The polyurethanes used were elastomers based on TDI, which could potentially have differing decomposition mechanisms to their foam counterparts. In particular, the ventilation condition has a critical effect on the yield of the two major asphyxiants, carbon monoxide and hydrogen cyanide. 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. These polyols will fragment and volatilise as the temperature increases, leaving behind a char (>600C). Taking into consideration the issues with repeatability of large-scale testing, the authors asserted that the similar trend in HCN yields supported the good relationship between the tube-furnace and large-scale results. At 650C, the yield of HCN from the CMHR-PUF increased up to ~2.0 where it reached a peak of 14mg of HCN per gram of polymer burned. Intermediate between these two approaches are those that can produce quasi-steady combustion conditions, such as the cone calorimeter (ISO 56601 2002) with non-standardised controlled atmosphere attachment (CACC), and the fire propagation apparatus (FPA) (ISO 12136 2011). FED model from ISO 13571, Equation It has been designed to generate data for input to fire hazard assessments, using the methodology in ISO 13344 (1996) and ISO 13571 (2012), particularly in relation to the ISO fire stages. Fire and Materials 11:p129, Paul KT, Hull TR, Lebek K, Stec AA (2008) Fire smoke toxicity: The effect of nitrogen oxides. The reaction of a urethane with another isocyanate will produce an allophanate (Scheme 5). 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. 2007). 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. The study also suggested that any remaining isocyanates residue would react with themselves to produce polycarbodiimides, thus anchoring the isocyanate precursors in the condensed phase until around 600C, where they would fragment. The applied heat flux must be large enough for burning to continue at oxygen concentrations as low as 5%. \( \phi =\frac{actual\; fuel\;to\; air\; ratio}{stoichiometric\; fuel\;to\; air\; ratio} \). 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. 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. Paabo and Levin (1987) reviewed the literature of the toxic product generated by the combustion of rigid polyurethane foams. The results indicated that the formation of the precursor, TDI, was much faster and preferable to depolymerisation when the volatile compounds could escape. At 850C the yield of HCN was higher with 16mgg1 at ~2.0. 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. 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). It is difficult to draw more general conclusion from this work because the fuel-to-air ratio was not quantified, and the degree of mixing of fresh air and fire effluent, in the exposure chamber, is unknown. When polyurethane and polystyrene burn, they create a very smoky fire that . (2007)), the sample is raised to a fixed furnace temperature, which is further increased in the gas phase during flaming combustion. STM would like to acknowledge the University of Central Lancashire for provision of a studentship. Resources & Documents Library McKenna, S.T., Hull, T.R. 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. Using a cup furnace with a 200L sampling chamber (identical in design to the one used in the smoke chamber experiments), a 3.88g sample of foam was heated to just below its ignition temperature (370C) which yielded <1mgg1 HCN. The presence of oxygen in the atmosphere directly interacts with the solid phase, which accelerates decomposition. Cyanide gas. Biuret and allophanate bonds will decompose first between 100 and 125C. The results from the SSTF and FPA show the best agreement with those from the full and 1/3 scale ISO room for both materials under a range of 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. However, when >2.0 the yield of HCN decreased, falling to 10mgg1 at ~2.75. (2013) further supported the presence of two separate decomposition mechanisms for flexible foams. 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 use of 13C labelling in this case allowed the authors to confirm that the nitrogenous compounds, HCN and organonitriles, originated from the thermal fission of the aromatic rings with the nitrile carbon being the 2-,4- or 6- carbon of the MDI ring. Based on this data, the HCN recovery fraction was calculated for both materials. In 1975, California passed flammability standards known as Technical Bulletin 117 (TB117), which required polyurethane foam and fabrics produced in state to be treated with flame-retardant chemicals . A detailed understanding of the thermal decomposition chemistry of polyurethane foams is necessary in order to relate the toxicants generated during bothflamingand non-flaming combustion of the polymer to its structure. However there was significant scattering of the results with both high and low outliers (26mgg1 at 1.22 and 9mgg1 at 1.95). Reliable rate of heat release, fire effluent toxicity and smoke generation data are all essential components of such an assessment. The difficulty of replicating the conditions of fully developed under-ventilated flaming on a bench-scale is caused by several practical problems. P.J. Fumes Tiny particles are produced from heating, volatilization, and condensation of metals (examples: zinc oxide fumes from welding of galvanized metal). The authors noted that in both the flaming and non-flaming combustion of the polyurethane foam, the concentrations of toxicants did not reach high enough concentrations to predict deaths. Aromatic diisocyanates ortho- or para- to one another will have an activating effect on each other, thus increasing their reactivity. This is true of ALL polyurethane foam since it is an organic material, just like wood or cotton fabric. This equation only relates to lethality, or cause of death. Alongside the experiments performed in the steady state tube furnace, the PIR was also investigated in a half scale ISO 9705 room-corridor test and in a full size ISO 9705 (1993) room. Secondary air is added in a mixing chamber to give a total gas flow of 50Lmin1. 