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. They attributed the different decomposition mechanisms to the physical form of the polyurethane foam, rather than to any chemical differences. 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 steady state tube furnace produced a CO yield that was closer to what would be expected for under-ventilated conditions. The chemical additives to the polyurethane are said to give off a distinct chemical odor that lessens after adequate ventilation. Most polyurethanes are cross-linked to some degree and decompose without melting. Taking into consideration the issues with repeatability of large-scale testing, the authors asserted that the similar trend in HCN yields supported the good relationship between the tube-furnace and large-scale results. The higher flammability of these new furniture products took people by surprise, and has been blamed for an increased number of serious fires and a tripling of fire deaths over 20years (Fig. These VOCs come mainly from the polyurethane used in the mattress, but also from other chemicals used in flame retardants and plastics, the researchers said. Isocyanates are a highly reactive family of compounds that are characterised by the RN=C=O functional group (where R can be any aliphatic or aromatic functionality). Google Scholar, Allan D, Daly J, Liggat JJ (2013) Thermal volatilisation analysis of TDI-based flexible polyurethane foam. Nitrogen dioxide dissolves rapidly in water to form nitric and nitrous acid. Vilar Consultoria Tcnica Ltda, Rio de Janeiro, Voorhees J (1975) Extreme Toxicity from Combustion Products of Fire-Retarded Polyurethane Foam. Provided by the Springer Nature SharedIt content-sharing initiative. (1969) reported the decomposition of rigid polyurethane foams in both nitrogen and air to assess the production of CO, HCN and NH3. Carbon monoxide binds to the haemoglobin in red blood cells resulting in the formation of carboxyhaemoglobin (COHb), with stability 200 times greater than that of oxyhaemoglobin, impeding the transport of oxygen from the lungs to the cells in the body. volume5, Articlenumber:3 (2016) Centre for Fire and Hazard Science, University of Central Lancashire, Preston, PR1 2HE, UK, Sean Thomas McKenna&Terence Richard Hull, You can also search for this author in 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. Only the SSTF has a heated reaction zone which replicates the hot layer. Very few authors have assessed the yields of isocyanates produced during the flaming combustion of polyurethane foams and as such there is a limited amount of data available. Aromatic diisocyanates ortho- or para- to one another will have an activating effect on each other, thus increasing their reactivity. CO also combines with myoglobin in the muscle cells, impairing diffusion of oxygen to cardiac and skeletal muscles (Purser 2008b). Bulky substituents that impinge on the isocyanate group can reduce its reactivity. In addition, asphyxiation can also occur as a result of lowered oxygen concentration, and is affected by the carbon dioxide concentration. EN 2826. False True. (P.J. The first step is the decomposition of the urethane bonds to release and volatilise isocyanates up to 300C, with long chain alcohols being left behind in the condensed phase, followed by the alcohols degrading at around 400C. These nucleophiles include amines, alcohols, carboxylic acids, thiols, water, ureas and urethanes (Aneja 2002). The authors acknowledged that they did not include isocyanates in their calculations. At 650C, the yield of HCN from the CMHR-PUF increased up to ~2.0 where it reached a peak of 14mg of HCN per gram of polymer burned. 12, feeds the sample (typically around 25g of pellets or granules) into its hot zone at a fixed rate, under a controlled air supply, inside a horizontal silica tube of diameter 48mm, allowing adequate mixing of fuel and oxidant. National Fire Protection Association, Quincy, pp 283, Purser DA (2007) The application of exposure concentration and dose to evaluation of effects of irritants as components of fire hazard. 2012). As the availability of oxygen becomes lower in proportion to the amount of fuel, the yields of certain toxic gases will increase. In a series of investigations, Purser and Purser (2008a) examined the yields of HCN from a range of materials and the conversion of fuel nitrogen to HCN. (2007) assessed the toxic product yields of a flexible polyurethane foam that was designed for use in hospital mattresses. The polyisocyanurate, on the other hand, produced slightly more HCN than the rigid foam (17mgg1 vs 12mgg1). As a result of this, studies that use ventilation controlled conditions, such as those using the steady state tube furnace (ISO/TS 19700 2013), are more likely to give a realistic representation of these reduced oxygen environment fire conditions. The reaction of a urethane with another isocyanate will produce an allophanate (Scheme5). 