Page 9 - Electrical Installation in Hazardous Area

vi Contents

3 Area classification practice for gases, vapours and mists in
freely ventilated situations 43
Introduction 43
3.1 Containment of flammable materials 44
3.1.1 Effects of storage conditions 44
3.1.2 Effect of sunlight on storage vessels 45
3.1.3 Oxygen enrichment 45
3.1.4 General consideration of release 46
3.2 Generalized method of area classification 46
3.2.1 Generalized zonal classification specification 46
3.2.2 Generalized extents of zones 47
3.3 The source of hazard method of area classification 48
3.3.1 Types of release 50
3.3.2 Releases from pipe joints 52
3.3.3 Typical extents of Zone 2 from pipe joint
releases 54
3.3.4 Special pipe joint circumstances 65
3.3.5 Releases from moving seals 65
3.4 Other practical well-ventilated situations 67
3.4.1 The fixed roof vented stock tank 67
3.4.2 The floating roof tank 69
3.4.3 Tanks containing gas, vapour or liquefied
vapours 71
3.4.4 Road and rail tanks for flammable liquids 72
3.4.5 Oil/water separators 76
3.4.6 Other open vessels 78
3.4.7 Open drains 78
3.4.8 Trenches 80
3.4.9 Sampling points 80
3.4.10 Walls and apertures 85
3.4.11 Vents 85

4 Calculation of release rates and the extents of
hazardous areas 87
4.1 Releases of gas and vapour 88
4.1.1 Examples of gas and vapour release 105
4.2 Release of liquid below its atmospheric boiling point 107
4.2.1 Example of liquid release below its
atmospheric boiling point 113
4.3 Release of liquid above its atmospheric boiling point 116
4.3.1 Example of liquid release above its
atmospheric boiling point 118
4.4 Summary of use of equations 119
4.4.1 Gas and vapour releases 119