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ID: 578675 • Letter: I
Question
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FSET-3103-Principles of Fire Behaviorl Homework-Assignment-2-(Lecture 3)1 (Due-Tonightfl Question Carbon-containing-materials, can, release, appreciable quantities of carbon-monoxide (CO)m fires. . Likewise materials that contain significant amounts ofnitrogencan generate hydrogen cyanide(HCN) and nitric oxide(NO) Materials with chlorine or fluorine in their molecules can generate hydrogen chloride (HCD and hydrogen fluoride (HF). Finally, some products generate large amounts of soot, which affects the visibility. Indicate in the following table (by marking theappropriate cellswith an X)which toxic gas species are likely to be generated-for the sixtypes of polymeric materials that are listed. Also-indicate-whether you expect the combustion productsto contain large amounts of soot. Tip: read the supplement material!T ·Answer Materiala PPo PVCo PSo PTFEo Nylono WoodoExplanation / Answer
PP is a purely hydrocarbon polymer consisting of propylene monomer units. This species has a very high carbon and hydrogen content but is devoid of any other elements. Thus it is very likely to generate CO and due to a 1:2 ratio of carbon to hydrogen, the excess hydrogen can produce water as vapour which dampens the effective combustion of carbon. Moreover, this will result in generation of copious amounts of soot as the carbon with insufficient temperature and oxygen will undergo partial combustion to give soot which is just amorphous carbon.
PVC contains C, H and Cl. Thus, HCl, CO and some amounts of water vapour are expected. Again due to the high carbon content of this polymer, it is likely to generate a certain amount of soot which is observed as the charred remains after a fire still pungent with HCl smell.
PS contains styrene monomers which have a benzene ring in it. The aromatic ring's presence combined with a high hydrogen content results in oxygen deprivation in the polymer leading to incomplete combustion of the aromatic ring (which itself requires an extraordinary amount of heat to combust due to the high stability) giving large amounts of soot. Of course the carbon which does combust in excess oxygen will generate CO and water vapour.
PTFE as the name suggests contains C and F with no hydrogen. So this polymer is likely to generate extraordinary amounts of HF apart from CO. Owing to the absence of any oxygen depriving combustion products, PTFE will not generate high soot quantity.
Nylon is polymer of caprolactam-derived monomers - amides. So they will contain C, H, N and O. This will give CO, NO, HCN and water vapour. Again due to the evolution of water vapour which is a very good oxygen depriver for a inflaming material and CO with NO which can generate carbon dioxide that easily cuts off oxygen supply, incomplete combustion will result giving high quantities of soot.
Wood is not composed of simple polymers like the ones given before. It is composed of specialized cells sclerenchyma which exist solely to provide structural robustness to the plant material. Therefore wood is likely to contain C, H, N, O, P and S apart from a certain amounts of Cl and depending upon the plant variety F too. Top of all, the plants also sequester large amounts of water inside the wood (unless of course it is completely dry like firewood) and so the combustion products generated by burning wood will be CO, CO2, water vapour, NO, HCN, SO2, trace amounts of HCl, rarely HF and not to mention a large amount of incompletely burnt carbon as soot.