Fire resistance, 3.28

Epoxy resin does not bear temperatures higher than 80-KX) °C once it has exceeded this value, it melts, compromising the bonding of the fibrous component of the structure. This means that FRP reinforced structures, if exposed to a potential fire 

Flame-retardant additives work by acting chemically and/or physically in the condensed phase or gas phase. The types of flame-retardant additives and their operating characteristics are described below. 

Char formers Usually phosphorus compounds, which remove the carbon fuel source and provide an insulation layer against the fire s heat 

Heat absorbers Usually metal hydrates such as aluminum trihydrate (ATH) or magnesium hydroxide, which remove heat by using it to evaporate water in their structure 

Flame quenchers Usually bromine- or chlorine-based halogen systems that interfere 

Synergists Usually antimony compounds, which enhance performance of the flame 

This section does not deal with finely divided aluminium in the form of powder or granules. It is well known that alurniniurn, like many other metals, is flammable in the finely divided state. Parenthetically, aluminium powder has pyrotechnic applications and is used in solid rocket boosters (Ariane, etc.). 

Regulations on the use of metallic materials as a building material, in ship building, transport, etc. are also beyond the scope of this book. 

The melting point of aluminium is 660 °C. Only two other common metals have a lower melting point magnesium (650 °C) and zinc (419 °C) (Table G.7.1). In practice, as the temperature exceeds 660 °C, aluminium structures will melt but not burn. 

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Nomex is another aramid fiber Kevlar and Nomex differ only in that the substitution pattern in the aromatic rings is para in Kevlar but meta in Nomex Nomex is best known for its fire resistant properties and is used in protective clothing for fire fighters astronauts and race car drivers... 

The inherent fire resistance and low smoke properties of furan resins appear to be related to the high degree of charring that takes place with minimum evolution of volatiles when exposed to fire. 

Pentaerythritol is used in self-extinguishing, non dripping, flame-retardant compositions with a variety of polymers, including olefins, vinyl acetate and alcohols, methyl methacrylate, and urethanes. Phosphoms compounds are added to the formulation of these materials. When exposed to fire, a thick foam is produced, forming a fire-resistant barrier (see Elame retardants) (84—86). 

Fire Resista.nce. Many fillers, particularly inorganic oxides, are noncombustible and provide a measure of passive fire resistance to filled plastics by reducing the volume of combustible matter in the filled composition. Depending on their density, they may also serve as insulation. 

Fillers that contain combined water or carbon dioxide, such as alumina trihydrate, Mg(OH)2, or dawsonite [12011 -76-6] increase fire resistance by hberating noncombustible gases when they are heated. These gases withdraw heat from the plastic and can also reduce the oxygen concentration of the air surrounding the composition. 

Useful materials incorporating fire-retardant additives are not always straightforward to produce. Loadings of 10% are common, and far higher levels of flame retardants are used in some formulations. These concentrations can have a negative effect on the properties and functions for which the materials were originally intended. Product-specific trade-offs are generally necessary between functionaUty, processibiUty, fire resistance, and cost. 

Dehydration or Chemical Theory. In the dehydration or chemical theory, catalytic dehydration of ceUulose occurs. The decomposition path of ceUulose is altered so that flammable tars and gases are reduced and the amount of char is increased ie, upon combustion, ceUulose produces mainly carbon and water, rather than carbon dioxide and water. Because of catalytic dehydration, most fire-resistant cottons decompose at lower temperatures than do untreated cottons, eg, flame-resistant cottons decompose at 275—325°C compared with about 375°C for untreated cotton. Phosphoric acid and sulfuric acid [8014-95-7] are good examples of dehydrating agents that can act as efficient flame retardants (15—17). 

Numerous tests covering flame retardancy and related matters are available. The requirements most often specified for fire resistance of a textile materials are that it must pass either Federal Specification Method 5903 or NFPA 701. 

Finally, a modification has been carried out in which a polyacrylate emulsion is added to a normal tetrakis(hydroxymethyl)phosphonium sulfate [55566-30-8] (THPS), urea, and TMM fire-retardant treatment in an attempt to completely alleviate the strength loss during the finishing. Indeed, better retention of tensile properties is achieved with no loss in fire resistance (85). 

