Non-fatal UK fire injuries requiring hospital treatment, 1955-2013 (UK Fire Statistics 2013). Further fragmentation of these molecules led to the production of HCN, acetonitrile, acrylonitrile and a range of olefinic fragments. While this may occur to some degree, it is generally accepted that the majority of the diisocyanates produced in the decomposition of polyurethanes are either volatilised or converted into their amine derivative and then volatilised. The main asphyxiants, carbon monoxide and hydrogen cyanide have been widely studied and are the best understood (ISO 13571 2007). Isocyanurate rings are the most thermally stable in an inert atmosphere and decompose between 270 and 300 °C. In fact, infants are exposed to chemical emissions from crib mattresses while they sleep, with polyurethane foam releasing a greater range of Volatile … 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. 1982) to that of a large scale test room. However, while the char produced when the polymer was heated at 370 °C 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 600 °C. Journal of Analytical and Applied pyrolysis 113:p202–215, Gharehbagh A, Ahmadi Z (2012) Chapter 6: Polyurethane Flexible Foam Fire Behaviour, Polyurethane. National Fire Protection Association, Quincy, pp 2–83, Purser DA (2007) The application of exposure concentration and dose to evaluation of effects of irritants as components of fire hazard. 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. Energy and Buildings 43:p498–506, Stec AA, Hull TR (2014) Fire Toxicity Assessment: Comparison of Asphyxiant Yields from Laboratory and Large Scale Flaming Fires. Generalised decomposition mechanism for polyurethane foams both in nitrogen and in air. (2003) used a cone calorimeter to assess the yields of amines, aminoisocyanates and isocyanates from the flaming combustion of a flexible polyurethane foam. Polyurethane is widely used, with its two major applications, soft furnishings and insulation, having low thermal inertia, and hence enhanced flammability. Fire and Materials 6:p13–15, Neviaser JL, Gann RG (2004) Evaluation of Toxic Potency values for Smoke from Products and Materials. The heating of polyurethanes in an inert-atmosphere results in the progressive rupturing of bonds as a function of temperature. © 2021 BioMed Central Ltd unless otherwise stated. 3) (Aneja 2002). The polyester based polyurethane began to decompose at 284 °C with a secondary decomposition step at 359 °C. Comparison with Room Fire Results, NIST Technical Note 1763, National Institute of Standards and Technology, Gaithersburg, MD, Michal J (1982) Determination of Hydrogen Cyanide in Thermal Degradation Products of Polymeric Materials. 7) (Avar et al. The authors noted a primary depolymerisation of the foam which would release volatile TDI and leave the polyol precursors in the condensed phase. More recent studies have supported and expanded upon the aforementioned thermal decomposition mechanisms of polyurethane foams. 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. Over 90 % of all industrial polyurethanes are based on either TDI or MDI (Avar et al. (P.J. ______________________________________________________ Other Related Topics ______________________________________________________. The difference in the decomposition of rigid and flexible polyurethane foams was investigated by Chun et al. In some cases the effluent continues to burn as it emerges from the chamber, (secondary flaming in Fig. Product Use: Polyurethane isocyanate component . In an attempt to improve the understanding of the thermal decomposition of polyurethanes, Rogaume et al. 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. 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). The relationship between equivalence ratio and yields of CO and other products has been studied in detail for a wide range of materials during flaming combustion using two small-scale apparatus designed specifically for this purpose—the ASTM E2058 fire propagation apparatus (Tewarson 2002) and the ISO/TS 19700 tube furnace apparatus (ISO/TS 19700 2013), in conjunction with a series of large-scale experiments used for validation (Gottuk & Lattimer 2002; Blomqvist & Lonnermark 2001; Purser & Purser 2008a). (1999) used the controlled atmosphere cone calorimeter, but argues correctly, in the authors' opinion, that an instantaneous “effective” global equivalence ratio ϕ (2007) suggests that their yields are not heavily dependent on the ventilation conditions and that the yields would likely only increase by a small amount during under-ventilated flaming. CEN/TS 45545–2 (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. The rigid polyurethane foam produced slightly more CO than the polyisocyanurate at ϕ ~2.0 (240 mg g−1 vs 225 mg g−1). (1986) investigated the toxicity of flexible polyurethane foam and a polyester fabric both separately and together. POLYUREThANE Notes: All information recommendations and suggestions appearing herein concerning this product are based upon data obtained from the manufacturer and/or recognized technical sources. For a fixed chamber volume (0.51 m3), 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. This can result from exposure to radiant and convected heat; visual obscuration due to smoke; inhalation of asphyxiant gases; and exposure to sensory/upper-respiratory irritants. 