MESG Maximum Experimental Safe

Figure 6.77 MESG (maximum experimental safe gap) values of gas-air mixtures versus power density cr (according to Table 6.26).

Sintered metals show a strong correlation between open porosity and effective gap. (The effective gap weS of a flameproof component is the highest MESG (Maximum Experimental Safe Gap) value of combustible gas mixtures (see Section 1.2.2), for which that component ensures flameproofness. For gas mixtures with MESG < wen, flame transmission occurs.) (see [19]). 

Phillips, H. 1987. A Comparison of Standard Methods for the Determination of Maximum Experimental Safe Gap (MESG). Proc. International Symposium on the Explosion Hazard Classification of Vapors, Gases, and Dusts, pp. 83-108. Publication NMAB-447. National Materials Advisory Board, Washington, DC. 

The upper hemisphere can be adjusted by a fine-pitch thread to defined values w for the gap. The exterior volume V equals nearly 2.5 litres. In both volumes, a and V, the same gas-air mixture normally with T = +20°C and a total pressure of 1.0 105Pa is present. After ignition in a, an MESG value (maximum experimental safe gap) can be found by varying w, so that the flame cannot pass from a to V. These MESG values (ensuring the nontransmission of the flame) show a parabolic function versus the gas concentration c (Fig. 1.3). 

Figure 1.3 Dependence of the maximum experimental safe gap (MESG) on the gas concentration c in air.

Table 2.11 Maximum experimental safe gaps (MESGs) for selected flammable materials (from [7])...

The maximum gap of a combustible substance/air mixture is the gap width at which an ignition through the gap does not occur just any more. The lowest value of all maximum gaps of a substance that was determined under atmospheric pressure in dependence on the substance concentration is the Afaximum Experimental Safe Gap (MESG). The appertaining combustible substance mixture is designated as the most readily ignitable mixture. The gap width depends on the temperature and the pressure. A rise in pressure and temperature leads to a reduction of the gap width. 

---