Cotton—Wool Blends. Although they command only a very small fraction of the cotton blend market, cotton—wool blends are easier to make fire resistant than cotton itself. As might be expected, twiU fabrics containing both cotton and wool had decreased burning rates and increased 01 values both before and after fire-retardant treatment (147). 

W. A. Reeves, G. L. Drake, Jr., and R. M. Perkins, Fire-Resistant Textiles Handbook, Technomic Publishing Co., Inc., Westport, Conn., 1974. 

The largest volume of hydrauHc fluids are mineral oils containing additives to meet specific requirements. These fluids comprise over 80% of the world demand (ca 3.6 x 10 L (944 x 10 gal))- In contrast world demand for fire-resistant fluids is only about 5% of the total industrial fluid market. Fire-resistant fluids are classified as high water-base fluids, water-in-oil emulsions, glycols, and phosphate esters. Polyolesters having shear-stable mist suppressant also meet some fire-resistant tests. 

Fire-Resistant Hydraulic Fluids. The four classifications of fire-resistant hydrauHc fluids are Hsted below (7). Three of the four groups are fire resistant because they contain a significant amount of water which provides cooling and blanketing of the combustible materials. 

The compressibihty and thermal conductivity of mineral oils is compared to fire-resistant fluids in Table 3. All good hydrauHc fluids must resist compression, and many fire-resistant fluids can operate at a lower temperature than mineral oils because of improved thermal conductivity. 

Some of the tests and criterion used to define fire resistance may be found in the Hterature (9). Additionally, the compression—ignition and hot manifold tests as defined in MIL-H-19457 and MIL-H-5606, respectively the Wick test as defined by Federal Standards 791, Method 352 flash point and fire point as defined in ASTM D92 autoignition temperature as defined in ASTM D2155 and linear flame propagation rate are defined in ASTM D5306 are used. 

High Water-Base Fluids. These water-base fluids have very high fire resistance because as Httle as 5% of the fluid is combustible. Water alone, however, lacks several important quaUties as a hydrauHc fluid. The viscosity is so low that it has Httle value as a sealing fluid water has Httle or no abiHty to prevent wear or reduce friction under boundary-lubrication conditions and water cannot prevent mst. These shortcomings can be alleviated in part by use of suitable additives. Several types of high water-based fluids commercially available are soluble oils, ie, od-in-water emulsions microemulsions tme water solutions, called synthetics and thickened microemulsions. These last have viscosity and performance characteristics similar to other types of hydrauHc fluids. 

Other Fire-Resistant Hydraulic Fluids. Phosphate and more recently polyol esters are marketed as fire-resistant compounds. They are formulated with additives to control wear, oxidation, corrosion, and misting. Seal compatibdity and solvency characteristics of these fluids may be quite different from those of mineral ods. 

Hydraikic fluids are the second largest use of lubricants for automotive and iadustrial markets. Estimates for 1992 are that 1.089 x 10 L(81 x 10 gal) of hydraikic fluids were sold out of 8.9 x 10 L(2.3 x 10 gal) of total iadustrial lubricating fluids. The world market is shown ia Table 6. Most hydraikic fluids were mineral ok-based products. The remainder represented principally fire-resistant hydraikic fluids and synthetic-based lubricants. 

Fire-Resistant Fluids. The total 1992 usage of fhe-resistant fluids amounted to over 151,000 (4 ... 

Except for fire-resistant fluids, synthetic lubricants have not captured a significant portion of the general lubricant or hydrauhc markets, primarily because the cost is two to four times that of other premium lubricants. However, development of satisfactorily formulated products continues. 

Fire-Resistant Hydraulic Fluids. Fire-resistant hydrauhc fluids are used where the fluid could spray or drip from a break or leak onto a source of ignition, eg, a pot of molten metal or a gas flame (17). Conditions such as these exist in die-casting machines or in presses located near furnaces. Specific tests for fire resistance are conducted by Factory Mutual in the United States. 

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