Dust, combustible ignition energy

From a safety standpoint, priority must be given to the measures in item 1. Group 2 cannot be used as a sole protective measure for flammable gas or solvent vapors in industrial practice with sufficient reliability, but can be applied as the sole protective measure when only combustible dusts are present if the minimum ignition energy of the dusts is high (>10 mj) and the operating areas concerned can easily be monitored. 

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... 

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. 

The limits of flammability of dusts have been investigated (30G, 34G, 35G). Using various metal powders, Boyle and Llewellyn (15G) have found the minimum ignition energy to be proportional to particle size. Browning, Tyler, and Krall (10) report a variation of the lean limit as a function of particle size particles of about 60-micron diameter give the leanest combustible mixtures. 

Most organic solids, metals, and some combustible inorganic salts can form explosive dust clouds. In order to have a dust explosion, certain elements are necessary (1) Particles of dust of suitable size, (2) A sufficient source of ignition energy, (3) A concentration of dust within explosive limits. If an explosive dust in air that meets the above criteria occurs in a process, an explosion should be considered inevitable. The process designer of inherently safer plants must take into account the possibility of dust explosions and design accordingly. 

Table 1.8 Minimum ignition energy (high voltage capacitor discharge) for combustible dust-air mixtures, T = +20°C ( = + 68°F), p = 1.013 105Pa...

Ed. 1 Section 3 Method of determining the minimum ignition energy of dust-air mixtures Electrical apparatus for use in the presence of combustible dust... 

TABLE 7.4.3 Influence of tlie Type of Ignition Source and of tlie Ignition Energy on tlie Explosion Data of Combustible Dusts (1-m ... 

In this chapter, the basics of combustion are outlined followed by the fundamentals specific to dust explosions. The measurement and application of dust explosion characteristics, such as ignition temperature, range of flammable concentrations minimum ignition energy are covered. Finally the available methods for control of dust explosion hazard are discussed. 

Rapid release of energy dirough die ignition of atmospheric mixtures of flanuiiable gases, vapors or combustible dusts widiiii the explosive range... 

The MIE of gas — air or vapour—air mixtures can be determined from the structural formula and the molar heat of combustion of the compounds studied, and equations for the calculation are presented. The method is stated to give more accurate results than conventional methods used to assess flammability of mixtures of gas or vapour with air [1], It is claimed that in oxygen MIEs are about a hundredfold lower than in air [2], A study of the ignition behaviour of dusts, including correlation of electrical and mechanical minimum ignition spark energies and ignition temperature is made [3],... 

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