Explosion protected apparatus temperature classification

Table 3.2(a) VDE 0170/0171/1969-01 Classification of explosion protected electrical apparatus according to the ignition temperature of combustible gas-air or vapour-air mixtures. Maximum surface temperatures of such apparatus... 

Apparatus grouping and temperature classification are described in Chapter 4, especially in Table 4.1 Part A and Table 4.2 Part A for EN and IEC specifications. As a general rule, the ambient temperature (in service) for explosion protected electrical apparatus is limited to the range from 20°C to +40°C. Deviating ambient temperature ranges shall be indicated, e.g. -30°C = Tamb =s +60°C, or the apparatus shall be marked with the symbol X, which indicates special conditions in general. 

Classification and marking of intrinsically safe apparatus concerning explosion groups (I, IIA, IIB, IIC) and temperature classes (T1-T6) are organized in the same way as for, e.g., flameproof enclosure - d (see Tables 4.1 and 4.2, Chapter 4, and Chapter 5 for marking). Some special features, however, which are of importance for type of protection intrinsic safety - i only, will be explained in the following. 

Fusible Link a mechanical release device actiwited by the heat effects of a fire. It usually consist of two pieces of metal joined by a low melting solder. Fusible links are manufactured as various incremental temperature ratings and are subjected to varying normal maximum tension. When installed and the fixed temperature is reached, the solder melts and the two metal parts separate, initiating the desired actions Hazard Analysis the systematic identification of chemical or physical characteristics and/ or processing conditions and/or operating conditions that could lead to undesired events Hazardous Area, Electrical a US classification for an area in which explosive gas/air mixtures are, or may be expected to be, present in quantities such as to require special precautions for the construction and use of electrical apparatus HAZOP an acronym for Hazard and Operability study, which is a qualitative process risk analysis tool used to identify hazards and evaluate if suitable protective arrangements are in place if the process were not to perform as intended and unexpected consequences were to result... 

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