Work by Guo et al. 1982) to that of a large scale test room. 24-Hr. 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. So my dog ate some of the “great stuff” foam insulating foam filler. ISO/TS 19700 (2013) Controlled equivalence ratio method for the determination of hazardous components of fire effluents – the steady state tube furnace. 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. Prog Energy Combust Sci 21:197–237, Purser DA (2002) Toxicity Assessment of Combustion Products, The SPFE Handbook of Fire Protection Engineering 3rd Edition, Edited by DiNenno, P.J. The two main families of polyols used are polyether polyols and polyester polyols (Fig. Unlike urea formaldehyde, polyurethane foam is fully cured before construction. Using the methodology in ISO 13344, the authors also calculated the fractional effective dose (FED) of the individual toxicants sampled. Ann occup Hyg 19:269–273, Levchik SV, Weil ED (2004) Thermal Decomposition, combustion and fire-retardancy of polyurethanes - a review of the recent literature. Again, above 600 °C the compound and any “yellow smoke” present was decomposed into smaller volatile fragments. (2015) questioned their methodology and noted that the authors did not address the release of HCl and its contribution to the acute fire toxicity of the fire retarded foam. However, the lower yields can be attributed to the fact that the cone calorimeter is a well-ventilated scenario, estimated as ϕ ~0.7 (Schartel & Hull 2007). And if that alone isn’t bad enough they are carcinogenic to humans. The authors made this assertion based on the yield of average CO from post-flashover fires being 200 ± 9 mg g−1. Appropriate formulation affords a degree of control over the cross-linking in the polymer without the need for additional cross-linking agents. 2012). 11) ultimately giving well-ventilated flaming. The full size ISO 9705 test resulted in well-ventilated flaming (ϕ 0.26–0.5) due to the relatively large volume of air and relatively small sample size. Polymer International 53:p1585–1610. When ϕ = 1 the theoretical amount of air is available for complete combustion to carbon dioxide (CO2) and water. An FED equal to one indicates that the sum of concentrations of individual species will be lethal to 50 % of the population over a 30 min exposure. However, when this type of foam contained a reactive phosphate fire retardant, the combustion products caused grand mal seizures and death in rats. The results of these experiments and the mechanism of decomposition derived correlated well with work by Rein et al. 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). 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). Over 90 % of all industrial polyurethanes are based on either TDI or MDI (Avar et al. 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. The polyester fabric produced 92–93 mg g−1 of CO when burned with very little difference in the flaming or non-flaming conditions. 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 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. It is not intended to be a critical evaluation of the various test methods or procedures used or the data obtained using these methodologies. 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). This amine may then undergo further reaction with other isocyanates present to produce a urea (Scheme 3). A large majority of the literature indicates that the addition of fire retardants does not increase toxicity of polyurethane foams. 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). A "combustion modified high resilience" flexible polyurethane foam (CMHR-PUF) and a polyisocyanurate (PIR) foam were analysed a steady state tube furnace apparatus. (2003) used a cone calorimeter to assess the yields of amines, aminoisocyanates and isocyanates from the flaming combustion of a flexible polyurethane foam. A summary of the bond decomposition temperatures in polyurethanes is shown in Table 2 (Gharehbagh & Ahmadi 2012). In the UK, the rapid rise in fire deaths, in particular those from smoke toxicity, between the late 1950s and the early 1980s has been attributed to the rapid growth in low cost polyurethane foam furniture, with superior comfort and lower cost than the natural fillings that preceded it. The smoke density chamber (ISO 5659-2) showing a sampling probe for fire smoke toxicity. MDI and TDI both need to be handled carefully during the manufacturing process. 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. 3) (Aneja 2002). Fire Safety Journal 43:243–251, Piirilä PL, Meuronen A, Majuri ML, Luukkonen R, Mäntylä T, Wolff HJ (2008) Inflammation and functional outcome in diisocyanate-induced asthma after cessation of exposure. 