The basic principles of flameproof enclosure

In the same manner, temperatures exceeding the ignition temperatures (see Table 1.3 in Section 1.2.2) or the maximum surface temperatures according to the temperature class of the apparatus (see Table 4.1 in Chapter 4) are permissible inside of d. This covers windings and rotors in motors, especially for low temperature classes T4, T5 and T6 as well as the discharge tubes of high pressure sodium or mercury vapour lamps in case of a broken lamp bulb, or the ovens of gas chromatographs. 

generally, the ignition of the internal gas-air mixture shall be taken into account. The enclosure itself shall fulfil two main features  

After many years of research in this field, two essential facts have been discovered  

The MESG values of gas-air mixtures depend on the width L of the joint. In IEC 60079-1 A, the MESG values refer to L = 25 mm (and this is the reference value for defining MESG values in general). In trials, L has been varied between 0 (zero ) and 50 mm [2]. The main result obtained has been (Fig. 6.76)  

Even with a zero width of a flameproof joint, there will be no flame transmission if the gap is suitably reduced. 

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Remembering the basic principles of flameproof enclosures, two main characteristics of such enclosures shall be proved by type testing they shall withstand the internal overpressure caused by the ignition of a combustible gas-air mixture inside, and they shall prevent flame transmission to the environmental hazardous atmosphere. So, such a test cycle is divided into three parts ... 

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