Page 167 - Electrical Installation in Hazardous Area

Area classification in areas which are not freely ventilated 133

Wall Ground

Source o!
release

Roof
E = Extent of hazardous area taking account of wall
proximity but in absence of roof
V = Height of source of release
X = Distance source/wall
a = E -- Y (with a minimum of 0.5 m over roof)
b = 2y - 2a
Note: Where b is less than E hazardous area
extends behind and over roof to F

Fig. 5.8 Effects of roof over single wall

the roof and down to the ground (see Fig. 5.9). As for one wall, the extents
of hazardous area above the roof line will be determined using Fig. 5.3
and 5.4.

5.3.4 Roofs associated with three walls

Where three walls exist, the situation is entirely different and the area
should be treated as a room as described later in this chapter, giving a
hazardous area as described in Fig. 5.10, which is based on Table 3.2 in
the same way as would be the case for an opening, such as a door in
a room.