The overall toxicity of polyurethane materials followed a similar trend to their HCN yields; with flexible foams generally being the least toxic, rigid foams being slightly more toxic and polyisocyanurate foams being the most toxic. The three-compartment test consisted of a 2.43.72.4m burn room, a 2.44.62.4m corridor and a 2.43.72.4m target room where samples would be taken. It is inexpensive and easy to install, however, it is a severe fire risk and requires a thermal barrier to make it safe. Alongside this, the decomposition of the foam into an amine, alkene and carbon dioxide was also proposed. The toxic effect of carbon monoxide is characterised by a lowered oxygen-delivery capacity of the blood, even when the partial pressure of oxygen and the rate of blood flow are normal. Open Access This article is distributed under the terms of the Creative Commons Attribution 4.0 International License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. Secondary air is added in a mixing chamber to give a total gas flow of 50Lmin1. This is due to the large range of available fire retardants found in polyurethane foams, which suggests that the toxicity will likely follow the general trends in the literature for all materials regarding fire retardants. In a 12-square-foot area, urethane was totally burned off, but the rest suffered more minor damage. The methods of assessment of fire toxicity are outlined in order to understand how the fire toxicity of polyurethane foams may be quantified. In particular, the ventilation condition has a critical effect on the yield of the two major asphyxiants, carbon monoxide and hydrogen cyanide. The results of these experiments and the mechanism of decomposition derived correlated well with work by Rein et al. The yields of CO and HCN from five bench-scale methods have been compared to large-scale data under a range of flaming fire conditions (Stec & Hull 2014). 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. The two main market uses for polyurethane are in the furniture and interior industry and the construction industry with 28% and 25% of the market, respectively (Markets & Markets report 2011). This prompted the authors to perform further studies in order to understand why allowing the foam to smoulder increased the yield of HCN during flaming combustion. Bench-scale methods used for generating toxic effluents from polyurethane foams have met with controversy. 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. The authors acknowledged that they did not include isocyanates in their calculations. In another investigation, using a steady state tube furnace, Blomqvist et al. J Allergy Clin Immunol 104:p341347, Woolley WD, Fardell PJ (1977) The prediction of combustion products. It gives off toxic gasses and smoke, which makes it difficult to evacuate and put out a fire. FEC model from ISO 13571. Fire Res 1:p1121. The Steady state tube furnace apparatus, ISO/TS 19700. During these tests, the PIR was set up as wall panels covered on two faces with aluminium foil. It forces combustion by driving the sample into a furnace of increasing heat flux at a fixed rate, so that, by running several tests with the same material with different ventilation conditions, each fire stage can be replicated by steady state burning. The chemistry of polyurethane foams and their thermal decomposition are discussed in order to assess the relationship between the chemical and physical composition of the foam and the toxic products generated during their decomposition. Rigid MDI based foams are primarily used for insulation in the construction industryand can also be found in the transport industry. Since 2004, by law, the U.S. requires all mattresses to be fireproof to a specific temperature point and ever since the toxicity levels in foam memory mattresses have increased. One analysis of fire victims' blood showed a trend of declining COHb and a rise in cyanide concentrations (Anderson et al. This will result in a HCN yield related that specific furnace temperature. Fire Safety Science Proceedings of the ninth international symposium. The uptake, distribution, metabolism and excretion of cyanide is much more complex than for CO and quantifying CN- in fire victims is more expensive and not routinely undertaken. The authors reported GC/MS analysis of the condensed phase products obtained. National Fire Protection Association, 82, p 161, Vilar WD (2002) Chemistry and Technology of Polyurethanes - Chapter 1. 