Fireproofing: Difference between revisions
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* [[Tunnel]] [[concrete]] walls and ceilings or linings |
* [[Tunnel]] [[concrete]] walls and ceilings or linings |
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* Under and above ground mining operations |
* Under and above ground mining operations |
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* Poop Incorperated |
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==Applications== |
==Applications== |
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Revision as of 04:02, 19 June 2007
- "Fireproof" redirects here. For the album, see Fireproof (album).
Fireproofing, a passive fire protection measure, subject to bounding, 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 bounded fireproofing system to certain structures allows these to have a fire-resistance rating. However, by no means does fireproofing allow treated items to be entirely unaffected by any fire. No conventional materials are immune to the effects of fire at a sufficient intensity and/or duration.
Markets
- Commercial construction
- Residential construction
- Industrial construction
- Marine (ships)
- Offshore construction
- Aerodynamics
- Tunnel concrete walls and ceilings or linings
- Under and above ground mining operations
Applications
- Structural steel to keep below critical temperature ca. 540 °C
- Electrical circuits to keep critical electrical circuits below 140 °C so they stay operational
- Liquified petroleum gas containers to prevent a BLEVE (boiling liquid expanding vapour explosion)
- Vessel skirts and pipe bridges in an oil refinery or chemical plant to keep below critical temperature ca. 540°
- Concrete linings of traffic tunnels
History
Asbestos is 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 of the litigation associated with asbestos, 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 even 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 methods
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
Manufacturers for these inorganics are in a constant, competitive struggle for commercial success against one another. The competition focuses simply on managing to obtain fire-resistance ratings at the lowest possible cost. Simply, the idea is to become faster and cheaper than the competition.
The industry considers gypsum-based plasters to be "cementitious", even though these contain no portland cement, let alone calcium alumina cement. Cementitious plasters that actually 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, again, in an effort to reduce the density, which generally makes for a more effective insulation as well as a lower cost. The resulting plaster has still 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 bounding can, at times further enhance such displacement of solids, which has led many architects to insist on the use of on-site testing of proper densities to ensure that they are getting what they're paying for, as excessively light inorganic fireproofing does not provide adequate protection.
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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 go on like paint 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 work well, they tend to be banned from use inside of buildings and are thus 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. Europeans 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.
Fraud
All these types of fraud can be summarised as violations of bounding, all of which 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 can result in token extras paid to spray fireproofers at the peril of fire-separation integrity. Firestops must precede spray fireproofing!
- 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 has occurred in the past.
- The American and Canadian nuclear industries have, historically, not insisted on bounding, on the basis of the use of accredited certification laboratories. This has resulted in the use of Thermo-Lag 330-1, on the basis of testing that has been proven to be faulty and has resulted in millions of dollars worth 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. Still, to this day, product certification of fireproofing and firestopping measures is optional for systems installed in nuclear power plants both in Canada and the United States.
Common errors in inorganic spray fireproofing
- 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. One must use proper primer. 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 obscene rusting and delaminations of spray fireproofing on large LPG spheres and more. Proper epoxies must be used for water-resistance to prevent "soaping" when in contact with the plaster.
- Fibrous spray fireproofing on LPG spheres have, at times ignored the necessary dew point calculations, resulting in having ceramic fibre based sprays become totally saturated with water, which has led to other problems.
- Spray fireproofers unfamiliar with and perhaps apathetic about the basic chemistry that governs the forming of cement stone, have been known to go on break, while bags of spray fireproofing mixtures were turning, with water, in mixing drums, ready to be sprayed when workers returned from lunch breaks. Of course, excessive mixing leaves the cement perfectly spent, no longer able to form any more cement stone once placed, resulting in a "spider-web" appearance of the finished plaster, as its setting ability has been largely diminished, the plaster reduced to "sand-castle" quality.
- Spray fireproofers have been known in industrial settings to spray onto vibrating substrata, which can dislodge and weaken plasters.
- Spray fireproofers unfamiliar with basic cement chemistry have been known to have their plasters weakened by common cement poisons, such as high wind and heat exposures to fresh plasters, which should have been suitably covered to reduce premature escape of water, that is needed to form cement stone inside of the plaster. This has resulted in lesser quality fireproofing plasters.
Work staging
Typically, it is necessary for firestopping to be completed before fireproofing. It is a common short-cut and code violation, to get one's fireproofer to spray areas near the top of fire barriers, as this is very cheap and tends to put a veneer of fireproofing where firestopping should be seen.
No bounding is possible in this manner, as spray fireproofing products have not been qualified to the thousands of firestop configurations. When such staging is being newly enforced on construction sites, disputes can occur, as it takes a lot more labour for a spray fireproofer to have to go from room to room, if that is even possible, depending on the size of the equipment. In hospitals, in particular, not allowing for that extra labour can be prohibitively expensive.
Traffic tunnel fireproofing
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 heat rise and high heat (see the hydrocarbon curves in fire-resistance rating). It is a known fact in tunnel construction and operations, that where hydrocarbon transports are permitted, accidental fires may occur, causing spilled loads amidst sparks. It is, therefore, prudent to fireproof concrete linings of traffic tunnels. Traffic tunnels are not ordinarily equipped with fire suppression means. It is very difficult to overcome hydrocarbon fires by active fire protection means or to so equip an entire tunnel along its whole length for the eventuality of a hydrocarbon fire or a BLEVE, which then destroys everything in its path, until the fuel is spent.
- What happens to concrete in hydrocarbon fires?
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 [2], iBMB TU Braunschweig [3], which headed the "Eureka" [4] 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, or 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, each of which must be able to prove bounding in accordance with the hydrocarbon fire test curve, such as the one that is also used in UL1709 [5].
- Fireproofing concrete tunnel linings
In essence, this is really not much different from protecting structural steel or electrical circuits or valves. Te most important item is to maintain strict bounding. Next, one must slow down the heat transfer into the item to be protected. 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. Examples of purpose-made tunnel fireproofing can be seen here [6]. Other things to be kept in mind are as follows:
- If one is fireproofing existing traffic tunnels, one must ensure proper cleaning of the concrete to remove any substances that may impair proper bonding.
- Lighting concerns must be kept in mind. Traffic darkens new fireproofing products. One must, therefore, investigate proper, light-coloured coatings, which reflect light, are easy to clean, are compatible with the substrate and that the combination of the two are also to absorb the kinetic energy of spray cleaning.
- In mountain tunnels, one must ensure that a space is created between the fireproofing and the stone, for water traveling downwards through the mountain to be drained off, to avoid the formation of dangerous icicles and damage to the fireproofing system.
Trade jusrisdiction on unionised construction sites in North America
- Structural Steel and Concrete Substrata: Plasterers plastering [7]
- Electrical Circuits: Insulators [8]
- Ductwork: Insulators [9]
See also
