The authors also noted that the presence of aldehydes was detected during the flaming combustion of the flexible foam, albeit in extremely low yields. 1992), shown in Fig. NO. The resulting substituted urea can then react with another isocyanate to pro-duce a biuret linkage (Scheme 4). Polyurethane foams based on polyether polyols will have a lower decomposition temperature in air than polyester polyol based foams. Work by Guo et al. Some fire models, such as the cone calorimeter, fire propagation apparatus and smoke density chamber use the temperature of the radiant heater to preselect the radiant heat flux, and then check this using a radiant heat flux meter. combustion modified high resilience polyurethane foam, Alarie Y (2002) Toxicity of Fire Smoke. To a lesser extent, parameters such as temperature and oxygen concentration also affect the yields of toxic products. This results in relativelyhigh yields of CO and HCN during under-ventilated flaming and relatively low yields during well-ventilated flaming. There are two reasons for this: The yields of the major toxic products (carbon monoxide (CO) and hydrogen cyanide (HCN)from N containing materials) will be much greater. In both rigid and flexible foams, aniline and p-aminotoluene were reported, which correlates with the work of Ravey and Pearce (1997) who reported that isocyanates that did not volatilise were converted into amines in the condensed phase. Terence Richard Hull. The authors tested a rigid polyurethane foam using a NBS cup furnace (as described in Levin et al. 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. The review suggested that the addition of fire retardants did not appear increase the overall combustion toxicity of polyurethane foams. 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. ISO/TS 19700 (2013) Controlled equivalence ratio method for the determination of hazardous components of fire effluents the steady state tube furnace. ISO 13571 (2007) considers the four major hazards from fire which may prevent escape (toxic gases, irritant gases, heat and smoke obscuration). The half-scale ISO 9705 experiments showed a wider range of ventilation conditions up to ~2.0. . Fire Technology 51:p318, Blomqvist P, Lonnermark A (2001) Characterization of the combustion products in large-scale fire tests: comparison of three experimental configurations. The polyisocyanurate, on the other hand, produced slightly more HCN than the rigid foam (17mgg1 vs 12mgg1). Those with constant combustion conditions are more suited to producing data suitable for comparison and modelling: the steady state tube furnace (SSTF) (ISO/TS 19700 2013) has been specifically designed to achieve this. Most rigid foams and speciality polyurethanes use polymeric MDI derivatives which are mixtures components such as dimers and trimers (Fig. International Maritime Organisation, London, Garrido MA, Font R (2015) Pyrolysis and combustion study of flexible polyurethane foam. From this, the library of data was sorted into categories of combustion/pyrolysis conditions, material/product, type of test animal and toxicological endpoint. 50 Aromatic isocyanates are more reactive than aliphatic isocyanates due to the electronic effects of the aromatic ring. Isocyanates are a highly reactive family of compounds that are characterised by the RN=C=O functional group (where R can be any aliphatic or aromatic functionality). A summary of these structures is shown in Fig. 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. Over 90% of all industrial polyurethanes are based on either TDI or MDI (Avar et al. PDF CORE - Aggregating the world's open access research papers 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. 2012). Chem Co., Dow, Hertzberg T, Blomqvist P, Dalene M, Skarping G (2003) Particles and Isocyanates from Fires. Will polyurethane melt under heat? - remodelormove.com The methods of assessment of fire toxicity are outlined in order to understand how the fire toxicity of polyurethane foams may be quantified. The Steady state tube furnace apparatus, ISO/TS 19700. 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. In many studies (such as those by Stec and Hull (2011), Purser and Purser (2008a) and Blomqvist et al. Foams Under Laboratory Conditions, Fire Research Note, No 1039. 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. Comparing the toxic potencies of different materials, the lower the material-LC50 (the smaller the amount of materials necessary to reach the toxic potency) the more toxic the material is. Overall, the report provides access to a large pool of data organised into a material-LC50 and also helps demonstrate that the large majority of data available is for well-ventilated tests. (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. The methods of assessment of fire toxicity are outlined in order to understand how the fire toxicity of polyurethane foams may be quantified. Rigid MDI based foams are primarily used for insulation in the construction industryand can also be found in the transport industry. As polyurethane foams have very low thermal inertia, application of heat or a small flame can be enough to ignite them. FEC model from ISO 13571. 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. 2007). depends on the mass loss rate of the specimen and the available air; for most methods one or both are unknown; will be increased by an unknown factor if products are recirculated into the flame zone. Fire and Materials 31:p327354, Schnipper L, Smith-Hansen ES (1995) Reduced combustion efficiency of chlorinated compounds, resulting in higher yields of carbon monoxide. However, bench-scale methods which allow the combustion conditions to change during the test are much more difficult to relate to full-scale fires, because the duration of each condition is unknown, and the behaviour of fires changes on scale-up. The PIR at 1.75 resulted in 15% of the fuel nitrogen being recovered as HCN. National Bureau of Standards, Gaithersburg MD, Barbrauskas V, Singla V, Lucas D, Rich D (2015) Letter to the Editor- Questions about the conclusions in Blais and Carpenter 2013. Only the SSTF has a heated reaction zone which replicates the hot layer. The authors acknowledged that further investigation of the steady state tube furnace was warranted as in some of the testing they suspected an instrumental error, since they were unable to account for roughly two-thirds of the total carbon from the sample and detected unusually low levels of CO2 during the under-ventilated tests. 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. Thermogravimetric analysis and differential scanning calorimetry (TGA/DSC) showed that the polyether based polyurethane began to decompose at 258C, with a second decomposition stage at 350C (which could be attributed to the fragmentation of the polyether polyol).
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