13) (UK Fire Statistics 2013). The steady state tube furnace (ISO/TS 19700 2013), shown in Fig. For any larger fire there will always be a significant yield of CO, HCN (from nitrogen containing materials), hydrocarbons and smoke. The resulting substituted urea can then react with another isocyanate to produce a biuret linkage (Scheme4). These nucleophiles include amines, alcohols, carboxylic acids, thiols, water, ureas and urethanes (Aneja 2002). volume5, Articlenumber:3 (2016) Aromatic diisocyanates ortho- or para- to one another will have an activating effect on each other, thus increasing their reactivity. Fire Technology 51:p318, Blomqvist P, Lonnermark A (2001) Characterization of the combustion products in large-scale fire tests: comparison of three experimental configurations. Combustion and Flame 146(12):p95108, Rogaume T, Bustamante-Valencia L, Guillaume E, Richard F, Luche J, Rein G, Torero JL (2011) Development of the Thermal Decomposition Mechanism of Polyether Polyurethane Foam Using Both Condensed and Gas-Phase Release Data. Toxic product yield data from the smoke density chamber (ISO 56592 2012), the controlled atmosphere cone calorimeter (based on ISO 56601 2002), the fire propagation apparatus (FPA) (ASTM E 2058), the French railway test (NFX) (NF X 70100 2006), and the steady state tube furnace (SSTF) (ISO/TS 19700 2013) were compared to published large-scale enclosure fire data (from a standard ISO 9705 room) for two polymers, polypropylene (PP) and polyamide 6.6 (PA 6.6). The difference with other polyurethane foams is that memory foam also contains added chemicals that increase its viscosity and elasticity, hence its alternate name, viscoelastic foam. VOCs have the ability to vaporize, or off-gas, at room temperature. Fire and Materials 23:p171185, Hull TR, Paul KT (2007) Bench-scale assessment of combustion toxicity-A critical analysis of current protocols. 4). The polyisocyanurate, on the other hand, produced slightly more HCN than the rigid foam (17mgg1 vs 12mgg1). The first is by combination with the ferric ion in mitochondrial cytochrome oxidase, preventing electron transport in the cytochrome system and inhibiting the use of oxygen by the cells. UPDATED 8/16/2011 The Massachusetts Division of Fire Safety (DFS) is investigating the causes of three house fires that were ignited while insulation contractors were installing spray polyurethane foam. This suggests that any amines formed would have reacted with isocyanates in the vapour phase to form ureas, some of which would have condensed to produce the observed waxy white substance. Equation The authors acknowledged that the lower nitrogen recovery fraction for the flexible foam could be due to fuel nitrogen being lost as isocyanates, which are known to escape into the effluent plume, while for rigid foams they are more likely to be trapped in the burning solid (Woolley & Fardell 1977). The polyurethane market was estimated to be worth $33 billion in 2010 and is expected to continue to grow to over $55 billion by 2016. The yields of some of the most toxic gases from unwanted fires (such as CO, HCN and some organic irritants) have been demonstrated to be directly related to the combustion conditions (Purser 2002). 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 (). National Fire Protection Association, Quincy MA, USA, pp 296, Purser DA, Purser JA (2008a) HCN yields and fate of fuel nitrogen for materials under different combustion conditions in the ISO 19700 tube furnace. The initial decomposition of the foam, at >300C, results in the volatilisation of isocyanates, amines and Woolleys yellow smoke, leaving behind polyols in the condensed phase. Additionally, the amount of CO generated for both materials began to taper off at 1.2-2.0 as the available oxygen becomes so low that the generation of CO becomes limited, while the yield of HCN continues to increase with equivalence ratio and temperature. Instead polyureas were detected in the vapour phase and also in the condensed phase as a waxy, insoluble white substance. depends on the mass loss rate of the specimen and the available air; for most methods one or both are unknown; will be increased by an unknown factor if products are recirculated into the flame zone. 6). P.J. The trimerisation results in a highly stable isocyanurate ring which confer additional thermalstability to polyisocyanurates (Scheme7). National Fire Protection Association, Quincy, MA, pp 5482, Guo X, Wanga L, Zhanga L, Lia S, Hao J (2014) Nitrogenous emissions from the catalytic pyrolysis of waste rigid polyurethane foam. Woolley et al. The protocol has been modified as a toxicity test by the mass transport industries, in the aircraft (EN 2826 2011), maritime (Fire Test Procedure Code 2010), and railway tests (CEN/TS 455452 2009). In addition, asphyxiation can also occur as a result of lowered oxygen concentration, and is affected by the carbon dioxide concentration. STM wrote the manuscript and produced all of the images used in figures. The FED value is calculated using the exposed dose relationship (concentration-time product, Ct) for CO. . There are two reasons for this: The yields of the major toxic products (carbon monoxide (CO) and hydrogen cyanide (HCN)from N containing materials) will be much greater. Part of The use of 13C labelling in this case allowed the authors to confirm that the nitrogenous compounds, HCN and organonitriles, originated from the thermal fission of the aromatic rings with the nitrile carbon being the 2-,4- or 6- carbon of the MDI ring. Interflam Conference Proceedings. (1985) when a flexible polyurethane foam was first heated at a temperature below its auto-ignition temperature, followed by flaming combustion of the remaining char and residue at a higher temperature. Ann occup Hyg 19:269273, Levchik SV, Weil ED (2004) Thermal Decomposition, combustion and fire-retardancy of polyurethanes - a review of the recent literature. An equivalence ratio of 0.5 represents a well-ventilated scenario, typical of an early growing fire, while a ratio of 2 corresponds to the under-ventilated stage responsible for high yields of toxic effluents. (1972) noted that the yellow smoke was produced up to around 600C, where it would then decompose to give a family of low molecular weight, nitrogen containing products including hydrogen cyanide, acetonitrile, acrylonitrile, pyridine, and benzonitrile. (2007)), the sample is raised to a fixed furnace temperature, which is further increased in the gas phase during flaming combustion. According to Tim Rodrique, the director of the DFS, investigators suspect that the fires were caused by the exothermic reaction that results from the mixing of the two chemicals used to make . The half-scale ISO 9705 experiments showed a wider range of ventilation conditions up to ~2.0. The authors acknowledged that further investigation of the steady state tube furnace was warranted as in some of the testing they suspected an instrumental error, since they were unable to account for roughly two-thirds of the total carbon from the sample and detected unusually low levels of CO2 during the under-ventilated tests. Using a cup furnace with a 200L sampling chamber (identical in design to the one used in the smoke chamber experiments), a 3.88g sample of foam was heated to just below its ignition temperature (370C) which yielded <1mgg1 HCN. The presence of both amines and water in the decomposition products of polyurethane foams are discussed in later sections. This shows that the reactions of isocyanates are much faster with amines and slower with carboxylic acids, urethanes and amides than for the alcohols used in polyurethane production. April 30, 2021 April 16, 2021 by Shobita Ravichandran. These yields are comparable to that of the results reported by Blomqvist et al. MDI is a diaromatic diisocyanate compound that boils at 208C and is primarily used in the production of rigid foams. Work by Guo et al. CO and HCN are the main asphyxiants produced during the combustion of polyurethanes and there have been a large number of studies published regarding their yields. National Bureau of Standards, Gaithersburg, MD, Levin BC, Paabo M, Birky MM (1983b) Interlaboratory evaluation of the 1980 version of the national bureau of standards test method for assessing the acute inhalation toxicity of combustion products, NBSIR 832678, National Bureau of Standards, Gaithersberg, MD, Levin BC, Paabo M, Fultz ML, Bailey CS (1985) Generation of Hydrogen Cyanide from Flexible Polyurethane Foam Decomposed under Different Combustion Conditions. Material composition, temperature and oxygen concentration are normally the most important. Polyurethane foam, when burnt, gives off: Sulfuric acid Cyanide gas Ethane Phosphine. National Bureau of Standards, Washington D.C. Levin BC, Paabo M, Fultz ML, Bailey C, Yin W, Harris SE (1983a) Acute inhalation toxicological evaluation of combustion products from fire-retarded and non-fire retarded flexible polyurethane foam and polyester. Despite their name, the term polyurethane is used to describe a family of polymers whose monomers are joined by a range of functional groups primarily derived from the polyaddition of polyisocyanates and polyalcohols. 4)). The authors declare that they have no competing interests. The strain of two electronegative atoms (N and O) results in electron density being pulled away from the carbon atom, giving it a strong partial positive charge. Thermal decomposition of polyurethanes is usually the reverse of polymerisation, resulting in the formation their precursor functional compoundsdiisocyanates, diamines and dihydroxy compounds. It is generally accepted that the thermal decomposition occurring during flaming combustion is best represented by the thermal decomposition of a material in an inert atmosphere. CO yields are generally very low for well-ventilated conditions (in the absence of halogens) but increase considerably under-ventilated combustion conditions. 