2012). However, when the TDI was unable to enter the pyrolysis zone, the slower, irreversible decomposition to diaminotoluene (DAT) would occur. Science 187:p742744, Wisnewski AV, Lemus R, Karol MH, Redlich CA (1999) Isocyanate-conjugated human lung epithelial cell proteins: A link between exposure and asthma? An FED equal to one indicates that the sum of concentrations of individual species will be lethal to 50% of the population over a 30min exposure. Polyurethanes are named from the presence of theurethane (also known as carbamate) functional group (Fig. Polyurethane foam, when burnt, gives off: Sulfuric acid Cyanide gas Ethane Phosphine. The increased yield of HCN for the CMHR-FPUR between 650C and 850C is likely due to the increased fragmentation of nitrogenous organic compounds in the flame, similar to the behaviour during non-flaming combustion in air reported by Woolley et al. (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. 1982), a developmental method (SwRI/NIST method) which used a radiant heater on the sample which lead into a 200 L exposure chamber, a cone calorimeter (ISO 5660 2002), a furniture calorimeter (as described in Babrauskas et al. True. This causes deterioration in mental and muscular performance. Using polyurethane indoors can expose you to fumes with a number of potential side effects. Isocyanurate rings are the most thermally stable in an inert atmosphere and decompose between 270 and 300C. However, while the char produced when the polymer was heated at 370C contained only 20% of the total nitrogen from the polymer, 40% of that (8% of the total nitrogen in the polymer) was recovered as HCN when the char was burned at 600C. Woolley WD, Fardell PJ, Buckland IG (1975) The Thermal Decomposition Products of Rigid Polyurethane. Similarly, Busker et al. Further to this, a similar pattern began to emerge in the injuries of fire victims (Fig. 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. In particular, the ventilation condition has a . Fire Safety Journal 7:p11, Kavanagh BP, Pearl RG (1995) Inhaled nitric oxide in anesthesia and critical care medicine. This amine may then undergo further reaction with other isocyanates present to produce a urea (Scheme3). TNO Prins Maurits Laboratory, The Netherlands. Similarly to the trend reported by Stec and Hull (2011) in well-ventilated conditions, this can be attributed to gas phase free radical quenching in the material by the chlorine present in both the CMHR-PUF and PIR (2.53% and 3.56% chlorine by weight, respectively). The authors noted no significant difference in the range of yields of isocyanates detected in either well- or under-ventilated conditions with a range of 1.0-1.6mgg1. TDI is primarily used in the production of flexible foams, which are used in the furniture and interior industries. The radiant heat apparatus, smoke chamber and controlled atmosphere cone calorimeter produced much lower CO yields than would be expected for under-ventilated flaming. . Rigid polyurethanes primarily produced aromatic compounds in the condensed phase products of decomposition, whereas flexible polyurethanes produced aromatics, alcohols, aldehydes and heterocycles. CO yields are generally very low for well-ventilated conditions (in the absence of halogens) but increase considerably under-ventilated combustion conditions. 1 The effect of asphyxiants and deep lung irritants depend on the accumulated doses, i.e. Voorhees suggested that the compound was a bicyclic phosphate compound and noted grand mal seizures followed by death in rats with a loading as low as 4% by weight of the fire retardant. However, as noted by Paabo and Levin (1987), many studies into the decomposition of polyurethane foams do not differentiate between flaming and non-flaming decomposition, and focus on the temperature of decomposition rather than the presence of flames. HCN analysis was performed using infrared (IR) spectroscopy using a short path-length gas cell, which is a questionable method for the quantification of HCN due to its poor IR absorption, high potential for interferences and a poor limit of detection. Non-fatal UK fire injuries requiring hospital treatment, 1955-2013 (UK Fire Statistics 2013). The reported yields for the tests performed can be found in Table8. (1981) on polycarbodiimides and polyureas enabled the determination of the source of the organonitriles and HCN during thermal decomposition. When a liquid fuel gives off enough vapors so that it can be . Garrido and Font (2015) reported two main steps in the inert-atmosphere decomposition of flexible polyurethane foams. The relation of the FED to the material-LC50 is given in equation4. Its widespread availability has encouraged its adaptation to toxic gas generation and assessment. 