AS 1768-1991

1 - AS/NZS 1768-1991 LIGHTNING PROTECTION
4 - PREFACE
5 - CONTENTS
7 - SECTION 1 SCOPE AND GENERAL
7 - 1.1 SCOPE
7 - 1.2 APPLICATION
7 - 1.3 REFERENCED DOCUMENTS
7 - 1.4 DEFINITIONS
7 - 1.4.1 Air termination
7 - 1.4.2 Air termination network
7 - 1.4.3 Base conductors (base tapes)
7 - 1.4.4 Bond (bonding conductor)
7 - 1.4.5 Downconductor
7 - 1.4.6 Earth impedance (Z)
7 - 1.4.7 Earth potential rise (EPR)
7 - 1.4.8 Earthing boss (terminal lug)
7 - 1.4.9 Earthing conductor
8 - 1.4.10 Earthing electrodes (earth rods or ground rods)
8 - 1.4.11 Earthing resistance
8 - 1.4.12 Earth termination (earth termination network)
8 - 1.4.13 Explosive gas atmosphere
8 - 1.4.14 Finial
8 - 1.4.15 Hazardous area
8 - 1.4.16 Joint
8 - 1.4.17 Lightning flash (lightning discharge)
8 - 1.4.18 Lightning flash density
8 - 1.4.19 Lightning protection system
8 - 1.4.20 Lightning strike
8 - 1.4.21 Lightning strike attachment point
8 - 1.4.22 Lightning stroke
8 - 1.4.23 Side flash
8 - 1.4.24 Striking distance (ds)
8 - 1.4.25 Structure or object
8 - 1.4.26 Surge arrestor
8 - 1.4.27 Test link
8 - 1.4.28 Thunderday
8 - 1.4.29 Zone of protection
9 - SECTION 2 ANALYSIS OF NEED FOR PROTECTION
9 - 2.1 NEED FOR PERSONAL PROTECTION
9 - 2.2 NEED FOR PROTECTION OF BUILDINGS AND CONTENTS
9 - 2.2.1 Factors governing decision whether or not to protect
9 - 2.2.2 Risk index
10 - 2.2.3 Value and nature of building and contents
10 - 2.2.4 Relative exposure
10 - 2.2.5 Frequency and severity of thunderstorms
10 - 2.3 NEED FOR PROTECTION OF PERSONS AND EQUIPMENT WITHIN BUILDINGS
15 - SECTION 3 BEHAVIOURAL PRECAUTIONS FOR PERSONAL SAFETY
15 - 3.1 SCOPE OF SECTION
15 - 3.2 PERSONAL CONDUCT
15 - 3.3 EFFECT ON PERSONS AND TREATMENT FOR INJURY BY LIGHTNING*
16 - SECTION 4 PROTECTION OF BUILDINGS
16 - 4.1 SCOPE OF SECTION
16 - 4.2 ZONES OF PROTECTION
16 - 4.2.1 Basis of recommendations
16 - 4.2.2 Required protection
16 - 4.3 METHODS OF PROTECTION
16 - 4.3.1 Structural steel-framed buildings
19 - 4.3.2 Buildings without structural steel frames
20 - 4.3.3 Structures with flammable or explosive atmosphere
20 - 4.4 MATTERS TO BE CONSIDERED WHEN PLANNING PROTECTION
20 - 4.4.1 Structures to be erected
20 - 4.4.2 Design considerations
23 - 4.5 MATERIALS
23 - 4.5.1 General
23 - 4.5.2 Corrosion
25 - 4.6 FORM AND SIZE OF CONDUCTORS
25 - 4.6.1 Factors influencing selection
25 - 4.6.2 Electrical and thermal considerations
25 - 4.6.3 Mechanical strength and corrosion considerations
26 - 4.7 JOINTS
26 - 4.7.1 Effectiveness of joints
26 - 4.7.2 Protective covering
26 - 4.8 FASTENERS
26 - 4.9 AIR TERMINATIONS
26 - 4.9.1 General requirements
27 - 4.9.2 Protection of roofs
