Aromatic isocyanates are more reactive than aliphatic isocyanates due to the electronic effects of the aromatic ring. However, when >2.0 the yield of HCN decreased, falling to 10mgg1 at ~2.75. When =1 the theoretical amount of air is available for complete combustion to carbon dioxide (CO2) and water. More recent studies have supported and expanded upon the aforementioned thermal decomposition mechanisms of polyurethane foams. The authors noted that the polyester polyols were more stable than the polyether polyols, with the latter fragmenting at a lower temperature (300400C). In an attempt to improve the understanding of the thermal decomposition of polyurethanes, Rogaume et al. For the purpose of estimating toxicity in fires, fire growth has been classified into a number of stages (ISO 19706 2011): Although on some occasions smouldering (oxidative pyrolysis) can generate toxicologically significant quantities of effluent (for example smouldering cotton, or polyurethane foam), typicallythe rate of reaction, and hence the amount of toxic species generated will be small, so it is unlikely to affect anyone outside the immediate vicinity. 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. The data was presented as material-LC50 values for 30min exposures with 14-day post-exposure of test animals and can be found in Tables10, 11 and 12. Only the SSTF has a heated reaction zone which replicates the hot layer. 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. 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). Animal studies provide most of what we know about the dangerous effects of toxic substances. 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. CO also combines with myoglobin in the muscle cells, impairing diffusion of oxygen to cardiac and skeletal muscles (Purser 2008b). CO yields are generally very low for well-ventilated conditions (in the absence of halogens) but increase considerably under-ventilated combustion conditions. By using infrared analysis, the authors were able to detect a range of compounds at each step, as summarised in Fig. 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. Avar G, Meier WU, Casselmann H, Achten D (2012) Polymer Science: A Comprehensive Reference, Polymer Science: A Comprehensive Reference, 10, p411-441. In others, under reduced oxygen concentrations, the fuel lifts from the surface, but ignition does not occur (Christy et al. Michal (1982) reported a similar trend at a fixed air flow rate. The relation of the FED to the material-LC50 is given in equation4. PML 1998-A97. As the main reactive group that isocyanates react with, polyols are a major component of the resulting polyurethane product. Woolley WD, Wadley AI, Field P (1972) Studies of the thermal decomposition of flexible polyurethane foams in air. (2011) Aerospace series - Burning behaviour of non-metallic materials under the influence of radiating heat and flames - Determination of gas components in the smoke; ABD 0031 Fire-Smoke-Toxicity (FST) Test Specification (Airbus Industries); Boeing BSS 7239, Test method for toxic gas generation by materials on combustion. Toxic product yield data from the smoke density chamber (ISO 56592 2012), the controlled atmosphere cone calorimeter (based on ISO 56601 2002), the fire propagation apparatus (FPA) (ASTM E 2058), the French railway test (NFX) (NF X 70100 2006), and the steady state tube furnace (SSTF) (ISO/TS 19700 2013) were compared to published large-scale enclosure fire data (from a standard ISO 9705 room) for two polymers, polypropylene (PP) and polyamide 6.6 (PA 6.6). Carbodiimides are produced by the reaction of isocyanates in the presence of a catalyst (such as phospholine oxides) (Scheme8) (Avar et al. For example, polyurethane foam, when burned, gives off cyanide gas. (1990) also reported increased HCN yields when the sample was allowed to smoulder before flaming in similar apparatus as above. This equation only relates to lethality, or cause of death. 1 Fire Safety Journal 7:p11, Kavanagh BP, Pearl RG (1995) Inhaled nitric oxide in anesthesia and critical care medicine. Toxic product yields frommaterials involved in fires depend on a number of factors. Similarly, Busker et al. Tests were carried out on the CMHR-PUF at 650C and 850C and at 700C for the PIR in order to achieve steady flaming conditions. 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. For any larger fire there will always be a significant yield of CO, HCN (from nitrogen containing materials), hydrocarbons and smoke. Toxicology 47:165170, Kaplan HL, Grand AF, Hartzell GE (1984a) Toxicity and the smoke problem. However, once one of the groups forms a urethane or urea, the activating effect on the other isocyanate is reduced, as ureas and urethanes are weaker activating groups than isocyanates. Paabo and Levin (1987) reviewed the literature of the toxic product generated by the combustion of rigid polyurethane foams. The cone calorimeter (ISO 56601 2002) is probably the most widely used apparatus for measurement of flammability properties such as ignitability and heat release rate (Schartel & Hull 2007). The chemical additives to the polyurethane are said to give off a distinct chemical odor that lessens after adequate ventilation. The authors noted that a large number of the data available relating to the test conditions were vague or completely undefined. 