10. A more recent review, by Levchik and Weil (2004), assessed the decomposition, combustion and fire-retardancy of polyurethanes. A comprehensive review of fire retardants and their use in polyurethane foams was published by Singh and Jain (2009). Isocyanates also react with themselves in various ways to produce dimers, trimers and completely new functional groups. The general approach, described in ISO 13571 (2012), is to ensure that the available safe escape time (ASET) before escape routes become obscured by smoke and/or filled with toxic gases, exceeds the required safe escape time (RSET). Foams Under Laboratory Conditions, Fire Research Note, No 1039. At a CO concentration of 10 ppm, impairment of judgement and visual perception occur; exposure to 100 ppm causes dizziness, headache, and weariness; loss of consciousness occurs at 250 ppm; and 1000 ppm results in rapid death. However, the presence of Cu2O reduced the HCN generated by the flexible polyurethane foam by 70-90% at low temperatures. The main toxic combustion products can be divided into two classes: asphyxiant gases, which prevent oxygen uptake by cells, with loss of consciousness and ultimately death; and irritant gases which cause immediate incapacitation, mainly by effects on the eyes and upper respiratory tract, and longer term damage deeper in the lung. Insulation, like all building products, has an 'embodied' carbon footprint resulting from energy use during the manufacturing process. This char can decompose further, leaving behind a residue at >800C, to produce simple organic fragments and some polycyclic aromatic hydrocarbons (PAHs). 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 revised protocol is based on continuous sampling of the fire effluent. The reaction of a urethane with another isocyanate will produce an allophanate (Scheme5). I recently purchased a memory foam (polyurethane) mattress and was looking online to see how long they take to "air out". Sub-ambient differential distillation of the remaining residue yielded a range of short-chain aldehydes (such as formaldehyde and acetaldehyde), ketones, alkenes and high molar mass polyol fragments. In 1975, California passed flammability standards known as Technical Bulletin 117 (TB117), which required polyurethane foam and fabrics produced in state to be treated with flame-retardant chemicals . The results showed a HCN yield of 15.8mgg1 at 600C. Similarly, Busker et al. This is true of ALL polyurethane foam since it is an organic material, just like wood or cotton fabric. Flaming combustion of the polyurethane foam did not cause any animal deaths, however the non-flaming combustion resulted in deaths post-exposure. Stec and Hull (2011) presented material-LC50 data for rigid polyurethane foam and polyisocyanurate foam, calculated using rat lethality data from ISO 13344 (1996). While the link between CO yield and equivalence ratio is well established, the yield of HCN in ventilation limited conditions shows more complicated behaviour for polyurethanes. Each of the decomposition steps took place at a lower temperature in air than in nitrogen, which further suggests the direct interaction of oxygen with the foam during decomposition. Critical Reviews in Toxicology 32(4):259, Article (2011) developed a mechanism based on both condensed and gas-phase decomposition in air. Polyurethane foam insulation is a superior insulator with high RValue. Primarily, isocyanates react with alcohols to produce urethane linkages in the polymer (Scheme1). In particular, the ventilation condition has a . The findings from these studies demonstrated that yields of different toxic products are highly dependent on equivalence ratio (either positively or negatively correlated), and elemental and molecular composition of the material. The authors acknowledged the complexity of the decomposition of the material but were able to summarise it effectively in a 5-step mechanism (Fig. Rigid polyurethanes primarily produced aromatic compounds in the condensed phase products of decomposition, whereas flexible polyurethanes produced aromatics, alcohols, aldehydes and heterocycles. Fire Research Notes 951:p117. 