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. In some bench-scale apparatus the heat flux is constant, and often insufficient to sustain flaming at such low oxygen concentrations; further, an unknown quantity of fresh air bypasses the fire plume, so the ventilation condition, and hence, remains undefined. These types of approaches have used existing rat lethality data, as described in ISO 13344 (1996) or more recently, based on the best available estimates of human toxicity thresholds as described in ISO 13571 (2007). For example, polyurethane foam, when burned, gives off cyanide gas. combustion modified high resilience polyurethane foam, Alarie Y (2002) Toxicity of Fire Smoke. Both authors read and approved the manuscript. At high concentrations these acids can cause pulmonary oedema and death (Paul et al. Experimental data reported a 28% recovery of DAT which supports the proposed decomposition mechanism. In particular, the ventilation condition has a critical effect on the yield of the two major asphyxiants, carbon monoxide and hydrogen cyanide. (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. In another investigation, using a steady state tube furnace, Blomqvist et al. As polyols are prepolymers, their molecular mass is relevant to their application, with flexible foams being derived from 1000 to 6000 daltons and few hydroxyl groups, while those used in rigid foams have short chains from 250 to 1000 daltons with high functionality (312 hydroxyl groups per chain). 2012). (2011) Aerospace series - Burning behaviour of non-metallic materials under the influence of radiating heat and flames - Determination of gas components in the smoke; ABD 0031 Fire-Smoke-Toxicity (FST) Test Specification (Airbus Industries); Boeing BSS 7239, Test method for toxic gas generation by materials on combustion. The test method that produced toxic product yields associated with under-ventilated flaming was the NBS cup furnace toxicity method, which yielded 180210mgg1 of CO and 1620mgg1. Thermal decomposition of polyurethanes is usually the reverse of polymerisation, resulting in the formation their precursor functional compoundsdiisocyanates, diamines and dihydroxy compounds. 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. By using this website, you agree to our The steady state tube furnace (ISO/TS 19700 2013), shown in Fig. In most countries, there are no regulations covering the fire toxicity of building components, or for most road vehicles, including goods vehicles in tunnels. Under well-ventilated flaming (<0.8), the yields of CO2 and NO2 were at their highest, while the yields of CO and HCN were at their lowest. When a liquid fuel gives off enough vapors so that it can be ignited and burn, has reached its? Thermal Decomposition of Polyether-based, Water-blown Commerical type of Flexible Polyurethane Foam. 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. Known as "solid gasoline" in the insurance industry, once a polyurethane fire starts, it usually results in a total loss of property and loss of life, according to Federated Insurance. (1972). The authors tested a rigid polyurethane foam using a NBS cup furnace (as described in Levin et al. 3) (Aneja 2002). Does the foam give off toxic fumes if burned? 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. Almost all unwanted fires are diffusion flames, with inefficient mixing of fuel and oxygen(as opposed to the "premixed" flames found in burner/combustion systems). This results in relativelyhigh yields of CO and HCN during under-ventilated flaming and relatively low yields during well-ventilated flaming. Unlike carbon monoxide which remains primarily in the blood (as COHb), the cyanide ion is distributed throughout the extra-cellular fluid of tissues and organs (ISO 13571 2007). Equations2 and 3 have been taken from ISO 13571 (2007). It can continue to irritate people sensitive to chemicals or odors . In this modification, the controlled atmosphere cone calorimeter (CACC) (Babrauskas et al. However, no amines were detected in the vapour phase. 