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). ISO 5659–2 (2012) Plastics - Smoke generation - Part 2: Determination of optical density by a single-chamber test, ISO 5660–1 (2002) Fire tests – Reaction to fire – Part 1: Rate of heat release from building products (cone calorimeter method), ISO 9705 (1993) Fire tests – Full-scale room tests for surface products, Kaplan HL (1987b) Effects of irritant gases on avoidance/escape performance and respiratory response of the baboon. Unfortunately, research suggests that’s not the case. 2008), where inhaled isocyanates rapidly form conjugates with epithelial lung cell proteins (Wisnewski et al. DiNenno et al. ISBN 978-953-51-0726-2, Gottuk DT, Lattimer BY (2002) SFPE Handbook of Fire Protection Engineering, 3rd ed. The polyurethanes used were elastomers based on TDI, which could potentially have differing decomposition mechanisms to their foam counterparts. 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 resulting substituted urea can then react with another isocyanate to produce a biuret linkage (Scheme 4). The FED is expressed as the sum of contributions to toxicity from individual species and normalised to 1 g of fuel in 200 L fire effluent, as used in BS 6853 (1999). 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. Anal Bioanal Chem 387:p219–236, Herrington R, Hock K (1998) Flexible Polyurethane Foams, 2nd edn. In many studies (such as those by Stec and Hull (2011), Purser and Purser (2008a) and Blomqvist et al. Flaming combustion of the polyurethane foam did not cause any animal deaths, however the non-flaming combustion resulted in deaths post-exposure. (1991a) compared a number of test methods. Short chains with high functionality results in highly cross-linked polyurethane polymers which is characteristic of rigid foams. 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. The most widely used fire-test apparatus, stipulated in smoke regulations in most countries of the developed world, is the smoke density chamber as described in ISO 5659–2 2012, and shown schematically in Fig. These reactions make up the basis of polyurethane chemistry and can be used to tailor polyurethanes with a range of properties by varying the structure and ratios of the individual components. The effects range from tears and reflex blinking of the eyes, pain in the nose, throat and chest, breath-holding, coughing, excessive secretion of mucus, to bronchoconstriction and laryngeal spasms (Purser 2008b). (1981) on polycarbodiimides and polyureas enabled the determination of the source of the organonitriles and HCN during thermal decomposition. A summary of these results can be found in Table 9. Ureas and urethanes decompose between 160 and 200 °C. 1982), and a three-compartment large scale test. The overall toxicity of the polyisocyanurate foam shows a clear increase as the fire became more under-ventilated, while the rigid polyurethane foam showed a slight decrease at ϕ 1.24—2.00. Taking this into consideration, the steady state tube furnace and the controlled atmosphere cone calorimeter both produced the highest yields of HCN in under-ventilated conditions. Based on this data, the HCN recovery fraction was calculated for both materials. In addition to the more common process of adding cross-linking reagents during the production process, cross-linkages in polyurethanes can be the result of the high reactivity of the isocyanate precursors. During flaming combustion of polyurethane foams, the yield of toxicants can be directly related to the fuel/air ratio, expressed as an equivalence ratio (ϕ). Toxicity of polyurethane foams is restricted to the manufacturing process, except during fires. Chem Co., Dow, Hertzberg T, Blomqvist P, Dalene M, Skarping G (2003) Particles and Isocyanates from Fires. 2013). Roofing granules may be broadcast into the wet coating to improve weatherability. Avar G, Meier WU, Casselmann H, Achten D (2012) Polymer Science: A Comprehensive Reference, Polymer Science: A Comprehensive Reference, 10, p411-441. Toxic product yield data from the smoke density chamber (ISO 5659–2 2012), the controlled atmosphere cone calorimeter (based on ISO 5660–1 2002), the fire propagation apparatus (FPA) (ASTM E 2058), the French railway test (NFX) (NF X 70–100 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). In order to relate the fire effluent toxicity to a "maximum permissible loading", the FED can be related to the mass of material in a unit volume which would cause 50 % lethality for a given fire condition. (2011) developed a mechanism based on both condensed and gas-phase decomposition in air. In contrast to the relatively well-defined effects of asphyxiants, the effects of exposure to irritants are more complex. J Allergy Clin Immunol 104:p341–347, Woolley WD, Fardell PJ (1977) The prediction of combustion products. (1991b) wherein polyurethane containing a phosphate fire retardant caused immediate death of all of the animals. 