Humans may react differently than animals exposed to toxic materials. Additionally, the self-addition of isocyanates to produce isocyanurates (v in Fig. 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). Whether one or other of these mechanisms predominates, or their interrelationship, remains unclear. DiNenno et al., eds.). 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. This agrees with the fact that oxidation of NH3 and HCN to NO (and NO2, although it was not analysed in these experiments) would occur more readily during well-ventilated burning. Fire Safety Science - Proceedings of the First International Symposium, p1111-1122, Markets and Markets report (2011) Methylene Diphenyl Diisocyanate (MDI), Toluene Diisocyanate (TDI) and Polyurethane Market (2011 2016): Markets and Markets CH 1596, July 2011, Marsh ND, Gann RG (2013) Smoke Component Yields from Bench-Scale Fire Tests: 4. 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. The applied heat flux must be large enough for burning to continue at oxygen concentrations as low as 5%. Animal studies provide most of what we know about the dangerous effects of toxic substances. At this temperature around one third of the compounds mass was lost as volatile products, and the regenerated alcohol products were mainly present in the residue of the sample. 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. Nitrogen dioxide dissolves rapidly in water to form nitric and nitrous acid. The relationship between equivalence ratio and yields of CO and other products has been studied in detail for a wide range of materialsduring flaming combustion using two small-scale apparatus designed specifically for this purposethe 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). The authors acknowledged that they did not include isocyanates in their calculations. p 1-30. Bench-scale methods used for generating toxic effluents from polyurethane foams have met with controversy. In general, How do low-density materials (such as polyurethane foam) burn compared to higher-density materials (cotton padding) of similar makeup? However, in the field of combustion toxicity testing, this under-ventilated burning is the most difficult to create using bench-scale apparatus. The initial decomposition of the foam, at >300C, results in the volatilisation of isocyanates, amines and Woolleys yellow smoke, leaving behind polyols in the condensed phase. The fire department was not immediately called, so the oil burned completely. Therefore, the products of decomposition can be predicted from the composition of the polymer. The reported yields were extremely low for both CO and HCN, as the NBS smoke chamber apparatus is a well-ventilated fire scenario reported to give low HCN yields (Table6). Higher temperatures resulted in the volatilisation of most of the polyurethane precursors via the formation of lower molecular weight compounds. Isocyanurate rings are the most thermally stable in an inert atmosphere and decompose between 270 and 300C. The most notable and abundant of these was hydrogen cyanide which increased in yield from 700 to 1000C. The steady state tube furnace (ISO/TS 19700 2013), shown in Fig. The general approach in generating toxic potency data from chemical analysis is to assume additive behaviour of individual toxicants, and to express the concentration of each as its fraction of the lethal concentration for 50% of the population for a 30min exposure (gas-LC50). The three-compartment test consisted of a 2.43.72.4m burn room, a 2.44.62.4m corridor and a 2.43.72.4m target room where samples would be taken. 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. In general conversion efficiencies are high for halogen acid gases. After the initial stages of inert-atmosphere thermal decomposition where the polymer precursors are reformed and volatilised, the decomposition products tend to fragment into smaller molecules. Ask if the mattress materials are generally free of VOC and HAPs. 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. Foam: Fire Hazard and Fire Barrier | Monolithic.org The yields of acid gases and nitrogen-containing products depend upon the proportion of the appropriate elements in the materials burned and the efficiency of conversion. The polyurethane market was estimated to be worth $33 billion in 2010 and is expected to continue to grow to over $55 billion by 2016. 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. From this, the library of data was sorted into categories of combustion/pyrolysis conditions, material/product, type of test animal and toxicological endpoint. It forces combustion by driving the sample into a furnace of increasing heat flux at a fixed rate, so that, by running several tests with the same material with different ventilation conditions, each fire stage can be replicated by steady state burning. Polyurethanes are named from the presence of theurethane (also known as carbamate) functional group (Fig. The samples were heated at 800C in a static tube furnace, with the effluent being cooled to <50C before entering an exposure unit. 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. Is Memory Foam Toxic? | Sleep Foundation Investigations by Hertzberg et al. 1982), and a three . However, this did not take into consideration the incapacitating effects of the release of irritant gases. A more recent review, by Levchik and Weil (2004), assessed the decomposition, combustion and fire-retardancy of polyurethanes. 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). 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. 1982), the authors exposed male Fisher 344 rats in a 200L exposure chamber to the fire effluent from the flaming and non-flaming combustion of both materials. 3) (Aneja 2002). The reported yields for the tests performed can be found in Table8. In particular, reports that used non-standard tube furnace apparatus lacked sufficient information about the conditions of the experiment and as such were not included. Fire and Polymers II: Materials and Tests for Hazard Prevention 599:p498517, Chun BH, Li X, Im EJ, Lee KH, Kim SH (2007) Comparison of Pyrolysis Kinetics between Rigid and Flexible Polyurethanes. 6 Sources of Toxic Chemicals (VOCs) in Your Home 2008) and is 40kWm2 in the centre of the furnace at 650C and 78kWm2 at 825C. For example, polyurethane foam, when burned, gives off cyanide gas. 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. Common polyurethane functional groups i) urethane ii) urea iii) carbodiimide iv) uretdione v) isocyanurate. Chem Co., Dow, Hertzberg T, Blomqvist P, Dalene M, Skarping G (2003) Particles and Isocyanates from Fires. Is Polyurethane Foam Toxic, And Should You Avoid it? - The Safe Parent A "combustion modified high resilience" flexible polyurethane foam (CMHR-PUF) and a polyisocyanurate (PIR) foam were analysed a steady state tube furnace apparatus. 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). The authors noted that the yields of the toxicantsproduced an atmosphere in the tests which fell well below their Immediately Dangerous to Life and Health (IDLH) values. When formed at the site, there is a potential for a completed-operations exposure. A large number of studies have been performed over the last 50years to understand the thermal decomposition of polyurethane materials, and as a result of this the mechanism of their decomposition in inert-atmospheres is fairly well understood. Polyvinyl chloride, formaldehyde, boric acid, antimony trioxide and different types of petrochemicals. Journal of Applied Polymer Science 63:p4774, Rein G, Lautenberger C, Fernandez-Pell AC (2006) Application of Genetic Alogorithms and Thermogravimetry to Determine the Kinetics of Polyurethane Foam in Smoldering Combustion. 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). The severity of the effects increases with dose (Hartzell 1993). to FED. J Allergy Clin Immunol 104:p341347, Woolley WD, Fardell PJ (1977) The prediction of combustion products. 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. Generalised decomposition mechanism for polyurethane foams both in nitrogen and in air. 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.
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