1986). Other common diisocynates include hexamethylene diisocyanate (HDI), 1,5-naphthalene diisocyanate (NDI) and isophorone diisocyanate (IPDI) (Fig. The two main families of polyols used are polyether polyols and polyester polyols (Fig. The half-scale ISO 9705 experiments showed a wider range of ventilation conditions up to ~2.0. 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. This is due to the large range of available fire retardants found in polyurethane foams, which suggests that the toxicity will likely follow the general trends in the literature for all materials regarding fire retardants. 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. It gives off toxic gasses and smoke, which makes it difficult to evacuate and put out a fire. 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. Woolley WD, Fardell PJ, Buckland IG (1975) The Thermal Decomposition Products of Rigid Polyurethane. Equation In contrast to the relativelywell-defined effects of asphyxiants, the effects of exposure to irritants are more complex. 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. 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). Damage was most severe to the exterior. The difference in the decomposition of rigid and flexible polyurethane foams was investigated by Chun et al. 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. Fire Safety Journal 40:439465, Aneja A (2002) Chapter 2, Structureproperty Relationships of Flexible Polyurethane Foams, PhD. combustion modified high resilience polyurethane foam, Alarie Y (2002) Toxicity of Fire Smoke. Others, such as the NF X 70100, and the ISO/TS 19700 SSTF use the furnace temperature setting to ensure a consistent radiant heat flux. Over 90% of all industrial polyurethanes are based on either TDI or MDI (Avar et al. At 300C, free isocyanates and alcohols were produced from the decomposition of these biscarbamates. The strain of two electronegative atoms (N and O) results in electron density being pulled away from the carbon atom, giving it a strong partial positive charge. Known as "solid gasoline" in the insurance industry, once a polyurethane fire starts, it usually results in a total loss of property and loss of life, according to Federated Insurance. However, instead of finding my answer I found seemingly endless reports on websites claiming that memory foam gives off potentially toxic fumes. 9). In China and Japan, there are specific restrictions on the use of materials with high fire toxicity in high risk applications such as tall buildings, while an increasing number of jurisdictions permit the alternative performance based design approaches to fire safety. California Privacy Statement, This slight decrease is probably within the limits of experimental error, as it does not follow the general trend shown by most materials. Polymer Degradation and Stability 98:535541, Anderson RA, Watson AA, Harland WA (1981) Fire Deaths in the Glasgow Area: I General Considerations and Pathology. Although the authors intended for the bench scale test methods and the large scale test to represent post-flashover room fires, the tests resulted in CO and HCN yields that suggested the combustion conditions were not under-ventilated (Table7). The Model 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. Based on this data, the HCN recovery fraction was calculated for both materials. Further decomposition occurred about 600C with the fragmentation of the yellow smoke, primarily into hydrogen cyanide and small quantities of acetonitrile, acrylonitrile and benzonitrile. 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. Anyone you share the following link with will be able to read this content: Sorry, a shareable link is not currently available for this article. Using the methodology in ISO 13344, the authors also calculated the fractional effective dose (FED) of the individual toxicants sampled. The NFX generates data intermediate between the well-ventilated and under-ventilated fire conditions. 2 The polyisocyanurate, on the other hand, produced slightly more HCN than the rigid foam (17mgg1 vs 12mgg1). 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. Its widespread availability has encouraged its adaptation to toxic gas generation and assessment. 3) (Aneja 2002). Based on the temperature of the test, the yields of HCN are extremely low when compared with the CO yields. (2007) suggests that their yields are not heavily dependent on the ventilation conditions and that the yields would likely only increase by a small amount during under-ventilated flaming. 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. 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). The authors tested a rigid polyurethane foam using a NBS cup furnace (as described in Levin et al. The smoke density chamber (ISO 5659-2) showing a sampling probe for fire smoke toxicity. 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). 3 These reactions are accelerated in the presence of oxygen, which reduces the temperature of the decomposition steps. The fire toxicity of polyurethane foams.
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