The Model This equation only relates to lethality, or cause of death. The specific mass of the polyurethane sample was not provided by the author and the ventilation conditions were not clear as a result of this. The resulting substituted urea can then react with another isocyanate to produce a biuret linkage (Scheme4). The presence of Cu2O drastically decreased the yield of HCN in polyurethane foams at lower temperatures, but had little effect at high temperatures. The peak HCN value reached was 10mg per g1 in the under-ventilated tests. 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. (1990) also reported increased HCN yields when the sample was allowed to smoulder before flaming in similar apparatus as above. . Technology, Gaithersburg MD, Babrauskas V, Levin BC, Gann R, Paabo M, Harris RH, Peacock RD, Yusa S (1991b) Toxic potency measurement for fire hazard analysis, special publication 827, National Institute of Standards and Technology. Equation2 represents the generally accepted case that there are only two significant asphyxiant fire gases, CO and HCN. Both authors read and approved the manuscript. 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). The difference in the decomposition of rigid and flexible polyurethane foams was investigated by Chun et al. The authors noted that the total concentrations of CO and HCN during flaming combustion were greater than the sum of those from the individual materials. 1982), a developmental method (SwRI/NIST method) which used a radiant heater on the sample which lead into a 200L exposure chamber, a cone calorimeter (ISO 5660 2002), a furniture calorimeter (as described in Babrauskas et al. The isocyanate precursors used in the production of polyurethane foams usually consist of aromatic diisocyanates such as toluene diisocyanate (TDI) and methylene diphenyl diisocyanate (MDI). . Substituted ureas decompose between 235 and 250C and carbodiimides decompose between 250 and 280C. 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 4 At lower temperatures, decomposition differs, depending on the composition and physical properties of the polymer, although clear trends can be identified. The interior of large flames are always under-ventilated, because oxygen cannot penetrate the flame. 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. The CACC and SDC show reasonable agreement for well-ventilated burning, but fail to replicate the more hazardous under-ventilated fire conditions. 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. Hydrogen chloride (HCl) and hydrogen bromide (HBr) are strong acids which dissociate entirely in water. decomposition products will burn. 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. 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). These substances can include carbon dioxide, carbon monoxide, formaldehyde, aldehydes, and other volatile organic compounds (VOCs), as well as soot and particulates. Chambers et al. 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). The authors intended to compare the HCN yields for the non-flaming and flaming combustion of the foam in a smoke chamber apparatus (as described in Levin et al. This will result in a HCN yield related that specific furnace temperature. The guidelines above for choosing a safer mattress or non toxic mattress topper can help determine which . Historically, material-LC50 data has been reported directly based on animal lethality testing, however due to the declining use of animal testing in fire toxicity assessment, calculations based on standard lethality data(such as ISO 13344 1996) are more commonly used. It has been suggested that the reproducibility problems arise from the single point measurement (the tip of the probe may be in the centre of the plume, below it, or if mixing is more efficient, the upper layer may be recirculated through the flame), or the timing of the effluent sampling may cause instabilities (for example an initial proposal to sample after 8min was replaced by a proposal to sample when the smoke density reached its maximum). The polyester fabric produced 9293mgg1 of CO when burned with very little difference in the flaming or non-flaming conditions. The data also does not specify the fire retardants used. Investigator Chapters 1-5 --PART 1--Burns Flashcards | Quizlet TDI is produced as the 2,4- and the 2,6- isomer which have a boiling point of 121C and 120C respectively. 9). 8-80, addressing . 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. 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). 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. 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. Investigations by Hertzberg et al. 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. 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. 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. 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. 5). (1991b) wherein polyurethane containing a phosphate fire retardant caused immediate death of all of the animals. Elemental analysis of the polymer and the char showed that 80% of the nitrogen in the polymer was lost when heated at 370C, but only 0.6% was recovered as HCN when burned at 600C. CO also combines with myoglobin in the muscle cells, impairing diffusion of oxygen to cardiac and skeletal muscles (Purser 2008b). Interflam Conference Proceedings. The applied heat flux must be large enough for burning to continue at oxygen concentrations as low as 5%. Stec and Hull (2011) presented material-LC50 data for rigid polyurethane foam and polyisocyanurate foam, calculated using rat lethality data from ISO 13344 (1996). During polymerisation, isocyanates undergo a number of distinct reactions. Fire and Materials 9:p125134, 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. The fire department was not immediately called, so the oil burned completely. p 1-30. The authors made this assertion based on the yield of average CO from post-flashover fires being 2009mgg1. Does Polyurethane Foam Give Off Toxic Fumes? | Nontoxic Living 11, a conical heater used as a fire model is enclosed in a heat resistant glass chamber (400mm high with 300300mm base) so that the air flowaround the specimen may be controlledby diluting the oxygen content with nitrogen. Spray Foam Insulation FAQs - Foam Kit Solutions Polyurethane Fume Exposure And Your Health: What You Need To Know Ask if the mattress materials are generally free of VOC and HAPs. 