polyurethane foam, when burned gives off

The reported yields for the tests performed can be found in Table8. 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. 2011). As polyurethane foams have very low thermal inertia, application of heat or a small flame can be enough to ignite them. Some of these methods attempt to address the transition through the fire stages by monitoring the formation of toxic gases as a function of time, as the oxygen concentration falls, and the fire condition changes from well-ventilated to under-ventilated. For both materials there is a clear increasein yield from the well-ventilated to under-ventilated conditions. 1999). Experimental data reported a 28% recovery of DAT which supports the proposed decomposition mechanism. The full size ISO 9705 test resulted in well-ventilated flaming ( 0.260.5) due to the relatively large volume of air and relatively small sample size. statement and 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 56592 2012), and static tube furnace tests, such as the NF X 70100 (2006). HCN, in particular, contributes significantly to the overall fire toxicity of polyurethane foams. 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. This suggests that the nitrogen in the char will more readily form HCN, even when the flaming is well-ventilated. Aromatic isocyanates are more reactive than aliphatic isocyanates due to the electronic effects of the aromatic ring. This suggests that any amines formed would have reacted with isocyanates in the vapour phase to form ureas, some of which would have condensed to produce the observed waxy white substance. 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 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. During these tests, the PIR was set up as wall panels covered on two faces with aluminium foil. Allergy 63:p583591, Pitts WM (1995) The global equivalence ratio concept and the formation mechanisms of carbon monoxide in enclosure fires. (3) Polyurethane foam mattresses, dubbed "solid gasoline", can give off toxic fumes that may be linked to short- and long- term health conditions. The resulting substituted urea can then react with another isocyanate to produce a biuret linkage (Scheme4). From this, the library of data was sorted into categories of combustion/pyrolysis conditions, material/product, type of test animal and toxicological endpoint. 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. decomposition products will burn. The severity of the effects increases with dose (Hartzell 1993). This value decreased to 18mgg1 at ~2.0. Short chains with high functionality results in highly cross-linked polyurethane polymers which is characteristic of rigid foams. Privacy This char can decompose further, leaving behind a residue at >800C, to produce simple organic fragments and some polycyclic aromatic hydrocarbons (PAHs). For a fixed chamber volume (0.51m3), 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. 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. 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). 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. Biuret and allophanate bonds will decompose first between 100 and 125C. 23. The radiant heat flux in the ISO/TS 19700 apparatus has been measured (Stec et al. 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. However, the presence of Cu2O reduced the HCN generated by the flexible polyurethane foam by 70-90% at low temperatures. ISO 19706 (2011) Guidelines for assessing the fire threat to people. (1990) also reported increased HCN yields when the sample was allowed to smoulder before flaming in similar apparatus as above. 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 fire toxicity of a material can also be expressed as a material-LC50, which in this case is the specimen mass M of a burning polymeric material which would yield an FED equal to one within a volume of 1m3. Garrido and Font (2015) reported two main steps in the inert-atmosphere decomposition of flexible polyurethane foams. . The steady state tube furnace (ISO/TS 19700 2013), shown in Fig. Reaction between an isocyanate and an alcohol to produce a urethane, Reaction of an isocyanate with water to produce a carbamic acid which decomposes to produce an amine and carbon dioxide, Reaction of an isocyanate with an amine to produce a urea, Reaction of an isocyanate with a urea to produce a biuret linkage, Reaction of a urethane with an isocyanate to produce an allophanate linkage. Further reactions occur with amines, water, ureas, urethanes and even other isocyanates to produce a diverse range of functional groups including urethanes, ureas, isocyanurates, carbodiimides and uretdiones. DiNenno et al., eds.). 