FIRE PROOFING

F-I-R-E P-R-O-O-F-I-N-G





Example of spray fireproofing, using a gypsum based plaster in a low-rise industrial building in Vancouver, British Columbia. The plaster provides a layer of insulation to retard heat flow into structural steel to prevent collapse.

Delaminated spray fireproofing at Cambrian College, Greater Sudbury, Ontario, Canada, August 2000.

Pre-mixed fireproofing Plaster stored on construction site, ready to spray onto structural steel.

Applications of FIRE PROOFING

• Structural steel to keep below critical temperature ca. 540 °C
• Electrical circuits to keep critical electrical circuits below 140 °C so they stay operational
• Liquefied 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 the material has proven to be causing 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 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 BS4

76, 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 inorganic 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 contr

avening 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.

Pipes covered with a thin-film intumescent spray fireproofing product called Unitherm. As the flame from the blow-torch hits it, the intumescent expands, forming a layer of insulation, which slows down heat transfer to the pipe below. Hydrates within the coating give up their water content, maintaining a temperature near the boiling point of 100 °C.

In this picture, the flame has been removed after the thin-film intumescent spray fireproofing product has been completely expanded. Some intumescents can undergo shrinkage shortly after full expansion has taken place.

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.

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.

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, 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, 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.

• Fireproofing concrete tunnel linings

In essence, this is really not much different from protecting structural steel or electrical circuits or valves. The 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. 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.