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. Hietaniemi et al. The methods of assessment of fire toxicity are outlined in order to understand how the fire toxicity of polyurethane foams may be quantified. 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. Hexamethylene diisocyanate (HDI) (i), 1,5-naphthalene diisocyanate (NDI) (ii) and isophorone diisocyanate (IPDI) (iii). Cookies policy. From this, the library of data was sorted into categories of combustion/pyrolysis conditions, material/product, type of test animal and toxicological endpoint. It is inexpensive and easy to install, however, it is a severe fire risk and requires a thermal barrier to make it safe. Results from these burn tests are used for comparison with the model developed to simulate flame spread, heat fluxes, and smoke development over time (Figure 1). Substituted aromatics containing electron withdrawing groups further increase the reactivity of isocyanates by increasing the partial positive charge on the isocyanate carbon via a resonance withdrawing effect. The difference with other polyurethane foams is that memory foam also contains added chemicals that increase its viscosity and elasticity, hence its alternate name, viscoelastic foam. The lowest temperature at which a liquid will give off vapors at a sufficient rate to support a momentary flame across its surface is known as its: . Full-scale fires simultaneously involve different fire stages in different places, which are changing with time. (1991a) compared a number of test methods. Aromatic diisocyanates, which are commonly used in the production of polyurethanes, have a slightly more complicated chemistry compared to monoiscyanates due to the electronic effects of two isocyanate groups. Unlike carbon monoxide which remains primarily in the blood (as COHb), the cyanide ion is distributed throughout the extra-cellular fluid of tissues and organs (ISO 13571 2007). 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). combustion modified high resilience polyurethane foam, Alarie Y (2002) Toxicity of Fire Smoke. statement and Woolley WD, Fardell PJ, Buckland IG (1975) The Thermal Decomposition Products of Rigid Polyurethane. The main asphyxiants, carbon monoxide and hydrogen cyanide have been widely studied and are the best understood (ISO 13571 2007). Since then, Blais and Carpenter (2015) investigated a flexible polyurethane foam with and without a chloro phosphate (tris-dichloro-propyl phosphate TDCPP) fire retardant using a smoke box (ISO 56592 2012) to assess the toxicity. Using polyurethane indoors can expose you to fumes with a number of potential side effects. 9). 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. The half-scale ISO 9705 experiments showed a wider range of ventilation conditions up to ~2.0. al, 2014). In particular, the ventilation condition has a . This suggests that the nitrogen in the char will more readily form HCN, even when the flaming is well-ventilated. The detection of the amino MDI derivative in the tar further supports the literature reports of a secondary decomposition mechanism where isocyanates trapped in the condensed phase are converted irreversibly into their amine derivatives. Toxicology 47:165170, Kaplan HL, Grand AF, Hartzell GE (1984a) Toxicity and the smoke problem. 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. 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. Draeger tubes), conventional or Fourier transform infrared spectroscopy (FTIR) gas analysis, despite significant problems of reproducibility. Fire Safety Journal 43:243251, Piiril PL, Meuronen A, Majuri ML, Luukkonen R, Mntyl T, Wolff HJ (2008) Inflammation and functional outcome in diisocyanate-induced asthma after cessation of exposure. Does Polyurethane Foam Give Off Toxic Fumes? Additionally, the amount of CO generated for both materials began to taper off at 1.2-2.0 as the available oxygen becomes so low that the generation of CO becomes limited, while the yield of HCN continues to increase with equivalence ratio and temperature. The cribs used in the ISO 9705 tests were constructed from PIR sticks which burned rapidly, albeit with minimal damage to the room. Does the foam give off toxic fumes if burned? (1972) noted that the yellow smoke was produced up to around 600C, where it would then decompose to give a family of low molecular weight, nitrogen containing products including hydrogen cyanide, acetonitrile, acrylonitrile, pyridine, and benzonitrile. The average combined yield of isocyanates recovered was 0.869mgg1 and the average yield of amines and aminoisocyanates was 0.321mgg1. Conversely, nitric oxide gas at low concentrations(~20 ppm) has been used to aid breathing in the treatment of respiratory disorders (Kavanagh & Pearl 1995). 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. 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. 23. 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. Further decomposition occurred about 600C with the fragmentation of the yellow smoke, primarily into hydrogen cyanide and small quantities of acetonitrile, acrylonitrile and benzonitrile. Additionally, HCN yields in both flaming and non-flaming conditions increases with temperature. More recent work by Shufen et al. Based on the temperature of the test, the yields of HCN are extremely low when compared with the CO yields. ISO 19706 (2011) Guidelines for assessing the fire threat to people. Equation According to Tim Rodrique, the director of the DFS, investigators suspect that the fires were caused by the exothermic reaction that results from the mixing of the two chemicals used to make . 