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The yields of acid gases and nitrogen-containing products depend upon the proportion of the appropriate elements in the materials burned and the efficiency of conversion. Polyurethane is made when methylene diphenyl diisocyanate (MDI) and toluene diisocyanate (TDI) react with polyols. For example, Levin and coworkers reported that melamine-treated flexible polyurethane foam generated 6 times more HCN than an equal amount of non-melamine treated foam. In the case of flaming combustion, one of the most important factors relating to the toxic product yield is the fuel/air ratio which, as defined earlier, can be expressed as an equivalence ratio (ϕ). More recent studies have supported and expanded upon the aforementioned thermal decomposition mechanisms of polyurethane foams. (2007). Some of these methods attempt to address the transition through the fire stages by monitoring the formation of toxic gases as a function of time, as the oxygen concentration falls, and the fire condition changes from well-ventilated to under-ventilated. It is therefore essential to the assessment of toxic hazard from fire that each fire stage can be adequately replicated, and preferably the individual fire stages treated separately. Is Thermoset Polyurethane Foam Toxic? These fires are large, relative to the enclosure, and produce greater volumes of effluent, affecting occupants over a much wider part of any building. Therefore the contribution of HCN to fire deaths is difficult to assess, and analysis for CN− is limited to cases where lethal concentrations of CO are absent. The toxic hazards associated with fire and the inability of victims to escape from fire atmospheres may be considered in terms of major hazard factors: heat, smoke and toxic combustion products (Hartzell 1993). ISO 19706 (2011) Guidelines for assessing the fire threat to people. The significant increased yields at 1000 °C and 1200 °C could also be attributed to pyrolysis of the nitrogenous combustion products into HCN due to the low air flow rate. Diisocyanates react with polyols to produce the flexible memory foam. This is especially true for infants that sleeping on a new mattress. The use of 13C labelling by Chambers et al. Their development continued commercially in Germany, eventually leading to a global multibillion dollar industry (Vilar 2002). Fire Technology 51:p213–217, Blais M, Carpenter K (2015) Flexible Polyurethane Foams: A comparative measurement of toxic vapors and other toxic emissions in controlled combustion environments of foams with and without fire retardants. (2013) further supported the presence of two separate decomposition mechanisms for flexible foams. The reaction of an isocyanate functional group with water (Scheme 2) results in the formation of an unstable carbamic acid group, which in turn decomposes to release an amine and carbon dioxide. Keywords: Fire, Combustion, Toxic, Toxicity, Polyurethane, Foam, Decomposition, Asphyxiant, Cyanide, HCN Introduction Polyurethanes are a diverse family of synthetic polymers that were first synthesised in 1937 by Otto Bayer. Additionally, aromatic isocyanates with more steric hindrance are likely to be less reactive (such as the 2 position in 2,4-TDI (Fig. The toxic product generation during flaming combustion of polyurethane foams is reviewed, in order to relate the yields of toxic products and the overall fire toxicity to the fire conditions. And if that alone isn’t bad enough they are carcinogenic to humans. Toxicology 115:7, Henneken H, Vogel M, Karst U (2007) Determination of airborne isocyanates. The main asphyxiants, carbon monoxide and hydrogen cyanide have been widely studied and are the best understood (ISO 13571 2007). Rigid Polyurethane Foam Products. Table 1 shows the relative reactivity of isocyanates with nucleophiles at 25 °C without the presence of a catalyst. The mechanisms of decomposition are well understood and the decomposition products of both rigid and flexible polyurethane foams are very similar at high temperatures. The second results in a brief stimulation, followed by severe depression, of respiratory frequency, also starving the body of oxygen, and causing convulsions, respiratory arrest and death (Alarie 2002). Historically, material-LC50 data has been reported directly based on animal lethality testing, however due to the declining use of animal testing in fire toxicity assessment, calculations based on standard lethality data (such as ISO 13344 1996) are more commonly used. Bench-scale methods used for generation of toxic fire effluents ideally should be capable of reproducing individual fire stages or combustion conditions, for input into models of combustion toxicity. The highest concentration these compounds were formed at occurred at a decomposition temperature of 350–400 °C which indicated no new degradation steps had occurred beyond 350 °C. At lower temperatures, decomposition differs, depending on the composition and physical properties of the polymer, although clear trends can be identified. (1991b) wherein polyurethane containing a phosphate fire retardant caused immediate death of all of the animals. However, when this type of foam contained a reactive phosphate fire retardant, the combustion products caused grand mal seizures and death in rats. In many studies (such as those by Stec and Hull (2011), Purser and Purser (2008a) and Blomqvist et al. Journal of Fire Sciences 8:p63–79, BS 6853 (1999) Code of practise for fire precautions in the design and construction of passenger carrying trains. (1972). Alongside this, the decomposition of the foam into an amine, alkene and carbon dioxide was also proposed. TNO Report. 3 (1999) used the controlled atmosphere cone calorimeter, but argues correctly, in the authors' opinion, that an instantaneous “effective” global equivalence ratio ϕ Material composition, temperature and oxygen concentration are normally the most important. The heating of polyurethanes in an inert-atmosphere results in the progressive rupturing of bonds as a function of temperature. We are having a polyurethane insulation applied to our roof. Similarly, well-ventilated fires are generally small, and of low toxicity. Since HCN is a major contributor to the fire toxicity of polyurethane foams, the mechanisms by which they decompose are vital in understanding why they produce large-quantities of HCN during under-ventilated burning. The fire toxicity of a material can also be expressed as a material-LC50, which in this case is the specimen mass M of a burning polymeric material which would yield an FED equal to one within a volume of 1 m3. When ϕ = 1 the theoretical amount of air is available for complete combustion to carbon dioxide (CO2) and water. This agrees with the fact that oxidation of NH3 and HCN to NO (and NO2, although it was not analysed in these experiments) would occur more readily during well-ventilated burning. Elemental analysis of the polymers showed that the CMHR-FPUR contained 8.22 % nitrogen by weight and the PIR contained 6.15 % nitrogen by weight. Therefore, the products of decomposition can be predicted from the composition of the polymer. 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