Chapter 2 - Fire Safety Performance of Flame Retardants Compared with Toxic and Environmental Hazards

Abstract

The case for the use of flame retardants depends ultimately on the overall benefits and costs to society. Flame-retardant systems and additives reduce fire losses, fire injuries, and deaths by reducing the probability of serious fires resulting from exposure to ignition sources of different intensities, and if ignition resistance is overcome, they may also increase the time to rapid fire development and reduce the size of the ultimate fire, thereby increasing the time available for escape and probability of survival for occupants. A wide variety of flame-retardant additive compounds are in use, enabling materials with an otherwise poor fire performance to fulfill regulatory fire performance criteria. This widens the choice and range of applications for different polymers and products, but in many cases an adequate or improved fire performance can be obtained either by alternative materials or systems that do not require flame-retardant additives or by the use of alternative flame-retardant systems. Different individual flame-retardant additives and systems vary in terms of their durability in normal use, the extent to which they are released to the environment, their subsequent bioavailability, and their toxicity. They also vary in their fire performance and in terms of the toxic and environmental hazards from their combustion products when they are burned. The yields of toxic combustion products in fires depend on the elemental composition, the organic structure, and the combustion conditions under which the fuel is decomposed. Flame retardancy of polymers is often achieved by the addition of compounds containing elements such as halogens, nitrogen, or phosphorus, so that the combustion products then include toxic compounds containing these elements, such as acid gases, organic compounds containing phosphorus, hydrogen cyanide, and environmental toxins such as halogenated dibenzodioxins and furans. Combustion products from all polymeric materials also contain a complex mixture of toxic carbon compounds. The yields of these products highly depend on the combustion conditions, in terms of nonflaming or flaming behavior, and for flaming combustion, the fuel/air equivalence ratio and temperature, while for flame-retardant polymers the additive chemistry also has an influence. Other methods for achieving a good standard of fire performance may involve noncombustible (inert) fillers or barriers, or additives that release water, promote char formation, or otherwise inhibit combustion of a material or composite system. These issues are considered in relation to the development of “greener” systems for achieving flame retardancy while minimizing toxic products and environmental hazards.