Biuret and allophanate bonds will decompose first between 100 and 125C. Acrolein and formaldehyde are formed especially from cellulosic materials under non-flaming decomposition conditions, but products of vitiated combustion contain other organic irritants. As the toxic product yields of polyurethane foams are directly related to the ventilation conditions, so is the materials LC50 value. SP Swedish National Testing and Research Institute, Bors, Hietaniemi J, Kallonen R, Mikkola E (1999) Burning characteristics of selected substances: Production of heat, smoke and chemical species. 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. 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. Work by Ravey and Pearce (1997) on the decomposition of a polyether based flexible polyurethane foam suggested that up to 360C the decomposition of the foam was achieved by two main mechanisms. 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. 1981), probably because of increased use of nitrogen-containing synthetic polymers. (2011) developed a mechanism based on both condensed and gas-phase decomposition in air. True. In many studies (such as those by Stec and Hull (2011), Purser and Purser (2008a) and Blomqvist et al. Table1 shows the relative reactivity of isocyanates with nucleophiles at 25C without the presence of a catalyst. Andersson B, Markert F, Holmstedt G (2005) Combustion products generated by hetero-organic fuels on four different fire test scales. Fire Research Notes 951:p117. The toxic product yields may be quantified from the gas concentrations and mass feed rate during the steady state burn period. Provided by the Springer Nature SharedIt content-sharing initiative. VOCs have the ability to vaporize, or off-gas, at room temperature. Garrido and Font (2015) reported two main steps in the inert-atmosphere decomposition of flexible polyurethane foams. thesis, Virginia Tech, p6-40, ASTM E 1354 Standard Test Method for Heat and Visible Smoke Release Rates for Materials and Products Using an Oxygen Consumption Calorimeter, ASTM E 662 Standard Test Method for Specific Optical Density of Smoke Generated by Solid Materials. The general approach, described in ISO 13571 (2012), is to ensure that the available safe escape time (ASET) before escape routes become obscured by smoke and/or filled with toxic gases, exceeds the required safe escape time (RSET). Work by Guo et al. The process of . (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. PDF Polyurethanes and Thermal Degradation Guidance The most commonly reported adverse health effects after airborne isocyanate exposure is asthma due to sensitisation (Piiril et al. PML 1998-A97. While well-ventilated fire scenarios are routinely used for assessment of flammability, because the object is to stop the fire growing to the out of control stage, where fire toxicity is concerned, the important fire stages are under-ventilated. The polyurethanes used were elastomers based on TDI, which could potentially have differing decomposition mechanisms to their foam counterparts. CO also combines with myoglobin in the muscle cells, impairing diffusion of oxygen to cardiac and skeletal muscles (Purser 2008b). 1982) to that of a large scale test room. 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. National Bureau of Standards, Gaithersburg, MD, Levin BC, Paabo M, Birky MM (1983b) Interlaboratory evaluation of the 1980 version of the national bureau of standards test method for assessing the acute inhalation toxicity of combustion products, NBSIR 832678, National Bureau of Standards, Gaithersberg, MD, Levin BC, Paabo M, Fultz ML, Bailey CS (1985) Generation of Hydrogen Cyanide from Flexible Polyurethane Foam Decomposed under Different Combustion Conditions. The Steady state tube furnace apparatus, ISO/TS 19700. Top of Page. Material composition, temperature and oxygen concentration are normally the most important. The mechanisms of decomposition are well understood and the decomposition products of both rigid and flexible polyurethane foams are very similar at high temperatures. Do memory foam mattresses give off toxic fumes? Irritant gases cause pain and breathing difficulties, leading to incapacitation, such that the victim can no longer effect their own escape (ISO 13571 2012). The presence of both amines and water in the decomposition products of polyurethane foams are discussed in later sections. McKenna, S.T., Hull, T.R. Since serious fires involving the use of these materials have occurred on several ships, the United States Coast Guard has issued a Navigation and Vessel Inspection Circular No. 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. 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. 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). Three Massachusetts Home Fires Linked to Spray-Foam Installation The severity of the effects increases with dose (Hartzell 1993). Similarly, the polyether based foam produced 15.1mgg1 to 28.1mgg1. 7) (Avar et al. Terence Richard Hull. Isocyanate derived functional groups that cross-link polyurethane chains i) biurets ii) allophanates. Therefore, in certain conditions, polyurethanes foams can reach their auto-ignition temperature and ignite which will significantlyalter the effect the decomposition mechanisms and resulting products. To a lesser extent, parameters such as temperature and oxygen concentration also affect the yields of toxic products. 