Page 10 - Electrical Installation in Hazardous Area

Contents vii

4.4.2 Liquid releases below boiling point 120
4.4.3 Liquid releases above boiling point 120
4.5 Releases in areas which are not well ventilated 121
4.5.1 Example of gas release using BS/EN 10079-10
formulae 123
4.6 Conclusion 123

5 Area classification practice for gases, vapours and mists in
areas which are not freely ventilated 125
5.1 Typical areas of restricted ventilation 126
5.1.1 Open areas surrounded by walls 126
5.1.2 Covered areas (dutch-barn type) 126
5.1.3 Above-ground rooms 126
5.1.4 Below-ground rooms 127
5.2 Effect of walls on hazardous areas 127
5.3 Roofs without walls or associated with one, two or
three walls 130
5.3.1 Roofs without walls 130
5.3.2 Roofs associated with one wall 132
5.3.2 Roofs associated with two walls 132
5.3.4 Roofs associated with three walls 133
5.4 Rooms above ground 134
5.4.1 The application of additional general
ventilation 135
5.4.2 The application of additional local ventilation 140
5.4.3 High integrity ventilation 143
5.5 Rooms below ground 144
5.6 Rooms without any internal release but which abut
external hazardous areas 145
5.7 Particular circumstances 146
5.7.1 The paint spray booth 146
5.7.2 The paint drying oven 146

6 Area classification practice for dusts 149

6.1 Properties of dusts 150
6.1.1 The ignition of dust clouds 151
6.1.2 The ignition of dust layers 154
6.1.3 Production of flammable gases and vapours
by dusts 154
6.1.4 Other important dust properties 155
6.2 Area classification for dust releases 155
6.2.1 Sources of dust release 155
6.2.2 Definition of Zones 156
6.2.3 Extents of hazardous areas 158