Upper flammable limit

Flammability limits. A flammable gas will bum in air only over a limited range of composition. Below a certain concentration of the flammable gas, the lower flammability limit, the mixture is too lean to burn, i.e., lacks fuel. Above a certain concentration, the upper flammability limit, it is too rich to burn, i.e., lacks oxygen. Concentrations between these limits constitute the flammable range. 

Ester Auto-ign ition temp, °c Upper flammable limit, vol % in air Lower flammable limit, vol % in air Healt h Flamma -bihty Reacti -vity Specie s Oral 50 g/kg pel" ppm pel" mg/ m. 

Flash points, lower and upper flammability limits, and autoignition temperatures are the three properties used to indicate safe operating limits of temperature when processing organic materials. Prediction methods are somewhat erratic, but, together with comparisons with reliable experimental values for families or similar compounds, they are valuable in setting a conservative value for each of the properties. The DIPPR compilation includes evaluated values for over 1000 common organics. Detailed examples of most of the methods discussed are available in Danner and Daubert."... 

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. 

For apphcation of Eq. (26-48), x should not exceed 300 m (984 ft). The reason for selec ting 100 percent, instead of the upper flammable limit (UFL), in the equation for Vj is that in an incipient explosion vapor above the UFL may be mixed with additional air and, thereby, contribute to explosion pressure. 

Upper Flammable Limit (UFL) The highest concentration of a vapor or gas (the highest percentage of the substance in air) that will produce a flash of fire when an ignition source (heat, arc, or flame) is present. See also Lower Flammable Limit. At concentrations higher then the UFL, the mixture is too rich to burn. 

Note 1. When loading volatile products such as gasoline, whose vapor concentration can be shown to rapidly exceed the upper flammable limit during tank filling, the velocity-diameter product may be increased to 0.50 mVs- This is consistent with API RP2003 [3]. Similarly, shorter wait periods of 1-2 min can be used. 

Flammable Limits in Air - This is a concentration expressed as percent by volume of the chemical in air, whereby spontaneous combustion will be supported. The lowest concentration where combustion will be supported is known as the lower flammability limit (LFL) or lower explosion limit (LEL). LEL and LFL are considered interchangeable. The upper concentration limit is the UFL (Upper Flammability Limit) or UEL (Upper Explosion Limit). 

Upper Explosive Limit (UEL) or Upper Flammable Limit (UFL) ... 

Important flammability characteristics are the lower and upper flammability limits, the flash point, the minimum ignition energy, the minimum oxygen concentration, and the autoignition temperature. Values of some of these properties are published for many compounds (NFPA, 1994). These numbers have typically been developed under standardized test conditions. Process conditions may influence their values. 

When zinc was added to a tank, the extract fans were operated at full rate with the vent closed. No air could be sucked in, and the concentration of hydrogen rose rapidly above the upper flammable limit (75%). 

Flammable Limits The minimum and maximum concentration of fuel vapor or gas in a fuel vapor or gas/gaseous oxidant mixture (usually expressed in percent hy volume) defining the concentration range (flammable or explosive range) over which propagation of flame will occur on contact with an ignition source. See also Lower Flammable Limit and Upper Flammable Limit. 

Flammable Range The range of concentrations between the lower and upper flammability limits. 

Gas Enrichment The addition of another flammable gas to a gas-air mixture to raise the concentration above the upper flammable limit. 

Upper Flammable Limit (UFL) That concentration of a combustible material in air above which ignition will not occur. It is often, interchangeably, called Upper Explosive Limit (UEL). Mixtures above this limit are said to be too rich. ... 

Figure 7-49B. Variation of upper flammable limits with temperature and pressure. Reprinted by permission from Fire Protection Handbook, 17th Ed. (1991), National Fire Protection Association, Quincy, MA 02269 [34].

Tl = equilibrium temperature at which the lower flammable limit composition exists over liquid in dry air at one atmosphere (theoretical flash point), °C or °F Ty = equilibrium temperature at which the upper flammable limit composition exists over liquid in dry air at one atmosphere, °C or °F... 

The most flammable mixture is usually the stoichiometric mixture for combustion. It is often found that the concentrations of the lower and upper flammability limits are approximately one-half and twice that of the stoichiometric mixture, respectively2,3. 

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