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. This makes the isocyanate functional group highly reactive towards nucleophiles with an available hydrogen. However, many people fail to escape from fires because of the incapacitating effect of smoke (obscuring visibility) and its irritant components which cause pain, preventing breathing and escape or reason death occurred. Based on the temperature of the test, the yields of HCN are extremely low when compared with the CO yields. The first step is the decomposition of the urethane bonds to release and volatilise isocyanates up to 300C, with long chain alcohols being left behind in the condensed phase, followed by the alcohols degrading at around 400C. Taking this into consideration, the reported yields of isocyanates, aminoisocyanates and amines are still relevant, as the results of Blomqvist et al. Work by Guo et al. 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. TDI is primarily used in the production of flexible foams, which are used in the furniture and interior industries. The yields of toxic products followed the expected trend of being higher in the under-ventilated conditions. Routes of entry in this case are inhalation, ingestion (saliva), and skin absorption. At higher temperatures the decomposition of the foams produced increasing amounts of HCN from 600 to 900C, followed by a sharp rise between 9001000C. DiNenno et al. An equation has been developed for the estimation of the FED for lethality from the chemical composition of the environment in the physical fire(such as the bench-scale methods described in the following section) model taken from ISO 13344 (1996) and uses gas-LC50 values for lethality to provide referencetoxicity data for the individual gases to calculate toxic potency, based on rats exposed for 30min. Burning foam will emit mainly carbon monoxide, carbon dioxide and small traces of other toxic gases, such . 6). . Polymer Degradation and Stability 93:p20582065, Tewarson A (2002) SFPE Handbook of Fire Protection Engineering, 3rd ed. The PIR at 1.75 resulted in 15% of the fuel nitrogen being recovered as HCN. 2008; Kaplan 1987b). Humans may react differently than animals exposed to toxic materials. Terence Richard Hull. The yields of some of the most toxic gases from unwanted fires (such as CO, HCN and some organic irritants) have been demonstrated to be directly related to the combustion conditions (Purser 2002). 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). Polyurethane and polyisocyanate both release polyols and isocyanates during blowing, but the rates diminish rapidly over time as the product cures, provided they dialed in the temps & chemical mix correctly. Additionally, the self-addition of isocyanates to produce isocyanurates (v in Fig. (2011) developed a mechanism based on both condensed and gas-phase decomposition in air. When the black char was burned at 600C, it yielded 14.95mg of HCN (65mg per gram of char) and the yellow oil yielded 21mg per gram of oil. A polyether polyol (i) and a polyester polyol (ii). 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. TRH wrote the fire toxicity section of the manuscript. At sufficiently high concentrations, or when attached to submicron particles, such as soot, most irritants can penetrate deeper into the lungs, causing pulmonary irritation effects which may cause post-exposure respiratory distress and death, generally occurring from a few hours to several days after exposure, due to pulmonary oedema (flooding of the lungs) (ISO 13571 2007). When =1 the theoretical amount of air is available for complete combustion to carbon dioxide (CO2) and water. A review by Paabo and Levin (1987) found that there is no difference in the decomposition products of rigid and flexible polyurethane foams at high temperatures regardless of their differing degradation mechanisms at lower temperatures. 11) ultimately giving well-ventilated flaming. National Fire Protection Association, Quincy, MA, pp 5482, Guo X, Wanga L, Zhanga L, Lia S, Hao J (2014) Nitrogenous emissions from the catalytic pyrolysis of waste rigid polyurethane foam. 2005; Blomqvist & Lonnermark 2001). In a real fire, involving cycles of growth and decay of flaming combustion, the resulting yields of HCN from the combustion of polyurethane foams are likely to be higher than predicted in some bench-scale methods as a result of this two-step decomposition mechanism. Anal Bioanal Chem 387:p219236, Herrington R, Hock K (1998) Flexible Polyurethane Foams, 2nd edn. (1972). Early work by Voorhees (1975) identified what they described as extreme toxicity of the combustion products of a phosphate fire retarded polyurethane foam. The widespread use of flexible polyurethane foams in furniture and other upholstery, where they are usually covered in some kind of fabric has prompted some authors to investigate the effects of covering the foam on the yield of toxic products. The authors asserted that fire retarding flexible polyurethane foam did not increase its acute or chronic toxicity when compared to non-fire retarded flexible foam. Busker RW, Hammer AH, Kuijpers WC, Poot CAJ, Bergers WWA, Bruijnzeel, PLB (1999) Toxicity testing of combustion products of polyurethane and polyvinylchloride. 