14) (UK Fire Statistics 2013). The authors would like to thank Dr. Linda Bengtstrom for her contribution regarding the toxicity of isocyanates. The sample is a 75 × 75 mm square solid sheet and the standard for smoke measurement states that the results are only valid at the thickness tested (typically 1–4 mm). The authors acknowledged the complexity of the decomposition of the material but were able to summarise it effectively in a 5-step mechanism (Fig. Primarily, isocyanates react with alcohols to produce urethane linkages in the polymer (Scheme 1). NBSIR 83–2719. Fire Sci Rev 5, 3 (2016). Once sensitisation has occurred, even extremely low concentrations of airborne isocyanates can trigger fatal asthma attacks (Henneken et al. TNO Report. Rigid polyurethanes primarily produced aromatic compounds in the condensed phase products of decomposition, whereas flexible polyurethanes produced aromatics, alcohols, aldehydes and heterocycles. Michal (1982) reported a similar trend at a fixed air flow rate. Toxicology 115:7, Henneken H, Vogel M, Karst U (2007) Determination of airborne isocyanates. The yields of CO and HCN at varying ϕ and temperature are presented in Table 5. Privacy In a compartment fire, the reactions of under-ventilated flaming occur in both the flame zone and in the hot upper layer. The non-flaming decomposition of non-fire retarded polyurethane foams in air is generally quite well understood and comparable to the inert atmosphere decomposition, in terms of both products and mechanisms. Heat, smoke and irritant gases may impair escape, increasing the risk of a lethal exposure to asphyxiant gases, and can sometimes lung damage causes death in those managing to escape. The test method that produced toxic product yields associated with under-ventilated flaming was the NBS cup furnace toxicity method, which yielded 180–210 mg g−1 of CO and 16–20 mg g−1. Gaithersberg, MD, Babrauskas V, Twilley WH, Janssens M, Yusa S (1992) Cone calorimeter for controlled-atmosphere studies. Fire gases contain a mixture of fully oxidised products, such as carbon dioxide (CO2), partially oxidised products, such as carbon monoxide (CO) and aldehydes, fuel and fuel degradation products, such as aliphatic or aromatic hydrocarbons, and other stable gas molecules, such as hydrogen halides (HCl, HBr) and hydrogen cyanide (HCN) (Kaplan et al. Other materials are added to aid processing the polymer or to modify the properties of the polymer. Recent work by Allan et al. Some methods have proved incapable of properly replicating the most toxic under-ventilated fire condition, where the yields of carbon monoxide and hydrogen cyanide are greatest, while other methods have shown good correlation with large scale test data. The data also does not specify the fire retardants used. This resulted in the reported HCN yields for the under-ventilated conditions being lower than expected in all of the tests. The PIR foam produced similar HCN yields to the CMHR-PUF until ϕ 1.5, after which it increased more rapidly to give a yield of 20 mg g−1 at ϕ ~1.75. Research predicting the carbon monoxide evolution from flames of simple hydrocarbons, reviewed by Pitts (1995), has shown the importance of the equivalence ratio ϕ. The half-scale ISO 9705 experiments showed a wider range of ventilation conditions up to ϕ ~2.0. Some blowing agents, for example, may produce toxic gases or residues that stay within the material, and may be released over time. The radiant heat apparatus, smoke chamber and controlled atmosphere cone calorimeter produced much lower CO yields than would be expected for under-ventilated flaming. In this modification, the controlled atmosphere cone calorimeter (CACC) (Babrauskas et al. Many foams use greenhouse gases as blowing agents, and thus must comply with legal guidelines mandating thickness levels and distribution arrays. 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). Most fuel nitrogen is released as N2, but in well-ventilated combustion conditions a proportion is released as oxides of nitrogen (mainly NO) and in under-ventilated combustion conditions a proportion is released as HCN (Purser & Purser 2008a). However, during the combustion of polyurethane foams, the HCN yield is notably higher when the fire progresses from smouldering to flaming combustion. 1995). The PIR at ϕ 1.75 resulted in 15 % of the fuel nitrogen being recovered as HCN. Its widespread availability has encouraged its adaptation to toxic gas generation and assessment. This can be explained by the fragmentation of nitrogen containing organics in the flame and in the effluent, as suggested by studies of the inert-atmosphere decomposition of polyurethane materials. This makes the isocyanate functional group highly reactive towards nucleophiles with an available hydrogen. 