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. The revised protocol is based on continuous sampling of the fire effluent. A detailed understanding of the thermal decomposition chemistry of polyurethane foams is necessary in order to relate the toxicants generated during bothflamingand non-flaming combustion of the polymer to its structure. It gives off toxic gasses and smoke, which makes it difficult to evacuate and put out a fire. The average CO yield expected from under-ventilated flaming is ~200mgg1 for polyurethane materials. 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. However, in the field of combustion toxicity testing, this under-ventilated burning is the most difficult to create using bench-scale apparatus. An understanding of the relative reaction rates is vital in controlling the production of the polymer and producing the desired physical properties (Herrington & Hock 1998). Energy and Buildings 43:p498506, Stec AA, Hull TR (2014) Fire Toxicity Assessment: Comparison of Asphyxiant Yields from Laboratory and Large Scale Flaming Fires. In others, under reduced oxygen concentrations, the fuel lifts from the surface, but ignition does not occur (Christy et al. One analysis of fire victims' blood showed a trend of declining COHb and a rise in cyanide concentrations (Anderson et al. al, 2014). The half-scale ISO 9705 experiments showed a wider range of ventilation conditions up to ~2.0. But the amount & rate of release are affected . During these tests, the PIR was set up as wall panels covered on two faces with aluminium foil. Alongside the experiments performed in the steady state tube furnace, the PIR was also investigated in a half scale ISO 9705 room-corridor test and in a full size ISO 9705 (1993) room. The carbon dioxide release by the reaction in Scheme2 can act as a blowing agent in polyurethane foam production and up to a point the amount of water added will be inversely proportional to the density of the foam. The authors studied decomposition at 900C of foams, partly decomposed foams, smokes, and pure MDI to assess the hydrogen cyanide (HCN) content and noted that the yields of HCN were directly related to the nitrogen content. The authors presented a large set of data for all of the test methods, including a range of test conditions, air flow rates, oxygen concentration, and mass loadings. The data was presented as material-LC50 values for 30min exposures with 14-day post-exposure of test animals and can be found in Tables10, 11 and 12. While there were some problems, the data does show that the yields of toxicants from the polyurethane foam were generally most representative of post-flashover conditions in the test methods that were designed for ventilation controlled conditions, such as the steady state tube furnace and the controlled atmosphere cone calorimeter. Equation 2 calculates the FED of the major asphyxiants, CO and HCN, but without taking oxygen depletion or CO2 driven hyperventilation into account. Does Polyurethane Foam Give Off Toxic Fumes? 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. 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). Taking this into consideration, the reported yields of isocyanates, aminoisocyanates and amines are still relevant, as the results of Blomqvist et al. HCN, in particular, contributes significantly to the overall fire toxicity of polyurethane foams. The three compartments were connected by doors and the target room contained an open vent. Isocyanates were primarily produced during the first stage, and in the second stage primarily carbonyls (R2-C=O) and hydrocarbons were detected using infrared analysis. ISBN 978-953-51-0726-2, Gottuk DT, Lattimer BY (2002) SFPE Handbook of Fire Protection Engineering, 3rd ed. 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. When a one gram sample of foam was decomposed in air, CO was formed at a lower temperature than in nitrogen (300C vs 400C), with a relative concentration of 5000ppm at 500C. 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. 