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. Once sensitisation has occurred, even extremely low concentrations of airborne isocyanates can trigger fatal asthma attacks (Henneken et al. The flexible foam produced ~175 mg g−1 of CO and 5 mg g−1 of HCN. In an attempt to improve the understanding of the thermal decomposition of polyurethanes, Rogaume et al. 2 It's likely that the MDI food grade polyurethane is a lot less toxic than the TDI polyurethane foam. Other materials are added to aid processing the polymer or to modify the properties of the polymer. Diisocyanates react with polyols to produce the flexible memory foam. ϕ depends on the mass loss rate of the specimen and the available air; for most methods one or both are unknown; ϕ will be increased by an unknown factor if products are recirculated into the flame zone. The data was presented as material-LC50 values for 30 min exposures with 14-day post-exposure of test animals and can be found in Tables 10, 11 and 12. Equation 3 uses a similar principle to equation 1 to estimate the combined effect of all irritant gases. 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. 1999). Apparatus where ϕ changes rapidly allow little time for sampling and measurement of mass loss and effluent composition at a specific value of ϕ, with resultant errors and uncertainties. The presence of oxygen in the atmosphere directly interacts with the solid phase, which accelerates decomposition. Fire Safety Science 11:p404–418, Stec AA, Hull TR, Lebek K (2008) Characterisation of the steady state tube furnace (ISO TS 19700) for fire toxicity assessment. Fire Safety Journal 40:439–465, Aneja A (2002) Chapter 2, Structure–property Relationships of Flexible Polyurethane Foams, PhD. Additionally, the self-addition of isocyanates to produce isocyanurates (v in Fig. 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). To learn more about our Durethane® F foam technologies, click here. Non-fatal UK fire injuries requiring hospital treatment, 1955-2013 (UK Fire Statistics 2013). Polyols are binding compounds that are essential to creating the polyurethane foam. In the smoke chamber, the highest reported yield during flaming combustion was 1.02 mg g−1. 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). 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. 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). The authors proposed that once formed, these compounds could partially polymerise with volatilised TDI in the vapour phase to produce Woolley’s “yellow smoke”. Substituted ureas decompose between 235 and 250 °C and carbodiimides decompose between 250 and 280 °C. 1). 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 83–2678, 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. National Fire Protection Association, 82, p 161, Vilar WD (2002) Chemistry and Technology of Polyurethanes - Chapter 1. In terms of hazard, carbon monoxide (CO) is typically the most abundant toxicant in fires under almost all combustion conditions. However, unlike a real fire, the heat flux remains constant, and so when the oxygen concentration falls, the flame may be extinguished. 2008; Kaplan 1987b). Andersson B, Markert F, Holmstedt G (2005) Combustion products generated by hetero-organic fuels on four different fire test scales. 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. 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. Part of 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 (3–12 hydroxyl groups per chain). 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. 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. (2007) assessed the toxic product yields of a flexible polyurethane foam that was designed for use in hospital mattresses. 1981), probably because of increased use of nitrogen-containing synthetic polymers. The authors declare that they have no competing interests. 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. Purser model, [AGI] is the concentration of inorganic acid gas irritants, [OI] is the concentration of organic irritants, A is an acidosis factor equal to [CO2] × 0.05. Polyether polyols are more resistant to hydrolysis, but less stable to oxidation, while for polyester polyols it is the opposite. 9). Hexamethylene diisocyanate (HDI) (i), 1,5-naphthalene diisocyanate (NDI) (ii) and isophorone diisocyanate (IPDI) (iii). LC50 values should be referenced to the fire condition under which they were measured. Some fire models, such as the cone calorimeter, fire propagation apparatus and smoke density chamber use the temperature of the radiant heater to preselect the radiant heat flux, and then check this using a radiant heat flux meter. Reliable rate of heat release, fire effluent toxicity and smoke generation data are all essential components of such an assessment. The polyisocyanurate, on the other hand, produced slightly more HCN than the rigid foam (17 mg g−1 vs 12 mg g−1). 