisted on listing and approval use and compliance, on the basis of the use of accredited certification laboratories. This has allowed the use of Thermo-Lag 330-1, for which the basis of testing has been proven to be faulty,[citation needed] resulting in millions of dollars of remedial work. The Thermo-Lag scandal came to light as a result of disclosures by American whistleblower Gerald W. Brown, who reported the deficiencies in fire testing to the Nuclear Regulatory Commission. Presently, product certification of fireproofing and firestopping remains optional for systems installed in nuclear power plants both in Canada and the United States.

Common errors in inorganic spray fireproofingEdit

  • Portland cement bound sprays display a high pH level at first. This has, at times, been presumed to last indefinitely, particularly for exterior spray fireproofing of large liquified petroleum gas containers, vessel skirts and pipe bridges. The proper primer must be used. The high pH of cement-borne plasters does not safeguard unprotected common steel substrata. Ignorance of this fact, particularly in coastal regions with high salt exposures has led to rusting and delaminations of spray fireproofing on large LPG spheres and other similar installations. Proper epoxies must be used for water-resistance to prevent "soaping" when in contact with the plaster.
  • The dew point calculations must be performed and considered where fibrous spray fireproofing on LPG spheres is installed. When this is not done, the dew point may be located inside of the spray fireproofing, which has resulted in ceramic fibre based sprays' becoming saturated with water.
  • Excessive mixing of cement-borne fireproofing results in having the cement stone formed and completely spent while still mixing, which causes a "spider-web" appearance of the finished plaster, because there was little or nothing of the binder left to actually "set" or "cure" when finally placed. This reduces the plaster to a "sand-castle" quality.
  • Spray fireproofing cannot be sprayed onto vibrating substrata, which can dislodge and weaken plasters.
  • Fresh cement plasters should be covered to reduce premature escape of water by exposure to wind and heat, resulting in lesser quality fireproofing plasters. The water is needed to form cement stone inside of the plaster.

Work stagingEdit

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 tunnel fireproofingEdit

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 exposed to hydrocarbon firesEdit

Concrete, by itself, cannot withstand hydrocarbon fires. In the Channel tunnel that connects United Kingdom and France, an intense fire broke out and reduced the concrete lining in the undersea tunnel down to about 50 mm.[citation needed] 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" [1] 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 [2].

Fireproofing concrete tunnel liningsEdit

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:

  • Existing traffic tunnel surfaces that are to be fireproofed must be cleaned to remove any substances that may impair proper bonding.
  • As traffic emissions darken new fireproofing products, light-reflecting coatings should be considered. They should be easy to clean, compatible with the substrate, and the combination of the fireproofing with the paint must be capable of absorbing the kinetic energy of spray cleaning.
  • In mountain tunnels, a space should be created between the fireproofing and the stone, for water traveling downwards through the mountain to be drained off, to avoid the formation of icicles and damage to the fireproofing system.

Fireproof VaultsEdit

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 is a very expensive and time-consuming process, so a vault design with a dry insulating material is peferable.

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 125 requirement are called data-rated vaults.

To achieve the Class 150 or 125 rating utilizing concrete as the barrier between the heat source and the information storage media is not a viable option for room-sized vaults. A dry insulating material with an extremely high temperature threshold is the most efficient way to circumvent the steam generation characteristic of concrete-type materials. Ceramic fiber[1] is a refractory material that has both the temperature insulating qualities and dry composition that make it ideal for protecting heat and humidity-sensitive media. Some vault manufacturers utilizes ceramic fiber for its modular vault panels[2] to achieve the stringent Class 150 and Class 125 ratings. The modular design allows the vaults to be expanded or relocated as needed. Upper floor vaults are also viable due to the lightweight nature of ceramic fiber insulation.

To comply with NFPA standards[3] 75 (for protection of electronic equipment) and NFPA 232 (for protection of vital records, including media) all components of fireproof vaults must meet the fire protection rating of the vault itself. This includes the doors, HVAC penetrations and cable penetrations. NFPA standards also require an automatic door closer system[4] so personnel are not required to seal the vault in the event of fire. Because there is no single door that can meet the Class 125 rating, a double door assembly is needed. The most commonly used combination of doors to reach the Class 125 rating is an outer Class 350-4 Hour door [5] and an inner 225-3 Hour door.

Aside from protecting computer backup tapes and other media, Class 125 vaults are often used in data centers to protect mission critical IT equipment.

See alsoEdit

ReferencesEdit

  1. Specifications of ceramic fiber blanket material
  2. Class 125 vault components
  3. National Fire Protection Association Codes and Standards
  4. Automatic door closer information
  5. Class 350-4 Hour door specifications

External LinksEdit

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