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. As with all foams, memory foam compresses under pressure. 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. 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). As the availability of oxygen becomes lower in proportion to the amount of fuel, the yields of certain toxic gases will increase. Fire Safety Science 11:p404418, Stec AA, Hull TR, Lebek K (2008) Characterisation of the steady state tube furnace (ISO TS 19700) for fire toxicity assessment. To a lesser extent, parameters such as temperature and oxygen concentration also affect the yields of toxic products. In particular, the ventilation condition has a critical effect on the yield of the two major asphyxiants, carbon monoxide and hydrogen cyanide. . 1999). From this, the library of data was sorted into categories of combustion/pyrolysis conditions, material/product, type of test animal and toxicological endpoint. 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. At ~2.0 the CMHR-FPUR resulted in 8% and 11% nitrogen recovered as HCN for 650C and 850C respectively. In general, isocyanate (R-NCO) exposure causes irritation to the skin, mucous membranes, eyes and respiratory tract (NIOSH 1989). Flaming combustion of the polyurethane foam did not cause any animal deaths, however the non-flaming combustion resulted in deaths post-exposure. 6). In general, How do low-density materials (such as polyurethane foam) burn compared to higher-density materials (cotton padding) of similar makeup? Int Anesthesiol Clin 33:181, Kimmerle G (1976) Toxicity of Combustion Products with Particular Reference to Polyurethane. The overall toxicity of the combined materials was higher, and the average concentrations of the gases throughout the tests were consistently higher than that of the individual materials in both flaming and non-flaming conditions. Do memory foam mattresses give off toxic fumes? 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. Asphyxiant or narcotic gases cause a decrease in oxygen supplied to body tissue, resulting in central nervous system depression, with loss of consciousness and ultimately death. This is unusual as this test method is usually well-ventilated and the results are not similar to reports of other authors (such as Levin et al. International Association for Fire Safety Science, Ravey M, Pearce EM (1997) Flexible Polyurethane foam. Isocyanate structure also affects the reactivity of the isocyanate group. New memory foam smell? 9). Insulation, like all building products, has an 'embodied' carbon footprint resulting from energy use during the manufacturing process. Heat, smoke and irritant gases may impair escape, increasing the risk of a lethal exposure to asphyxiant gases, andcan sometimes lung damage causes death in those managing to escape. 2007). The most notable and abundant of these was hydrogen cyanide which increased in yield from 700 to 1000C. However, unlike a real fire, the heat flux remains constant, and so when the oxygen concentration falls, the flame may be extinguished. 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. 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. 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. In ventilation controlled fires (such as those occurring in a room, buildingor other enclosure), the yields of these gases from the flaming combustion of polyurethane foams generally follow the same trend. 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). 14) (UK Fire Statistics 2013). Carbodiimides are produced by the reaction of isocyanates in the presence of a catalyst (such as phospholine oxides) (Scheme8) (Avar et al. The authors would like to thank Dr. Linda Bengtstrom for her contribution regarding the toxicity of isocyanates. During flaming combustion, many fire retarded flexible polyurethane foams showed similar or slightly higher toxic potency than the non-fire retarded foams in both well-ventilated and under-ventilated conditions. Ask Pablo: How Bad Is Memory Foam? NIST performed the experimental burn tests 1 on 4-inch (10-cm) thick by 4 ft x 4 ft (1.2 m x 1.2 m) wide polyurethane foam slabs. eds. (PDF) The fire toxicity of polyurethane foams - ResearchGate Primarily, isocyanates react with alcohols to produce urethane linkages in the polymer (Scheme1). 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. Since HCN is a major contributor to the fire toxicity of polyurethane foams, the mechanisms by which they decompose are vital in understanding why they produce large-quantities of HCN during under-ventilated burning. Polystyrene (EPS and XPS) has significant amounts of styrene offgassing early in life. Fire and Materials 23:p171185, Hull TR, Paul KT (2007) Bench-scale assessment of combustion toxicity-A critical analysis of current protocols. The authors acknowledged the complexity of the decomposition of the material but were able to summarise it effectively in a 5-step mechanism (Fig. LC50 values should be referenced to the fire condition under which they were measured. In a letter to the editor of the journal, Barbrauskas et al. The sample is spread evenly in a silica boat over a length of 800mm and fed into a tube furnace at a typical rate of 1gmin-1 with flowing airat a rate of 2-10 L min-1. Sensory and upper respiratory tract irritation stimulates the trigeminal and vagus nerve receptors in the eyes, nose, throat and upper respiratory tract causing discomfort, then severe pain. At 850C the yield of HCN was higher with 16mgg1 at ~2.0. The test conditions were designed so that the fire conditions met the ISO 19706 (2007) fire type 2 (well-ventilated flaming fire <0.75) and fire type 3b (post-flashover fire in large or open compartments ~2.0).
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