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Description
Fire protection has been recognized as a crucial part of public and commercial building design for decades. Following the collapse of the World Trade Center towers on September 11, 2001, increased attention has been focused on the need to ensure that adequate fire protection is incorporated and maintained in buildings where large numbers of people may be present. Thus, fire-resistant coatings, which have been available since the 1960s, have been receiving increased attention. These specialty coatings can help lengthen the time that structural materials can maintain their integrity under fire conditions.
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Fireproofing is recognized to play a crucial role in establishing building safety and generally refers to the protection of the structural steel and other supporting parts in a building. Traditional fireproofing materials include concrete encasement, gypsum wallboard, and coatings categorized as Spray-Applied Fire-Resistive Materials (SFRMs) that are typically composed of ingredients such as mineral wool, cement, and gypsum, and can very in density. Intumescent fire-resistive coatings are newer fireproofing materials. They are paint-like coatings that are applied to structural steel members at a final thickness from 0.03 to 0.50 inches.
All of these fireproofing materials are designed to provide an insulating barrier between the heat from a fire and the structural steel. The barrier prevents the high temperatures within a fire from affecting the structural performance of the steel members. Because the intumescent coatings have paint-like properties, they are receiving increasing attention from architects and designers.
FIRE RETARDANT VS. FIRE RESISTANT
There are actually two types of "fire" coatings on the market. They are designed for use on different substrates and respond very differently when exposed to fire.
Fire-retardant paints are applied to combustible materials (wood, plastic, foam) and are designed to reduce the rate of flame spread. Typically, they are based on vinyl or vinyl acrylic resins. They look like paints and are formulated to be applied like paints (brush, roller, or spray). They do burn, can generate smoke, and do not have high temperature resistance.
The standard ASTM test for fire-retardant paints is ASTM E 84, which lasts for 15 minutes. The test evaluates flame spread and smoke development. Coatings that are meant to protect combustible substances are tested on Douglas-fir and are classified as either Class A, B, or C. The classification is determined via a comparison to red oak.
Many fire-retardant coatings are only rated for the ability to "not contribute" to a fire, i.e. they will not become a fuel source. Some do provide resistance in keeping the fire from getting to the substrate. Most create a soft char that will not keep plastics from melting and dripping into a fire. Some do not do a good job of preventing rapid heat transfer through metal. Smoke management is another, even more critical (and difficult to address) requirement. The smoke generation due to substrate/coating interaction will be different for different fire-retardant paint/substrate combinations and must also be designed into a robust coating system.
Fire-resistant coatings provide insulation to the substrate. Intumescent fire-resistant coatings work by expanding their volume from 10 to 75 times and generating an ash-like char. The extent of char will be dependent upon the material contained in the coating. The shape of the structural steel will affect expansion and char formation.
These coatings provide fire ratings (1, 2, 3, and 4 hours) depending on the coating thickness, steel shape, and steel mass. Adhesion, char integrity, and char growth are critical. The standard test for these materials for a cellulosic fire is ASTM E 119 (UL 263, NFPA 251), which involves placement of the coated part in a furnace for 1-4 hours. UL 1709 is the test used when it is necessary to simulate a hydrocarbon fire, which can reach very high temperatures very quickly (2,000[degrees]F within five minutes).
Fire-resistant coatings are applied in much greater thicknesses than fire-retardant coatings, and are either sprayed or troweled on. The rheology of these formulations is designed so that the coating hangs at a high film build. The level of film build varies from manufacturer to manufacturer and product to product.
BUILDING CODES AND APPROPRIATE APPLICATIONS
Fire protection requirements are established in various building codes. In the past, three model... |
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