Restricted breathing enclosure

Figure 2.5 The zone 2 concept according to VDE 0165/1991-02. Requirements for electrical apparatus with arcs or sparks in normal operation and/or temperatures exceeding a defined limit/temperature class. Two types of protection are defined here the schwadensicheres Gehause , comparable with a restricted breathing enclosure , and simple pressurization .

For electrical apparatus outside of this scope, e.g. switchgear, IEC 60079-15 defines a protection technique restricted breathing enclosure. ... 

The advantage of pressurization - compared with other protection techniques, e.g. restricted breathing enclosure - is given by a positive pressure differential permanently maintained in the apparatus interior. Load cycles of the p-apparatus do not affect this pressure differential, and by this way, a cooling-down period caused by reduced or no-load conditions cannot cause an inverted pressure differential (the pressure of the surrounding atmosphere is somewhat higher compared with that in the apparatus interior) which may force the backstream of environmental flammable atmosphere into the interior of an apparatus. Pressurization guarantees safe operational conditions completely independent of load cycles. 

Confined space Ii3> > Metal enclosure Wetness Restricted entry Heavier than air gas Welder inside or on workpiece Carefully evaluvate adequacy of ventillation especially where electrode requires special ventillation or where gas may displace breathing air. If basic electric shock precautions cannot be follwed to insulate welder from work and electrode, use semiautomatic, constant-voltage equipment with cold electrode or stick welder with voltage reducing device. Provide welder helper and method of welder retrieval from outside enclosure. 

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