Chemistry

Organic Polymers, natural or synthetic, are polymerized monomers consisting mainly of  Carbon and Hydrogen, often with other added functional groups/elements like, Halogen, Sulfur, Nitrogen, -C=O, -OH, -COOH, -NH2, -NO2, -SO2,  or –CN. The chemical properties, the thermal stability, the flammability and the products of combustion of these polymers depend on the carbon chain skeleton, structure (aliphatic, alicyclic or aromatic), the addends, and the position the addends occupy in the structure. The Combustion products are often toxic.

Explosives are that group of Chemicals which can react violently at a very high rate with the Oxygen available in situ in the explosophore like NO2 (as cited in Chemistry of some Explosives, p.708). The oxidation can be triggered under suitable condition, like mechanical shock or static electricity. This phenomenon is detonation, releasing lot of thermal energy at a very high rate producing shock waves. The nature of detonation, phenomena and the end products differ from one chemical to another depending on type of carbon chain - aliphatic or aromatic, quantum of the explosophore (NO2) etc. The aromatic explosives like TNT, because of their high Carbon content and less O2 for stoichiometric requirement for oxidation, is less active, and hence safe to handle as compared to Nitroglycerin where the available Oxygen is more than sufficient and hence highly active and unsafe to handle.

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Chemistry of Some Polymeric Materials and Some Explosives
Organic Chemicals exhibit unique properties like polymerization, combustibility, detonatability etc. These properties are gainfully utilized often by the Human Society. How ever there are hazards like Explosion, Toxicity and Pollution in handling and using them.
Toxicity of Burning Tire
Automobile tire being made up of natural or synthetic rubber, poly cis 1,4 isoprene (C5H8)n  or poly cis-l,4-butadiene respectively (as cited in Chemistry of Some Polymeric Materials, p. 695,696), vulcanized with Sulfur, on burning produces a mixture of CO2, CO, and SO2. The concentrations of CO2, CO, and SO2 at the scene of burning of automobile tires are given as 7000 PPM, 1700PPP and 600 PPM respectively. The lethal dosages of these are taken from MSDS data available in the Net, and are tabulated.
 
Table.1Contaminant Concentration vs Lethal Dosage

It can be seen that Carbon monoxide is more dangerous than others and the indicated concentration of 1700PPM is life threatening to FS personals responding to fires. The lethal concentrations of the other two are much higher than the prevailing concentrations.

Combustion products of Burning Polyacrylonitrile
The Poly acrilonitrile is a polymer of Acrilonitrile (Vinyl Cyanide). This is fairy stable
and hence used for the manufacture of Textile fibers. To enhance its safety, fire retardants are

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added during the manufacture of the textile fibers. How ever when it is subjected to burning,
CO2 and CO are the emitted predominantly. Since the polymer contain -CN group, HCN will
also be emitted. Tsuchiya (1977) gives experimental findings showing that the emission of HCN from the burning Poly acrylonitrile increases with rise in burning temperature (p.273, 274,279). He concludes, “In non-oxidizing atmospheres higher temperatures favor greater formation of HCN. In an oxidizing atmosphere HCN increases to a maximum value and decreases with increasing temperature or increasing air supply” (p.280). So burning /smoldering Polyacrylonitrile is hazardous as it produces CO and HCN.

Uniqueness of TNT as a military explosive
Tri Nitro Toluene is a military explosive.  A cursory look at its formula shows high carbon content, being an aromatic compound as against Nitro glycerin. The Oxygen available, after oxidizing the Hydrogen is stoichiometrically not sufficient for complete oxidation of Carbon to Carbon dioxide. Hence this molecule is comparatively stable than the Nitroglycerine, which being aliphatic, has low carbon content and the Oxygen available in the explosophore (NO2) is more than sufficient for complete oxidation of both Carbon and Hydrogen. So Nitro glycerin is very active, sensitive and unstable and hence highly risky. But in the case of TNT, it is fairly stable and hence safe to handle and transport.  More over, TNT being an aromatic chemical it has got higher melting point, 81OC (as cited in Chemistry of some Explosives, p 708) than Nitroglycerine which exists as a liquid at ambient temperature. These properties of TNT come in handy for the use and it’s maneuverability in forming castable explosives and handling them safely by the military persons.