1995). The average well-ventilated yield of HCN was found to be 4mgg1, while it was 9mgg1 for under-ventilated conditions. Common polyurethane functional groups i) urethane ii) urea iii) carbodiimide iv) uretdione v) isocyanurate. Recent work by Allan et al. The full size ISO 9705 test resulted in well-ventilated flaming ( 0.260.5) due to the relatively large volume of air and relatively small sample size. 1 The reported yields for the tests performed can be found in Table8. The fire department was not immediately called, so the oil burned completely. Polymer International 53:p15851610. The smoke density chamber (ISO 5659-2) showing a sampling probe for fire smoke toxicity. Biurets are the result of the reaction of isocyanates with substituted-urea functional groups and allophanates are formed in small amounts (unless catalysed) by the reaction of isocyanates with urethanes. Fire Safety Journal 42:p340365, ISO 12136 (2011) Reaction to fire tests Measurement of material properties using a fire propagation apparatus, ISO 13344 (1996) Estimation of lethal toxic potency of fire effluents, ISO 13571 (2012) Life-threatening components of fire-Guidelines for the estimation of time available for escape using fire data. Busker RW, Hammer AH, Kuijpers WC, Poot CAJ, Bergers WWA, Bruijnzeel, PLB (1999) Toxicity testing of combustion products of polyurethane and polyvinylchloride. TRH wrote the fire toxicity section of the manuscript. TDI is produced as the 2,4- and the 2,6- isomer which have a boiling point of 121C and 120C respectively. Equation However, during the combustion of polyurethane foams, the HCN yield is notably higher when the fire progresses from smouldering to flaming combustion. The transport industries have adopted the smoke density chamber (SDC) ISO 56592 (2012) and ASTM E662, for quantification of toxic product yields (Fire Test Procedure Code 2010; CEN/TS 455452 2009) using simple pass/fail chemical detection (e.g. The authors compiled toxicological data from a range of primary online databases and also requests were made to collect unpublished data that were not publically available. al, 2014). The NFX generates data intermediate between the well-ventilated and under-ventilated fire conditions. The reaction of a urethane with another isocyanate will produce an allophanate (Scheme 5). Additionally, assorted nitrogenous organics were detected in the tar including aniline, quinoline, pyridine, benzonitrile, indole and acridine derivatives with more than 50% of the tar nitrogen being bound as 4-[(4-aminophenyl)methyl]aniline (the amino analogue of MDI). At sufficiently high concentrations, or when attached to submicron particles, such as soot, most irritants can penetrate deeper into the lungs, causing pulmonary irritation effects which may cause post-exposure respiratory distress and death, generally occurring from a few hours to several days after exposure, due to pulmonary oedema (flooding of the lungs) (ISO 13571 2007). Apparatus where changes rapidly allow little time for sampling and measurement of mass loss and effluent compositionat a specific value of, with resultant errors and uncertainties. The Purser model, presented in equation1, uses \( {\mathrm{V}}_{{\mathrm{CO}}_2} \) a multiplication factor for CO2 driven by hyperventilation, therefore increasing the FED contribution from all the toxic species, and incorporates an acidosis factor A to account for toxicity of CO2 in its own right (ISO 13344 1996). Heating of polyurethane foam while working on pipes Heating MDI-based glues Soldering Treatment with a heat gun Cutting with torches or hot wire Hot scissors Grinding Sawing It has been estimated that non-flaming thermal degradation of some polyurethane products may begin as low as about 150C (300F) to . CEN/TS 455452 (2009) Railway applications - Fire protection on railway vehicles Part 2: Requirements for fire behaviour of materials and components, Chambers J, Jiricny J, Reese CB (1981) The Thermal Decomposition of Polyurethanes and Polyisocyanurates. Two mechanisms have been identified for the toxic effects of cyanide. Over this period there was a corresponding shift from the main cause of death in fires being attributed to burns to being attributed to inhalation of smoke and toxic gases. Additionally, the self-addition of isocyanates to produce isocyanurates (v in Fig. However, due to the poor reproducibility of smoke chamber experiments, the tendency for it to give very low HCN yields, and the fact that the experiment is well-ventilated, the reported toxicity is likely much lower than in a real fire situation. In most countries, there are no regulations covering the fire toxicity of building components, or for most road vehicles, including goods vehicles in tunnels. Isocyanates should be considered when assessing the fire toxicity of polyurethane foams, due to their acute irritating effects and chronic effects associated with exposure. HCN, in particular, contributes significantly to the overall fire toxicity of polyurethane foams. Anderson RC, Croce PA, Feeley FG, Sakura JD (1983) Study to assess the feasibility of incorporating combustion toxicity requirements into building materials and furnishing codes of New York State: Final report, vol I, II, III, Arthur D. Little, Inc. Report, Reference 88712, May 1983. Additionally, NO was detected during the well-ventilated tests and NH3 during the under-ventilated tests. STM would like to acknowledge the University of Central Lancashire for provision of a studentship. (1990) also reported increased HCN yields when the sample was allowed to smoulder before flaming in similar apparatus as above. Off-gassing is the unpleasant odor caused by volatile . Manage cookies/Do not sell my data we use in the preference centre. The FED is expressed as the sum of contributions to toxicity from individual species and normalised to 1g of fuel in 200L fire effluent, as used in BS 6853 (1999). During flaming combustion of polyurethane foams, the yield of toxicants can be directly related to the fuel/air ratio, expressed as an equivalence ratio (). 