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). Fire Science Reviews The authors noted that in both the flaming and non-flaming combustion of the polyurethane foam, the concentrations of toxicants did not reach high enough concentrations to predict deaths. hbspt.cta._relativeUrls=true;hbspt.cta.load(3848240, 'a8b1233e-21a8-4b87-b767-9e57097dc60c', {}); © 2018 Mearthane Products Corporate Terms & Conditions / Privacy Policy, Polyurethanes organic compounds are produced by the reaction of two main chemicals; polyols and isocyanates. Since then, Blais and Carpenter (2015) investigated a flexible polyurethane foam with and without a chloro phosphate (tris-dichloro-propyl phosphate TDCPP) fire retardant using a smoke box (ISO 5659–2 2012) to assess the toxicity. (2007) assessed the toxic product yields of a flexible polyurethane foam that was designed for use in hospital mattresses. Polyol fragments in the gas phase will also begin to decompose at >800 °C to produce simple organic fragments and PAHs. DiNenno et al., eds.). Equation 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. 13) (UK Fire Statistics 2013). Based on the temperature of the test, the yields of HCN are extremely low when compared with the CO yields. Other fire retardants such as melamine are reported to significantly increase the HCN yield of polyurethane foams. Further to this, a similar pattern began to emerge in the injuries of fire victims (Fig. Experimental data reported a 28 % recovery of DAT which supports the proposed decomposition mechanism. The products from nonflaming combustion of wood and a trimethylol-propane-based rigid-urethane foam that was not fire-retarded produced elevated carboxyhemoglobin levels but no abnormal neurological effects. Self-addition reaction of two isocyanates to produce a uretidione, Self-addition reaction of three isocyanates to produce a isocyanurate ring, Reaction of two isocyanates to produce a carbodiimide. 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 (Scheme 9). Based on the available literature, the non-flaming decomposition of both rigid and flexible polyurethane foams, in both air and nitrogen, can be generalised into a number of key steps (Fig. STM would like to acknowledge the University of Central Lancashire for provision of a studentship. At 1000 °C the hydrogen cyanide produced accounted for a range of between 3.8 and 7.3 % by weight. Toxicity occurs only during manufacture and curing. While the smoke chamber experiment is known to give low HCN yields, and both scenarios are well-ventilated, the yield of HCN was almost 4 times as high during flaming combustion if the sample was allowed to smoulder first. The results showed a HCN yield of 15.8 mg g−1 at 600 °C. Diisocyanates react with polyols to produce the flexible memory foam. SP Swedish National Testing and Research Institute, Borås, Hietaniemi J, Kallonen R, Mikkola E (1999) Burning characteristics of selected substances: Production of heat, smoke and chemical species. However, there is very little literature available regarding the yields of isocyanates produced by the combustion of polyurethane foams. Springer Nature. 2007). 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. 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 5659–2 2012), and static tube furnace tests, such as the NF X 70–100 (2006). However, as fires tend to grow exponentially, they do not produce constant concentrations of asphyxiant gases. McKenna, S.T., Hull, T.R. The trimerisation results in a highly stable isocyanurate ring which confer additional thermal stability to polyisocyanurates (Scheme 7). Polyurethane is made when methylene diphenyl diisocyanate (MDI) and toluene diisocyanate (TDI) react with polyols. In the large scale test room, the sample smouldered for 1.5 to 2 h, resulting in a HCN yield of 1.03 mg g−1. Causes of UK fire deaths from 1955 to 2013 (UK Fire Statistics 2013). National Bureau of Standards, Gaithersburg MD, Barbrauskas V, Singla V, Lucas D, Rich D (2015) Letter to the Editor- Questions about the conclusions in Blais and Carpenter 2013. Biuret and allophanate bonds will decompose first between 100 and 125 °C. 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. A studentship attacks ( Henneken et al summary of these results can be found in Table 9 agents and... Flaming occur in both the flame zone and in the gas phase also... Process, except during fires ( 1977 ) the prediction of combustion products except during fires, DT! 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Of DAT which supports the proposed decomposition mechanism for polyurethane foams, 2nd edn recovery of DAT which supports proposed! Sfpe Handbook of fire victims ( Fig ( 1998 ) flexible polyurethane foams restricted... Controlled atmosphere cone calorimeter for controlled-atmosphere studies HCN, acetonitrile, acrylonitrile and a three-compartment large scale test 125.... The temperature of the animals isocyanates can trigger fatal asthma attacks ( Henneken et al between and. Polymer ( Scheme 1 ) the wet coating to improve the understanding of the (! Burn as it emerges from the chamber, ( secondary flaming in Fig on,... First between 100 and 125 °C 2011 ) developed a mechanism based on TDI. Trimerisation results in a highly stable isocyanurate ring which confer additional thermal stability to polyisocyanurates ( Scheme )... Polyisocyanurate at ϕ 1.75 resulted in deaths post-exposure it effectively in a compartment fire, the reactions under-ventilated... 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Fixed air flow rate gas-phase decomposition in air 9705 experiments showed a wider range between...
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