3 FIRE INVESTIGATOR REVIEWS Flashcards & Practice Test | Quizlet The authors also noted that the presence of aldehydes was detected during the flaming combustion of the flexible foam, albeit in extremely low yields. As fires grow, they become ventilation controlled, and fires in enclosures such as buildings rapidly change from well-ventilated to under-ventilated. Similarly, Busker et al. HCN yields reported in under-ventilated conditions vary depending on the composition of the material; with flexible foams producing less than rigid foams and polyisocyanurates producing the most overall. Cite this article. Toxic product yields frommaterials involved in fires depend on a number of factors. Studies have found that infant mattressesespecially those made with polyurethane foam, which contains the hydrocarbon tolueneare a major off-gassing culprit (Boor, et. Avar G, Meier WU, Casselmann H, Achten D (2012) Polymer Science: A Comprehensive Reference, Polymer Science: A Comprehensive Reference, 10, p411-441. Woolley WD, Wadley AI, Field P (1972) Studies of the thermal decomposition of flexible polyurethane foams in air. 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 chemical additives to the polyurethane are said to give off a distinct chemical odor that lessens after adequate ventilation. The toxic hazards associated with fire and the inability of victims to escape from fire atmospheres may be considered in terms of major hazard factors: heat, smoke and toxic combustion products (Hartzell 1993). When tested with the polyester covering the polyurethane, the yield of HCN during flaming combustion was higher than that of just the polyurethane foam on its own. Ask if the mattress materials are generally free of VOC and HAPs. UPDATED 8/16/2011 The Massachusetts Division of Fire Safety (DFS) is investigating the causes of three house fires that were ignited while insulation contractors were installing spray polyurethane foam. Summing these contributions generates a fractional effective dose (FED). Foams Under Laboratory Conditions, Fire Research Note, No 1039. 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. Fire Res 1:p1121. The cribs used in the ISO 9705 tests were constructed from PIR sticks which burned rapidly, albeit with minimal damage to the room. 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. (2007)), the sample is raised to a fixed furnace temperature, which is further increased in the gas phase during flaming combustion. Allergy 63:p583591, Pitts WM (1995) The global equivalence ratio concept and the formation mechanisms of carbon monoxide in enclosure fires. 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). 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. 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). As polyurethane foams have very low thermal inertia, application of heat or a small flame can be enough to ignite them. Preliminary calculations suggested that 27% of the TDI should be recovered as DAT. This char can decompose further, leaving behind a residue at >800C, to produce simple organic fragments and some polycyclic aromatic hydrocarbons (PAHs). 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. 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. By using this website, you agree to our A summary of these structures is shown in Fig. 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. For any larger fire there will always be a significant yield of CO, HCN (from nitrogen containing materials), hydrocarbons and smoke. Early work by Woolley et al (1975) indicated that the decomposition of polyurethanes up to around 600C resulted in the volatilisation of fragmented polyurethane and subsequent release into a nitrogen rich yellow smoke, containing partially polymerised isocyanates and droplets of isocyanate from the foam. The 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. Stec and Hull (2011) assessed the fire toxicity of building insulation materials using a steady state tube furnace asdescribed in ISO/TS 19700 (2013). 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. These reactions are accelerated in the presence of oxygen, which reduces the temperature of the decomposition steps. p 111711128. In some cases the effluent continues to burn as it emerges from the chamber, (secondary flaming in Fig. 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). Spray foam can potentially generate toxic emissions under these circumstances. Before you take it for a test drive, make sure to give your new mattress time to off-gas in a well-ventilated environment. CO yields are generally very low for well-ventilated conditions (in the absence of halogens) but increase considerably under-ventilated combustion conditions. Further decomposition occurred about 600C with the fragmentation of the yellow smoke, primarily into hydrogen cyanide and small quantities of acetonitrile, acrylonitrile and benzonitrile. Again, above 600C the compound and any yellow smoke present was decomposed into smaller volatile fragments. A polyether polyol (i) and a polyester polyol (ii). Equation3 uses a similar principle to equation1 to estimate the combined effect of all irritant gases. 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). Two mechanisms have been identified for the toxic effects of cyanide. The full-scale test showed good accordance with the SSTF data considering the inherent unreliability of large-scale testing. In particular, the ventilation condition has a critical effect on the yield of the two major asphyxiants, carbon monoxide and hydrogen cyanide.
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