Flammability Diagram

Safe dilution requirements can be given for the gas phase in a flammability diagram or equation (270,273). Alternatively, safe vapor dilution can be given in terms of the Hquid storage conditions where allowance can be made for solubility of the inert gas in Hquid ethylene oxide (273). 

FIGURE 3-10. Flammability diagram for methane-oxygen-nitrogen mixtures. (Courtesy of L. G. Britton.)... 

Flammable limits are important as they indicate the range of concentrations within which a comhnstion reaction may occnr. If a concentration of a fnel-oxidant mixtnre can be maintained below the LFL or above the UFL, then there is no possibility of flame propagation. Fignre 3-10 (page 32) is a typical flammability diagram with the flammable zone between the LFL and the UFL indicated. 

Figure 7-47. Flammability diagram for the system gasoline vapor-water vapor-air at 70°F and at 212°F and atmospheric pressure. By permission, U.S. Bureau of Mines, Bulletin 627 [43],...

Figure 6-6 Flammability diagram for methane at an initial temperature and pressure of 25°C and 1 atm. Source C. V. Mashuga and D. A. Crowl, Application of the Flammability Diagram for Evaluation of Fire and Explosion Hazards of Flammable Vapors, Process Safety Progress (1998), 17(3) 176-183.

The shape and size of the flammability zone on a flammability diagram change with a number of parameters, including fuel type, temperature, pressure, and inert species. Thus the flammability limits and the LOC also change with these parameters. 

Appendix C derives several equations that are useful for working with flammability diagrams. These results show that ... 

If two gas mixtures R and S are combined, the resulting mixture composition lies on a line connecting the points R and S on the flammability diagram. The location of the final mixture on the straight line depends on the relative moles in the mixtures combined If mixture S has more moles, the final mixture point will lie closer to point S. This is identical to the lever rule used for phase diagrams. 

If a mixture R is continuously diluted with mixture S, the mixture composition follows along the straight line between points R and S on the flammability diagram. As the dilution continues, the mixture composition moves closer and closer to point S. Eventually, at infinite dilution the mixture composition is at point S. 

The determination of a complete flammability diagram requires several hundred tests using a specific testing apparatus (see Figure 6-14 on page 255). Diagrams with experimental data... 

Figure 6-8 Experimental flammability diagram for methane. (Source C. V. Mashuga, Ph.D. dissertation (Michigan Technological University, 1999).

Draw a flammability diagram for n-butane. The experimentally reported LOC for n-bu-tane is 12%. What must the oxygen concentration be reduced to before pumping in butane What butane concentration must the vapor be reduced to before pumping air into the vessel before taking it out of service ... 

Using the Flammability Diagram To Avoid Flammable Atmospheres... 

If a detailed flammability diagram is lacking, then the ISOC is estimated. One approach is to use the intersection of the LFL with the stoichiometric combustion line. A line is drawn... 

Figure 4.16 Flammability diagram for three-component systems at 26 °C and 1 atm (taken from Zabetakis [5])...

Flammability Diagram Figure 23-4 shows a typical flammability diagram. Point A shows how the scales are oriented—at any point on... 

Crowl (Understanding Explosions, American Institute of Chemical Engineers, New York, 2003, App. A) derived a number of rules for using flammability diagrams ... 

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