Page 199 - Electrical Installation in Hazardous Area

Area classification practice for dusts 163

6.3.3 Loading hoppers outside buildings
Where hoppers are in well-ventilated areas (outdoors) the Zones 20 and
21 are as described in Section 6.3.2. The Zone 22 however is different. (See
Fig. 6.3.)

Zone 22
The outdoor situation is one in which there is assumed to be significant air
movement and this will limit the deposition of dust so that the Zone 22
will have a finite size. Because of the air movement, spillage will be blown
away rapidly and housekeeping will cover the unusual situation where it
is not. The size of the Zone 22 in these circumstances is unlikely to exceed
3 m in dimension.
Care should be taken, however, to identify any places where obstructions,
such as walls, could cause build-up of wind-borne dust to allow layers of
dangerous thickness.

References

1 The Factories Act 1961.
2 BS 6467 Electrical Apparatus With Protection by Enclosure for
Use in the Presence of Combustible Dust. Part 2 (1988).
Guide to Selection, Installation and Maintenance.
3 IEC 1241-3 Electrical Apparatus for Use in the Presence of
Combustible Dust. Part 3. Classification of Areas
Where Combustible Dusts are or may be Present.
(Draft 1994) (BS 94/213454 DC)
4 IEC 1241-2 Electrical Apparatus for Use in the Presence of
Combustible Dust. Part 2, Test Methods: Section 1
(1994). Method for the Determination of the Minimum
Ignition Temperature of Dust; Section 2 (1993).
Method for the Determination of the Ignition
Temperature of Dust in Layers; Section 3 (1993).
Method for Determination of Minimum Ignition
Energy for Dust/Air Mixtures.