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. Fire Res 1:p11–21. Work by Ravey and Pearce (1997) on the decomposition of a polyether based flexible polyurethane foam suggested that up to 360 °C the decomposition of the foam was achieved by two main mechanisms. A detailed understanding of the thermal decomposition chemistry of polyurethane foams is necessary in order to relate the toxicants generated during both flaming and non-flaming combustion of the polymer to its structure. The cone calorimeter (ISO 5660–1 2002) is probably the most widely used apparatus for measurement of flammability properties such as ignitability and heat release rate (Schartel & Hull 2007). 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. Carbodiimides are produced by the reaction of isocyanates in the presence of a catalyst (such as phospholine oxides) (Scheme 8) (Avar et al. 4). The use of 13C labelling by Chambers et al. 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. Isocyanates are a highly reactive family of compounds that are characterised by the R − N = C = O functional group (where R can be any aliphatic or aromatic functionality). The radiant heat apparatus, smoke chamber and controlled atmosphere cone calorimeter produced much lower CO yields than would be expected for under-ventilated flaming. The sample is spread evenly in a silica boat over a length of 800 mm and fed into a tube furnace at a typical rate of 1 g min-1 with flowing air at a rate of 2-10 L min-1. Draeger tubes), conventional or Fourier transform infrared spectroscopy (FTIR) gas analysis, despite significant problems of reproducibility. Today, polyurethane foams can be found in cars, mattresses, baby products and just about everywhere. 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. Both authors read and approved the manuscript. $$ \begin{array}{l}\mathrm{FED}=\left\{\frac{\left[\mathrm{C}\mathrm{O}\right]}{{\mathrm{LC}}_{50,\;\mathrm{C}\mathrm{O}}}+\frac{\left[\mathrm{H}\mathrm{C}\mathrm{N}\right]}{{\mathrm{LC}}_{50,\;\mathrm{H}\mathrm{C}\mathrm{N}}}+\frac{\left[\mathrm{A}\mathrm{G}\mathrm{I}\right]}{{\mathrm{LC}}_{50,\;\mathrm{A}\mathrm{G}\mathrm{I}}}+\frac{\left[\mathrm{O}\mathrm{I}\right]}{{\mathrm{LC}}_{50,\;\mathrm{O}\mathrm{I}}}\dots \right\}\times {\mathrm{V}}_{{\mathrm{CO}}_2}+\mathrm{A}+\frac{21-\left[{\mathrm{O}}_2\right]}{21-5.4}\\ {}{\mathrm{V}}_{{\mathrm{CO}}_2}=1\kern0.36em +\kern0.36em \frac{ \exp \left(0.14\left[{\mathrm{CO}}_2\right]\right)-1}{2}\end{array} $$, $$ \mathrm{FED}={\displaystyle \sum_{t_1}^{t_2}\frac{\left[\mathrm{C}\mathrm{O}\right]}{35\;000}}\;\Delta t+{\displaystyle \sum_{t_1}^{t_2}\frac{ \exp \left(\left[\mathrm{H}\mathrm{C}\mathrm{N}\right]/43\right)}{220}}\;\Delta t $$, $$ \mathrm{F}\mathrm{E}\mathrm{C}=\frac{\left[\mathrm{H}\mathrm{C}\mathrm{l}\right]}{{\mathrm{IC}}_{50,\;\mathrm{H}\mathrm{C}\mathrm{l}}}+\frac{\left[\mathrm{H}\mathrm{B}\mathrm{r}\right]}{{\mathrm{IC}}_{50,\;\mathrm{H}\mathrm{B}\mathrm{r}}}+\frac{\left[\mathrm{H}\mathrm{F}\right]}{{\mathrm{IC}}_{50,\;\mathrm{H}\mathrm{F}}}+\frac{\left[{\mathrm{SO}}_2\right]}{{\mathrm{IC}}_{50,\;{\mathrm{SO}}_2}}+\frac{\left[{\mathrm{NO}}_2\right]}{{\mathrm{IC}}_{50,\;{\mathrm{NO}}_2}}+\frac{\left[\mathrm{acrolein}\right]}{{\mathrm{IC}}_{50,\;\mathrm{acrolein}}}+\frac{\left[\mathrm{fomaldehyde}\right]}{{\mathrm{IC}}_{50,\;\mathrm{fomaldehyde}}}+{\displaystyle \sum \frac{\left[\mathrm{irritant}\right]}{{\mathrm{IC}}_{50,\;\mathrm{irritant}}}} $$, $$ \mathrm{material}\hbox{-} {\mathrm{LC}}_{50}=\kern0.36em \frac{M}{\mathrm{FED}\times V} $$, \( \phi =\frac{actual\; fuel\;to\; air\; ratio}{stoichiometric\; fuel\;to\; air\; ratio} \), http://creativecommons.org/licenses/by/4.0/, https://doi.org/10.1186/s40038-016-0012-3. The PIR at ϕ 1.75 resulted in 15 % of the fuel nitrogen being recovered as HCN. Global usage is expected to expand from 13.65 Mt in 2010 to 17.95 Mt by 2016. Fire retardants, such as gas-phase free radical quenchers, have been reported to increase the yields of CO in well-ventilated conditions by preventing the oxidation of CO to CO2. In their raw forms, these can cause respiratory and skin damage. The resulting substituted urea can then react with another isocyanate to produce a biuret linkage (Scheme 4). Toxicity occurs only during manufacture and curing. The results showed a HCN yield of 15.8 mg g−1 at 600 °C. The relation of the FED to the material-LC50 is given in equation 4. When a one gram sample of foam was decomposed in air, CO was formed at a lower temperature than in nitrogen (300 °C vs 400 °C), with a relative concentration of 5000 ppm at 500 °C. This versatile material can be transformed from a solid to a foam by introducing blowing agents that generate tiny air bubbles in the material matrix. 