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). Further to this, a similar pattern began to emerge in the injuries of fire victims (Fig. Polymer Degradation and Stability 93:p20582065, Tewarson A (2002) SFPE Handbook of Fire Protection Engineering, 3rd ed. In contrast to the relativelywell-defined effects of asphyxiants, the effects of exposure to irritants are more complex. 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. 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. Gaithersberg, MD, Babrauskas V, Twilley WH, Janssens M, Yusa S (1992) Cone calorimeter for controlled-atmosphere studies. (2014) on the catalytic decomposition of rigid polyurethane foam waste showed that ammonia, hydrogen cyanide and both nitrogen oxide and nitrogen dioxide were produced at temperatures up to 1100C. This step dramatically reduced fire deaths, which was considered a triumph at the time. Combustion Science and Technology 183(7):p627644, Saunders JH (1959) the Reactions of Isocyanates and Isocyanate Derivatives at Elevated Temperatures. Terms and Conditions, California Privacy Statement, 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. 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. A sample of rigid polyurethane foam was heated in a static tube furnace with an air flow of 50mlmin1 at a range of temperatures from 600 to 1200C and the yield of HCN was quantified. The effects range from tears and reflex blinking of the eyes, pain in the nose, throat and chest, breath-holding, coughing, excessive secretionof mucus, to bronchoconstriction and laryngeal spasms (Purser 2008b). 14) (UK Fire Statistics 2013). While several authors work has focused primarily on the nitrogenous products of decomposition, other publications have focused on the production of other compounds such as carbon monoxide. Studies have found that infant mattressesespecially those made with polyurethane foam, which contains the hydrocarbon tolueneare a major off-gassing culprit (Boor, et. Ann occup Hyg 19:269273, Levchik SV, Weil ED (2004) Thermal Decomposition, combustion and fire-retardancy of polyurethanes - a review of the recent literature. Fire gases contain a mixture of fully oxidised products, such as carbon dioxide (CO2), partially oxidised products, such as carbon monoxide (CO) and aldehydes, fuel and fuel degradation products, such as aliphatic or aromatic hydrocarbons, and other stable gas molecules, such as hydrogen halides (HCl, HBr) and hydrogen cyanide (HCN) (Kaplan et al. Other common diisocynates include hexamethylene diisocyanate (HDI), 1,5-naphthalene diisocyanate (NDI) and isophorone diisocyanate (IPDI) (Fig. A comprehensive review of fire retardants and their use in polyurethane foams was published by Singh and Jain (2009). Polymer-Plastics Technology and Engineering 45:p95108, Singh H, Jain AK (2009) Ignition, Combustion, Toxicity, and Fire Retardancy of Polyurethane Foams: A Comprehensive Review. 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. The chemical additives to the polyurethane are said to give off a distinct chemical odor that lessens after adequate ventilation. 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. 1981), probably because of increased use of nitrogen-containing synthetic polymers. Polyurethane and other organic foam materials are finding increased use on vessels because of their excellent insulating properties and light weight. Instead polyureas were detected in the vapour phase and also in the condensed phase as a waxy, insoluble white substance. Hydrogen chloride (HCl) and hydrogen bromide (HBr) are strong acids which dissociate entirely in water. This makes foam mattresses very harmful. The polyester fabric produced 9293mgg1 of CO when burned with very little difference in the flaming or non-flaming conditions. Using the methodology in ISO 13344, the authors also calculated the fractional effective dose (FED) of the individual toxicants sampled. What does polyurethane foam give off when burned? The polyisocyanurate, on the other hand, produced slightly more HCN than the rigid foam (17mgg1 vs 12mgg1). A summary of the bond decomposition temperatures in polyurethanes is shown in Table2 (Gharehbagh & Ahmadi 2012). Before you take it for a test drive, make sure to give your new mattress time to off-gas in a well-ventilated environment. Some methods have proved incapable of properlyreplicating 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. Three Massachusetts Home Fires Linked to Spray-Foam Installation TNO Prins Maurits Laboratory, The Netherlands. NBSIR 822604. 2 Taking this into consideration, the reported yields of isocyanates, aminoisocyanates and amines are still relevant, as the results of Blomqvist et al. When a liquid fuel gives off enough vapors so that it can be . However, spray foam insulation is a highly energy-efficient product and quickly offsets its manufacturing footprint. 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). In some cases the effluent continues to burn as it emerges from the chamber, (secondary flaming in Fig. This can be explained by the fragmentation of nitrogen containing organics in the flame and in the effluent, as suggested bystudies of the inert-atmosphere decomposition of polyurethane materials. Each method is described briefly in the following section. 1992), shown in Fig. Toxic Materials in Foam Mattresses? Are We Safe? Rubber Chemistry and Technology 32(2):p337345, Article (1981) on polycarbodiimides and polyureas enabled the determination of the source of the organonitriles and HCN during thermal decomposition. 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. The flexible foam produced ~175mgg1 of CO and 5mgg1 of HCN. MDI is a diaromatic diisocyanate compound that boils at 208C and is primarily used in the production of rigid foams. Stec and Hull (2011) presented material-LC50 data for rigid polyurethane foam and polyisocyanurate foam, calculated using rat lethality data from ISO 13344 (1996).
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