9). When the black char was burned at 600C, it yielded 14.95mg of HCN (65mg per gram of char) and the yellow oil yielded 21mg per gram of oil. (1991b) wherein polyurethane containing a phosphate fire retardant caused immediate death of all of the animals. The severity of the effects increases with dose (Hartzell 1993). In China and Japan, there are specific restrictions on the use of materials with high fire toxicity in high risk applications such as tall buildings, while an increasing number of jurisdictions permit the alternative performance based design approaches to fire safety. As the main reactive group that isocyanates react with, polyols are a major component of the resulting polyurethane product. At high concentrations nitric oxide is rapidly oxidised in air to form nitrogen dioxide, however, at the concentrations found in fire gases, most of the nitric oxide remains unoxidised. Fire Safety Journal 43:243251, Piiril PL, Meuronen A, Majuri ML, Luukkonen R, Mntyl T, Wolff HJ (2008) Inflammation and functional outcome in diisocyanate-induced asthma after cessation of exposure. Again, above 600C the compound and any yellow smoke present was decomposed into smaller volatile fragments. The authors tested a rigid polyurethane foam using a NBS cup furnace (as described in Levin et al. This steric hindrance can be offset by increasing the temperature of the reaction or by performing the reaction in the presence of a catalyst (Vilar 2002). Around 1015% of the nitrogen in the polymer can be converted into HCN with some being released in isocyanates, aminoisocyanates and amines in the fire effluent. McKenna, S.T., Hull, T.R. 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). These yields are comparable to that of the results reported by Blomqvist et al. 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). At 1000C the hydrogen cyanide produced accounted for a range of between 3.8 and 7.3% by weight. NBSIR 832719. Most bench-scale methods have non-constant combustion conditions, such as those in closed chambers exposed to a constant source of heat, including the smoke density chamber (SDC) (ISO 56592 2012), and static tube furnace tests, such as the NF X 70100 (2006). PubMedGoogle Scholar. Memory foam is a type of polyurethane foam. However, when >2.0 the yield of HCN decreased, falling to 10mgg1 at ~2.75. The dimerisation of two isocyanates is a reversible reaction that produces uretidione ring (Scheme6). The reaction of a urethane with another isocyanate will produce an allophanate (Scheme 5). (2007). However, the presence of Cu2O reduced the HCN generated by the flexible polyurethane foam by 70-90% at low temperatures. Carbodiimides are produced by the reaction of isocyanates in the presence of a catalyst (such as phospholine oxides) (Scheme8) (Avar et al. City, Salt Lake, UK Fire Statistics 2013 (and preceding years) United Kingdom, Fire Test Procedure Code (2010) Maritime Safety Committee, (MSC 87/26/Add.3) Annex 34, Part 2 Smoke and Toxicity Test. Further decomposition occurred about 600C with the fragmentation of the yellow smoke, primarily into hydrogen cyanide and small quantities of acetonitrile, acrylonitrile and benzonitrile. As polyurethane foams have very low thermal inertia, application of heat or a small flame can be enough to ignite them. Damage was most severe to the exterior. eff, should be used, rather than an averaged local equivalence ratio, based on the oxygen supply to the chamber, because, in some experiments, substantial secondary flaming occurred outside the test chamber, such that the amount of oxygen available to combustion exceeded the amount that was fed to the enclosed chamber. For a fixed chamber volume (0.51m3), assuming complete combustion, the sample thickness will dictate the ventilation condition, thus a thin sample will burn under well-ventilated conditions with minimum toxic products, while a thicker sample might be expected to produce a high yield of CO and other products of incomplete combustion. Additionally, the authors suggested the positions on the polyol chain where bond scission could occur, explaining the presence of the short-chain alkenes, aldehydes and ketones (Scheme9). P.J. 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, this did not take into consideration the incapacitating effects of the release of irritant gases. 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. Download resource In a real fire, involving cycles of growth and decay of flaming combustion, the resulting yields of HCN from the combustion of polyurethane foams are likely to be higher than predicted in some bench-scale methods as a result of this two-step decomposition mechanism. When =1 the theoretical amount of air is available for complete combustion to carbon dioxide (CO2) and water. VOCs have the ability to vaporize, or off-gas, at room temperature. National Bureau of Standards, Washington D.C. Babrauskas V, Harris RH, Braun E, Levin BC, Paabo M, Gann RG (1991a) The role of bench-scale test data in assessing real-scale fire toxicity, Technical Note 1284, National Bureau of Standards and. Diesel engines use the principle of _____ to ignite fuel vapor.
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