Flammability region

Simon, D.M., Belles, F.E., and Spakowski, A.E., Investigation and interpretation of the flammability region for some lean hydrocarbon-air mixtures, Proc. Comb. Inst., 4 126,1953. 

Ju, Y, Guo, H., Maruta, K., and Niioka, T., Flame bifurcations and flammable regions of radiative counterflow premixed flames with general Lewis numbers. Combust. Flame, 113, 603, 1998. 

The combustion of butane is preventable by adding nitrogen, carbon dioxide, or even water vapor until the oxygen concentration is below 12.4%. The addition of water, however, is not recommended because any condition that condenses water would move the oxygen concentration back into the flammable region. 

Explosive nature of chemical substances is described with upper and lower explosion limits. The explosiveness of vapour cloud depends especially on the lower explosion limit (LEL). The LEL is the concentration of vapour, at which the vapour cloud is possible to ignite. The wider range between explosion limits means, that it is more probable that the formed vapour cloud is in the flammable region, i.e. the higher tendency for explosion. Edwards and Lawrence (1993) have used explosive limits to determine the explosiveness of chemical substances. 

In all cases steam is present as the main ballast. The role of steam is to decrease the concentration of isobutane and oxygen in the recycle loop and thus keep the reactant mixture outside the flammability region. Water can be easily separated from the other components of the effluent stream, and also plays a positive role in the catalytic performance of POMs. It is also possible that the presence of water favors the surface reconstruction of the Keggin stmcture, which decomposes during the reaction at high temperature, and also promotes desorption of methacrylic acid, saving it from unselective consecutive reactions. 

Practice indicates that the vapors emanating from these vents are rarely within the flammable region, as the nominal atmospheric pressure of the drainage system is not adequate to allow vapor or gas to pass through the 3-4 in (7.5-10 cm) deep catch basin water seals. 

Figure 1.5 Triangular diagram of CFCs based on methane, showing toxic and flammable regions, as well as their commercial names and their normal boiling points in...

Hydrocarbon concentration Below flammability limit Flammable region possible... 

By controlling the oxygen flux, the local reactants composition can be kept outside the flammability region, so that the risk of explosion is eliminated, and hot spots can be avoided. 

Operating at temperatures below the flashpoint of a liquid will avoid the formation of a flammable atmosphere as the vapour concentration will be below the lower flammable limit. It is also possible to work at temperatures where vapour concentrations exceed the upper flammable limit, but in this case it is necessary to pass through the flammable region when the plant is started up and shut down. Additional measures such as inert gas blanketing may be neees-sary at these times. When safety is based on temperature control a margin of at least 5°C should be allowed between the maximum operating temperature and the flashpoint of the liquid. 

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