Ignition Energy MIE

The vapor pressure (VP) can be used in conjunction with a measured LEE to estimate flash point. When this is done it is usually found that the calculated flash point is less than the measured value owing to limitations in the flash point test technique (5-1.1.1). Conversely, the LEE can be estimated only approximately from the flash point. The VP can also be used to replace the 10 

FIQURE 5-1.4b. Effect of pressure on MIE of propane in uarious oxygen-nitrogen mixtures. 

TABLE 5-1.4.1 Approximate Vapor-Liquid Equilibrium Temperatures for LFL, LMIE, and UFL Vapor Concentrations at Atmospheric Pressure 

Note Section A-5-6.3 of the 1996 edition of NFPA30 (reiterated in NFPA385) contains erroneous information about switch loading. 

When a tank is emptied of Class I liquid, there is left a mixture of vapor and air, which can be, and often is, within the flammable range. When such a tank is refilled with a Class I liquid, any charge that reaches the tank shell will be bled off by the required bond wire. Also, there will be no flammable mixture at the surface of the rising oil level because the Class I liquid produces at its surface a mixture too rich to be ignitable. 

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Minimum Ignition Energy (MIE) Initiation of flame propagation in a combustible mixture requires an ignition source of adequate energy and duration to overcome heat losses to the cooler surrounding material. Dust and vapor... 

If it is assumed that explosible dust will be present above the MEC, and equipment design data are not required, explosibility testing forP g, and Kg usually has no direct application. However, minimum ignition energy (MIE) testing should be considered to help determine the likelihood of ignition. Since MIE is extremely sensitive to particle size it is especially important to test a sample that is sufficiently fine to represent the worst credible case. 

FIGURE 4-5. The relationship between minimum ignition energy (MIE) and quenching distance... 

Types of dust Ignition temp, of dust cloud, °C Ignition temp, of dust layer, °C Min. ignition energy (MIE), J Min. explosion cone., g/nC... 

The minimum ignition energy (MIE) is the minimum energy input required to initiate combustion. All flammable materials (including dusts) have MIEs. The MIE depends on the specific chemical or mixture, the concentration, pressure, and temperature. A few MIEs are given in Table 6-4. 

TABLE 23-4 Minimum Ignition Energy (MIE) for Selected Gases... 

Minimum ignition energy (MIE) Lowest electrical energy stored in a capacitor which, upon discharge, is just sufficient to effect ignition of the most ignitable atmosphere under specified test conditions. 

See also ADHESIVE LABELS, IGNITION SOURCES, MINIMUM IGNITION ENERGY (MIE)... 

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