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 inISO 56592 2012, andshownschematically in Fig. The interior of large flames are always under-ventilated, because oxygen cannot penetrate the flame. The NFX generates data intermediate between the well-ventilated and under-ventilated fire conditions. NBSIR 822532. While the data presented is a useful compilation of toxic potency data from the available literature before 2004, the report does not take into consideration the conclusions of individual authors, the exact specifics of the test condition, and the validity of the results. At 1000C the hydrogen cyanide produced accounted for a range of between 3.8 and 7.3% by weight. Data from large scale fires in enclosures, such as a room, shows much higher levels of thetwo of the major toxicants, carbon monoxide (CO) and hydrogen cyanide (HCN) under conditions of developed flaming (Andersson et al. The most commonly reported adverse health effects after airborne isocyanate exposure is asthma due to sensitisation (Piiril et al. This was enough to cause deaths both during and post-exposure. National Fire Protection Association, 82, p 161, Vilar WD (2002) Chemistry and Technology of Polyurethanes - Chapter 1. 9). 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 half-scale ISO 9705 experiments showed a wider range of ventilation conditions up to ~2.0. Their development continued commercially in Germany, eventually leading to a global multibillion dollar industry (Vilar 2002). 2012). Fire and Materials 31:p327354, Schnipper L, Smith-Hansen ES (1995) Reduced combustion efficiency of chlorinated compounds, resulting in higher yields of carbon monoxide. 1992), shown in Fig. Memory foam is a type of polyurethane foam. 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. The flexible foam produced ~175mgg1 of CO and 5mgg1 of HCN. to FED. The effect of asphyxiants and deep lung irritants depend on the accumulated doses, i.e. 2008), where inhaled isocyanates rapidly form conjugates with epithelial lung cell proteins (Wisnewski et al. Babrauskas V, Lawson JR, Walton WD, Twilley WH (1982) Upholstered Furniture Heat Release Rates Measured with a Furniture Calorimeter. However, when the TDI was unable to enter the pyrolysis zone, the slower, irreversible decomposition to diaminotoluene (DAT) would occur. Interflam Conference Proceedings. In some bench-scale apparatus the heat flux is constant, and often insufficient to sustain flaming at such low oxygen concentrations; further, an unknown quantity of fresh air bypasses the fire plume, so the ventilation condition, and hence, remains undefined. Carbon monoxide binds to the haemoglobin in red blood cells resulting in the formation of carboxyhaemoglobin (COHb), with stability 200 times greater than that of oxyhaemoglobin, impeding the transport of oxygen from the lungs to the cells in the body. (P.J. However, the lower yields can be attributed to the fact that the cone calorimeter is a well-ventilated scenario, estimated as ~0.7 (Schartel & Hull 2007). CO yields are generally very low for well-ventilated conditions (in the absence of halogens) but increase considerably under-ventilated combustion conditions. These processes occur at around 300C with the precursor chemicals including TDI, MDI, HDI, polyols (both polyether and polyester-polyols) and aromatic amines. The chemical additives to the polyurethane are said to give off a distinct chemical odor that lessens after adequate ventilation. In the large scale test room, the sample smouldered for 1.5 to 2h, resulting in a HCN yield of 1.03mgg1. Around 1015% of the nitrogen in the polymer can be converted into HCN with some being released in isocyanates, aminoisocyanates and amines in the fire effluent. Thermal decomposition of polyurethanes is usually the reverse of polymerisation, resulting in the formation their precursor functional compoundsdiisocyanates, diamines and dihydroxy compounds. This step dramatically reduced fire deaths, which was considered a triumph at the time. 4)). This is when flame retardant chemicals were added to the foam or coverings to stop the furniture from burning so ferociously.

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