Types of Fire Retardant

In the fourth type of fire retardants, a chemical bond between the molecules of the fire retardant and cellulose should produce a finish that strongly resists the effects of laundering and weathering. Among such retardants may be cited cellulose-ammonium phosphate, cellulose-urea phosphate, cellulose-titanium complexes cellulose-titanium-antimony finishes... 

Another advantage of the amino-resin systems is their applicability to solid wood and wood-composite products. Cedar shingles were the first products treated with this type of fire-retardant system (99, 100, 113, 114). Commercially treated shingles available in the U.S. are based on these systems. Generally, these systems exhibit good durability to outdoor weathering when tested over extended periods (115-17). 

Because of the possible toxic effects of antimony and halogen containing fire retardant polymers in the event of an electrical fire, efforts are now being made to produce fire retardant plastics for the electrical industry, which do not contain these types of fire retardants. 

Effect of Flame Retardants on Combustion Products. There appears to be no documented case of any type of fire retardant contributing to human fire casualties. There is ample evidence that carbon monoxide is the main acute toxicant in flames, although oxygen depletion and other toxic gases may contribute. This topic has been studied intensively (182-185). 

The American Wood-Preservers Association Standards specified the four types of fire-retardant formulations given below (A, B, C, D). Many newer formulations have been developed by commercial enterprises and are proprietary. 

Note that the cost for life years is left out of the equation since the impact on fire is the same between the two types of flame retardants. 

An obvious utility for the type of modeling described is to evaluate the effect of exchanging one material for another in a composite or an assembly or even the addition of a new material, perhaps one of high toxicity but with a low burning rate. It can be used to evaluate the contribution of a material that does not become involved until the later stages of a fire. The model has the potential of assessing the trade-offs of flammability vs. toxicity often encountered with the use of fire retardants. 

Melamine and its salts are widely used in formulations of fire retardant additives, particularly of the intumescent type (4-71. The role played by melamine structures in these additives is however not yet understood. The thermal behaviour is of paramount importance in studies of the fire retardance mechanism. It is known that melamine undergoes progressive condensation on heating with elimination of ammonia and formation of polymeric products named "melam", "melem", "melon" (8.91. The following schematic reaction is reported in the literature (10-121 ... 

This chapter has provided a concise account of an important type of flame retardants based on silicon. This class of flame retardants may provide an opportunity to develop systems for fire retardancy that are environmentally friendly. It seems that there is a growing interest in this type of flame retardant, and this trend most likely will continue, given the increasing concern over the release of the halogenated species into the environment. 

Flame-retardants are used as additives in the preparation of fire retardant paints. They are decomposed by heat to produce nonflammable components, which are able to blanket the flames. Both inorganic and organic types of flame-retardants are available in the market. The most widely used inorganic flame-retardants are aluminum trihydroxide, magnesium hydroxide, boric acid, and their derivatives. These substances have a flame-retardant action mainly because of their endothermic decomposition reaction and their dilution effect. The disadvantage of these solids is that they are effective in very high filler loads (normally above 60 percent). 

In addition to the chemical mechanisms of fire retardants, thermal or barrier-type mechanisms may be operative. Coatings may prevent oxygen from reaching the wood surface. Dilution of combustible gases by noncombustible gases and inhibition of flaming by free radicals can also be in effect. Therefore, fire retardancy of wood involves many complex reactions. The effectiveness of a particular fire retardant depends on the overall summation of these competitive and sequential reactions and the thermal and physical environment of the material. 

Another route to flame-retardant rigid foams is the use of flame-retardant polyether polyols which contain phosphorous and halogen (reactive type). In recent years, due to the fire-gas toxicity caused by halogen-, phosphorous- or nitrogen-containing flame retardants, other types of flame-retardants which do not produce toxic gases are being developed. 

Uses of Fire Retardants in Specific Foam Types... 

Poly(urethane) foams based on polyethers have now largely replaced polydiene rubbers in upholstery and flammability is a major disadvantage compared with traditional upholstery. A major problem is that it is not the fire itself that kills people but the toxic fumes that are produced in the smoke and this is exacerbated by certain types of flame retardant. There are no simple solutions to this problem. Foams in their very nature have a large surface area and a developing fire thrives on the accessibility of fuel from the exposed foam (Chapter 3). The most promising solution is to make the textile fabric surrounding the foam non-flammable so that the fire never reaches the foam itself. 

Ammonium phosphates will act as fire retardants when wood or fabrics are impregnated with them. On heating they evolve ammonia and phosphoric acid. The former retards combustion of the materials and the latter catalyses the charring of cellulose to carbon. The mono ammonium salt can be used in granular form in some types of fire extinguishers. 

These days all products must satisfy application-specific demands on preventative fire protection. Such demands are best fulfilled technically and economically by the use of flame retardants. These help to limit flame spread and heat release in incipient fires and frequently to prevent fires from starting in the first place. The appropriate type of flame retardant material is determined not only by the required flame resistance standard and the physical dimensions for the particular application but also by the family of polymers used. 

This chapter gives the briefest of outlines of the different flame retardant families and their capabilities in protecting plastics compounds. A more comprehensive review of fire ehemistry and the actions of the different types of flame retardant materials is to be found in the previous edition of this Rapra report, Fire - Additives and Materials , Rapra Technology Ltd., 1995. 

This type of extinguisher puts out fires by coating the fuel with a thin layer of fire retardant powder, separating the fuel from the oxygen. The powder also works to interrupt the chemical reaction. 

The most effective fire-retardant polymeric materials are halogen-based polymers (e.g., PVC, chlorinated PVC, polyvinylidene fluoride (PVDF)) and additives (e.g., chlorinated paraffins (CPs), tetrabromobisphenol A (TBBA)). However, the improvement in fire performance depends on the type of fire tests, that is, the application. 

PU foams do not melt in a fire but burn to produce pyrolysis gases, dense smoke and some char. The rate of their burning depends on the type and amount of fire retardant present in the foam. 

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