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). 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. (1981) on polycarbodiimides and polyureas enabled the determination of the source of the organonitriles and HCN during thermal decomposition. 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. 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. This makes the isocyanate functional group highly reactive towards nucleophiles with an available hydrogen. 1992), shown in Fig. Toxicity of polyurethane foams is restricted to the manufacturing process, except during fires. Babrauskas et al. Toxicology 47:165–170, Kaplan HL, Grand AF, Hartzell GE (1984a) Toxicity and the smoke problem. 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. Equation 2 represents the generally accepted case that there are only two significant asphyxiant fire gases, CO and HCN. Analysis of the compound, trimethylol propane phosphate (TMPP), by Kimmerle (1976) found it to have a high acute toxicity when tested on rats. Rigid MDI based foams are primarily used for insulation in the construction industry and can also be found in the transport industry. In general conversion efficiencies are high for halogen acid gases. 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. Polyurethane is widely used, with its two major applications, soft furnishings and insulation, having low thermal inertia, and hence enhanced flammability. Fire and Materials 9:p125–134, Levin BC, Paabo M, Bailey CS, Harris SE (1986) Toxicity of the combustion products from a flexible polyurethane foam and a polyester fabric evaluated separately and together by the NBS Toxicity Test Method. 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. 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 open cone calorimeter replicates the early well-ventilated stage of flaming where a fire would be too small to produce enough toxicants to cause harm except in very small enclosures. Preliminary calculations suggested that 27 % of the TDI should be recovered as DAT. Synthetic polymeric materials may be divided into thermoplastics and thermosets. The polyurethanes used were elastomers based on TDI, which could potentially have differing decomposition mechanisms to their foam counterparts. Many foams use greenhouse gases as blowing agents, and thus must comply with legal guidelines mandating thickness levels and distribution arrays. LAST-A-FOAM ® rigid CFC-free polyurethane foam boards and products are cost-effective, versatile, strong and durable. The polyester based polyurethane began to decompose at 284 °C with a secondary decomposition step at 359 °C. Is Thermoset Polyurethane Foam Toxic? ISO 13571 (2007) considers the four major hazards from fire which may prevent escape (toxic gases, irritant gases, heat and smoke obscuration). The most commonly reported adverse health effects after airborne isocyanate exposure is asthma due to sensitisation (Piirilä et al. With an increasing concern around toxins in plastics, product designers often question if thermoset polyurethane foam is considered a safe material for consumer and environmental use. 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. Data from large scale fires in enclosures, such as a room, shows much higher levels of the two of the major toxicants, carbon monoxide (CO) and hydrogen cyanide (HCN) under conditions of developed flaming (Andersson et al. Flaming combustion of the polyurethane foam did not cause any animal deaths, however the non-flaming combustion resulted in deaths post-exposure. McKenna, S.T., Hull, T.R. Journal of Analytical and Applied pyrolysis 108:p143–150, Hartzell G (1993) Overview of Combustion Toxicology. Further fragmentation of these molecules led to the production of HCN, acetonitrile, acrylonitrile and a range of olefinic fragments. A summary of these structures is shown in Fig. Chem Co., Dow, Hertzberg T, Blomqvist P, Dalene M, Skarping G (2003) Particles and Isocyanates from Fires. What is Polyurethane Foam? Polyol fragments in the gas phase will also begin to decompose at >800 °C to produce simple organic fragments and PAHs. This is due to the concentration of oxygen directly under a flame being close or equal to 0 % (Schartel & Hull 2007). Fragmentation of these structures is shown in Table 2 ( Gharehbagh & Ahmadi 2012 ) ) the. And the mechanism of decomposition derived correlated well with work by Rein et al blowing,! Condition under which they were measured a urea ( Scheme 3 ) Hartzell G ( 2005 ) combustion products by. Combustion of the organonitriles and HCN during thermal decomposition Durethane® F foam technologies, click here everywhere... Conventional or Fourier transform infrared spectroscopy ( FTIR ) gas analysis, despite problems... 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