1982), and a three . However, from a fire toxicity perspective it is generally assumed that heat and other gases will have already prevented survival, while other toxicants such as CO or HCN, will be present in lethal quantities further from the fire where the oxygen depletion would not be considered harmful. As with all foams, memory foam compresses under pressure. 8-80, addressing . In contrast to the relativelywell-defined effects of asphyxiants, the effects of exposure to irritants are more complex. For the purpose of estimating toxicity in fires, fire growth has been classified into a number of stages (ISO 19706 2011): Although on some occasions smouldering (oxidative pyrolysis) can generate toxicologically significant quantities of effluent (for example smouldering cotton, or polyurethane foam), typicallythe rate of reaction, and hence the amount of toxic species generated will be small, so it is unlikely to affect anyone outside the immediate vicinity. 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. 3 While limited data were available regarding the flaming combustion of rigid polyurethane foams, the results were of a similar scale to those presented by Stec and Hull (2011). Those with constant combustion conditions are more suited to producing data suitable for comparison and modelling: the steady state tube furnace (SSTF) (ISO/TS 19700 2013) has been specifically designed to achieve this. Memory foam is a type of polyurethane foam. The authors tested a rigid polyurethane foam using a NBS cup furnace (as described in Levin et al. However, it does suggest that yield of toxic products is effected by covering the foam with another material during flaming combustion. 95% of the demand for polyurethanes is situated in North America, Asian-pacific, and European markets; with demand expected to increase in Eastern Europe and South America in the next 1015 years. In a report from the same laboratory, Braun et al. Their apparently transient nature results from their very high reactivity with amines and their fairly high reactivity with water (which is almost always present in fire effluent). Polymer Degradation and Stability 93:p20582065, Tewarson A (2002) SFPE Handbook of Fire Protection Engineering, 3rd ed. Substituted ureas decompose between 235 and 250C and carbodiimides decompose between 250 and 280C. Refer to MSDS. Journal of Analytical and Applied pyrolysis 113:p202215, Gharehbagh A, Ahmadi Z (2012) Chapter 6: Polyurethane Flexible Foam Fire Behaviour, Polyurethane. Global usage is expected to expand from 13.65 Mt in 2010 to 17.95 Mt by 2016. Experimental data reported a 28% recovery of DAT which supports the proposed decomposition mechanism. (1999) tested both rigid and flexible polyurethane foams using a bespoke smoke chamber apparatus to assess the toxicity of the flaming combustion products of the materials to rats. 2008) and is 40kWm2 in the centre of the furnace at 650C and 78kWm2 at 825C. Fire and Materials 31:p327354, Schnipper L, Smith-Hansen ES (1995) Reduced combustion efficiency of chlorinated compounds, resulting in higher yields of carbon monoxide. 1982), the authors exposed male Fisher 344 rats in a 200L exposure chamber to the fire effluent from the flaming and non-flaming combustion of both materials. 5). Hydrogen cyanide is approximately 25 times more toxic than carbon monoxide through the formation of the cyanide ion, which is formed by hydrolysis in the blood (Hartzell 1993). 2 Other fire retardants such as melamine are reported to significantly increase the HCN yield of polyurethane foams. Polystyrene (EPS and XPS) has significant amounts of styrene offgassing early in life. (2006) and also Garrido and Font (2015). Early work by Woolley et al (1975) indicated that the decomposition of polyurethanes up to around 600C resulted in the volatilisation of fragmented polyurethane and subsequent release into a nitrogen rich yellow smoke, containing partially polymerised isocyanates and droplets of isocyanate from the foam. The relation of the FED to the material-LC50 is given in equation4. This range of functional groups and their ratios in the polymer are a large contributing factor to the wide range of properties that polyurethane materials can possess. 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.