Practical electrical equipment and installations in hazardous areas

1 Introduction ................................................................................................................ 1 1.1 Introduction ................................................................................................. 1 1.2 Approach ..................................................................................................... 4 1.3 Historical development ................................................................................ 5 1.4 Bird’s eye view of legislation and research in other countries ...................... 6 1.5 The certification ........................................................................................... 8 1.6 Conclusion .................................................................................................. 9 2 Electrical energy, ignition and flammability .............................................................. 10 2.1 Electrical energy and ignition ..................................................................... 10 2.2 The basics of electricity ............................................................................. 10 2.3 Electrical heat energy ................................................................................ 19 2.4 Sources of ignition ..................................................................................... 20 2.5 Flammability .............................................................................................. 22 2.6 Flammability principles .............................................................................. 25 3 Area classification .................................................................................................... 27 3.1 General ..................................................................................................... 27 3.2 Principles of safety .................................................................................... 28 3.3 Hazards and hazardous areas ................................................................... 28 3.4 Basic properties of combustible and ignitable material .............................. 30 3.5 Basis of area classification ........................................................................ 32 3.6 Zonal classification .................................................................................... 34 3.7 Plant operations – normal and abnormal ................................................... 35 3.8 Area classification – gas and vapors ......................................................... 36 3.9 Area classification – dust ........................................................................... 53 3.10 Classification procedure ............................................................................ 55 3.11 Responsibility and personnel involved ....................................................... 56 3.12 Documentation .......................................................................................... 57 3.13 Policy and guidelines for implementation ................................................... 58 3.14 Area classification examples ..................................................................... 62 3.15 Summary of area classification .................................................................. 78 3.16 A case study .............................................................................................. 79 4 Design philosophy and selection of equipment/apparatus ........................................ 81 4.1 General ...................................................................................................... 81 4.2 Risks … history ..........................................................................................82 4.3 Classification concepts ..............................................................................84 4.4 Equipment … a definition ...........................................................................85 4.5 Apparatus grouping ................................................................................... 86 4.6 Surface temperature classification .............................................................88 4.7 Concepts and techniques of explosion protection ......................................92 4.8 Methods of explosion protection ................................................................ 93 4.9 Typical applications of methods of protection .............................................97 4.10 Mixed techniques .......................................................................................98 4.11 Dust explosion-protection methods .......................................................... 100 4.12 Selection of explosion-protection technique for safeguarding .................. 102 4.13 Conclusion ............................................................................................... 105 5 Protection concept ‘d’ ............................................................................................. 106 5.1 General .................................................................................................... 106 5.2 Definitions ................................................................................................ 107 5.3 Certification in brief .................................................................................. 109 5.4 Construction requirements ....................................................................... 109 5.5 Flameproof theory .................................................................................... 112 5.6 Other general requirements for explosive atmospheres ........................... 113 5.7 Testing ..................................................................................................... 114 5.8 Grouping and effect of temperature classification .................................... 114 5.9 Conditions of use ..................................................................................... 116 5.10 Illustrations of mechanical construction types ........................................... 118 5.11 Summary ................................................................................................. 123 6 Protection concept ‘e’ ............................................................................................. 124 6.1 General .................................................................................................... 124 6.2 Definitions ................................................................................................ 124 6.3 Principles of design for increased safety .................................................. 125 6.4 Certification (components) ....................................................................... 126 6.5 Construction requirements ....................................................................... 126 6.6 Principles of testing .................................................................................. 130 6.7 Periodic testing and repair of electrical apparatus .................................... 132 6.8 Conditions of use ..................................................................................... 135 6.9 Standards for Ex ‘e’ ................................................................................. 137 7 Protection concept ‘n’ ............................................................................................. 138 7.1 General .................................................................................................... 138 7.2 Definitions ................................................................................................ 138 7.3 Principles of design .................................................................................. 139 7.4 Certification .............................................................................................. 139 7.5 Construction requirements ....................................................................... 139 7.6 Conditions of use ..................................................................................... 142 7.7 Illustrations .............................................................................................. 142 7.8 Standards for Ex ‘n’ ................................................................................. 143 8 Protection concept ‘i’ principles ...............................................................................144 8.1 Origins of intrinsic safety ..........................................................................144 8.2 Principles of IS .........................................................................................145 8.3 Electrical theory to explain IS ...................................................................146 8.4 Implementation of IS .................................................................................153 8.5 The shunt diode safety barrier ..................................................................157 8.6 Associated apparatus ...............................................................................167 8.7 Electrical apparatus in the hazardous area ...............................................169 8.8 Enclosures ...............................................................................................176 8.9 Temperature .............................................................................................177 8.10 The IS systems concept ...........................................................................179 8.11 An IS ‘system’ ...........................................................................................179 8.12 System documentation .............................................................................179 8.13 Assessment of safety ...............................................................................180 8.14 Simple apparatus .....................................................................................181 8.15 Safety parameters ....................................................................................182 8.16 Temperature classification of systems ......................................................182 8.17 Systems concepts in other standards .......................................................182 8.18 Standards for Ex ‘i’ ...................................................................................183 9 Protection concept ‘p’ .............................................................................................184 