Flammability limits pressure effect

Volatile Solids, NFPA 325, Quincy, Mass.). Pressure particularly affects flash point and the uppei flammable limit (UFL) see later section entitled Effect of Temperature, Pressure, and Owgen. Mists of high-flash-point liquids may be flammable the lowei flammable limit (LFL) of fine mists and accompanying vapor is about 48 g/m of air, basis 0°C and 1 atm (0.048 oz/fP). 

Effect of Temperature Pressure and Oxygen LFLs and LOCs at 1 atm decrease about 8 percent of their values at near normal room temperature for each 100°C increase. Upper flammable limits increase approximately 8 percent for the same conditions. 

FIGURE 3-9. Effect of various gases on the flammability limits of methane-inert-gas-air mixtures at 25°C (77°F) and atmospheric pressure (Zabetakis 1965). 

Extreme care must be exercised in designing potentially flammable systems to use reliable flammability limits data and to recognize the effects of pressure/temperature on the data and its implications to the safety of the system in question. Unless otherwise indicated, most published data is at atmospheric pressure and ambient temperature and should be corrected for other conditions. 

The temperature and pressure of a liquid system are important in determining the effects created that result in a fire and explosion hazard. Because this relates to the flash point and flammability limits, see Tables 7-21, 7-22 and Figures 7-48, and 7-49A, and 7-49B [34]. 

Mixtures of the tetraoxide with dichloromethane, chloroform, carbon tetrachloride, 1,2-dichloroethane, trichloroethylene and tetrachloroethylene are explosive when subjected to shock of 25 g TNT equivalent or less [1], Mixtures with trichloroethylene react violently on heating to 150°C [2], Partially fluorinated chloroalkanes were more stable to shock. Theoretical aspects are discussed in the later reference [2,3], The effect of pressure on flammability limits has been studied [4],... 

Flammability Limit Dependence on Pressure Pressure has little effect on the LFL except at very low pressures (<50 mmHg absolute) where flames do not propagate. 

FIGURE 4.25 Effect of pressure increase above atmospheric pressure on flammability limits of natural gas-air mixtures (from Lewis and von Elbe [5]). 

Table 10. Effect of Increase in Pressure on Raising the Upper Flammability Limit...

Effect of pressure. Flammability is affected by initial pressure. Normal variations in atmospheric pressure do not have any appreciable effect on flammability limits. 

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