9.1 General ....................................................................................................184 9.2 Definitions ................................................................................................185 9.3 Development of standards for Ex ‘p’ .........................................................186 9.4 Construction requirements .......................................................................186 9.5 Principles of application ............................................................................189 9.6 Other design requirements .......................................................................192 9.7 Operation of .............................................................................................194 9.8 Testing .....................................................................................................195 9.9 Summary ..................................................................................................196 9.10 Standards of Ex ‘p’ ...................................................................................197 10 Other concepts .......................................................................................................198 10.1 General ....................................................................................................198 10.2 Ex ‘o’: oil filling ..........................................................................................198 10.3 Ex ‘q’: quartz/sand filling ...........................................................................199 10.4 Ex ‘m’: encapsulation ................................................................................200 10.5 Component certification ............................................................................201 10.6 Special type of protection ‘s’ (IEC Concept Code Symbol Ex ‘s’) ..............201 10.7 Multiple certification ..................................................................................203 10.8 Selection of certification method ...............................................................204 10.9 Apparatus for use in dust risks .................................................................204 11 Earthing and bonding .............................................................................................207 11.1 Earthing ....................................................................................................207 11.2 Personnel safety .......................................................................................207 11.3 Hazardous area considerations ................................................................209 11.4 Earthing and bonding ............................................................................... 210 11.5 Static electricity ........................................................................................ 212 11.6 Clean and dirty earthing ........................................................................... 215 11.7 Electrical interference .............................................................................. 216 11.8 Earthing terminology ................................................................................ 218 11.9 Connection of earthing systems ............................................................... 221 11.10 Power supply systems ............................................................................. 223 11.11 Portable equipment using batteries .......................................................... 226 11.12 Earthing arrangement standard solutions ................................................ 226 11.13 Earth loops .............................................................................................. 228 11.14 Computer earthing ................................................................................... 229 11.15 Surge protection systems ........................................................................ 232 11.16 Standards and codes of practice .............................................................. 233 12 Installations ............................................................................................................ 234 12.1 Introduction to installation requirements ................................................... 234 12.2 Installation requirements .......................................................................... 234 12.3 IEC 60079-14: standard contents ............................................................ 235 12.4 Other relevant installation standards and codes ...................................... 236 12.5 Safety documentation .............................................................................. 236 12.6 General requirements of the standard ...................................................... 236 12.7 Practical aspects of IS installations .......................................................... 256 12.8 Other considerations affecting installation ................................................ 268 12.9 Other installation issues ........................................................................... 268 13 Inspection and maintenance .................................................................................. 270 13.1 Inspection and maintenance .................................................................... 270 13.2 Integrity ‘preserved’ ................................................................................. 271 13.3 Scope of IEC 60079-17 ........................................................................... 271 13.4 General requirements .............................................................................. 272 13.5 Inspections .............................................................................................. 273 13.6 The insulation test .................................................................................... 274 13.7 Maintenance ............................................................................................ 275 13.8 Testing ..................................................................................................... 278 13.9 Unauthorized modification ....................................................................... 279 13.10 Earthing integrity verification .................................................................... 279 13.11 BS 5345 inspection requirements ............................................................ 280 14 Safe working practices ........................................................................................... 282 14.1 General .................................................................................................... 282 14.2 Safety observations ................................................................................. 282 14.3 Danger signals of electrical malfunctioning .............................................. 283 14.4 Need for inspection and maintenance ...................................................... 284 14.5 Maintenance and safe practices .............................................................. 294 14.6 Fault-finding – safety ensured .................................................................. 297 14.7 Insulation testing in hazardous area ........................................................ 297 14.8 Earthing in hazardous area ...................................................................... 298 14.9 Handling ‘fall out of fire and electrical shock’ ............................................ 300 15 Fault-finding and testing .........................................................................................302 15.1 Fault-finding .............................................................................................302 15.2 Fault-finding routine ..................................................................................302 15.3 Safety assessment of testing ....................................................................304 15.4 Test equipment .........................................................................................304 15.5 Use of uncertified test apparatus ..............................................................308 15.6 Interface testing ........................................................................................311 15.7 Certified apparatus ...................................................................................314 15.8 IS apparatus repair procedure ..................................................................315 16 ATEX Directive .......................................................................................................318 16.1 General ....................................................................................................318 16.2 Definitions ................................................................................................324 16.3 Scope of the ATEX Directive ....................................................................325 16.4 Bird’s eye view of ATEX Directive .............................................................344 16.5 Summary ..................................................................................................351 Appendix A: IEC series standard titles for explosive atmospheres .....................................352 Appendix B: Listing of IS standards and codes of practice by country ...............................355 Appendix C: IEC 79-17 Ex ‘I’ inspection schedule ............................................................357 Appendix D: CENELEC members .....................................................................................359 Appendix E: IP code ..........................................................................................................360 Appendix F: Standards reference ......................................................................................361 Appendix G: Familiarization with electricity ........................................................................362 Appendix H: ATEX Directive ..............................................................................................372 Appendix I: Properties of combustible compounds ............................................................374 Appendix J: Important changes to AS/NZS 2381.1 ...........................................................377 Appendix K: Practical exercises for hazardous area course ..............................................381