27 - 4.9.3 Protection of the sides of tall buildings
28 - 4.10 DOWNCONDUCTORS
28 - 4.10.1 Structures- General
28 - 4.10.2 Route
29 - 4.10.3 Mechanical damage
29 - 4.11 TEST LINKS
29 - 4.12 EARTH TERMINATIONS
29 - 4.12.1 General principles
29 - 4.12.2 Resistance to earth
31 - 4.12.3 Common earthing electrode and potential equalization
31 - 4.13 EARTHING ELECTRODES
31 - 4.13.1 General considerations
31 - 4.13.2 Connections to electrodes
32 - 4.13.3 Inspection and testing of electrodes
32 - 4.14 METAL IN AND ON A STRUCTURE
32 - 4.14.1 Use of metal in or on a structure as a part of the lightning protection system
32 - 4.14.2 Prevention of side flashing
35 - SECTION 5 PROTECTION OF PERSONS AND EQUIPMENT WITHIN BUILDINGS
35 - 5.1 SCOPE OF SECTION
35 - 5.2 NEED FOR PROTECTION
35 - 5.3 MODES OF ENTRY OF LIGHTNING IMPULSES
36 - 5.4 GENERAL CONSIDERATIONS FOR PROTECTION
38 - 5.5 PROTECTION OF PERSONS WITHIN BUILDINGS
38 - 5.5.1 Objectives of protection
38 - 5.5.2 Installation of equipotential bonding
39 - 5.6 PROTECTION OF EQUIPMENT
39 - 5.6.1 General
39 - 5.6.2 Primary protection
39 - 5.6.3 Secondary protection
44 - SECTION 6 PROTECTION OF MISCELLANEOUS STRUCTURES AND PROPERTY
44 - 6.1 SCOPE OF SECTION
44 - 6.2 STRUCTURES WITH RADIO AND TELEVISION AERIALS
44 - 6.2.1 Indoor aerial system
44 - 6.2.2 Outdoor aerials on protected structures
44 - 6.2.3 Aerials on unprotected structures
44 - 6.2.4 Earthing of radio systems
44 - 6.3 STRUCTURES NEAR TREES
44 - 6.4 PROTECTION OF TREES
45 - 6.5 CHIMNEYS, METAL GUY-WIRES OR CABLES
45 - 6.5.1 General
45 - 6.5.2 Metal ladders and metal linings
45 - 6.5.3 Reinforced concrete chimneys
45 - 6.6 PROTECTION OF MINES
45 - 6.6.1 Factors influencing need for protection
45 - 6.6.2 Object of recommendations
45 - 6.6.3 Underground workings
46 - 6.6.4 Surface workings
46 - 6.6.5 Lightning detector
46 - 6.7 PROTECTION OF BOATS
46 - 6.7.1 General
46 - 6.7.2 Elements of the protection system
47 - 6.7.3 Installation recommendations
47 - 6.7.4 Precautions for persons and maintenance suggestions
47 - 6.8 FENCES
48 - 6.9 MISCELLANEOUS STRUCTURES
48 - 6.9.1 Large tents and marquees
48 - 6.9.2 Small tents
48 - 6.9.3 Metal scaffolding and similar structures, including overbridges
48 - 6.9.4 Tall metal masts, towers, cranes and revolving and travelling structures
49 - 6.10 PROTECTION OF HOUSES AND SMALL BUILDINGS
49 - 6.10.1 General considerations
49 - 6.10.2 Air termination for the building
49 - 6.10.3 Provision of downconductors for the building
49 - 6.10.4 Provision of earthing electrodes
50 - SECTION 7 PROTECTION OF STRUCTURES WITH EXPLOSIVE OR HIGHLY- FLAMMABLE CONTENTS
50 - 7.1 SCOPE OF SECTION
50 - 7.2 GENERAL CONSIDERATIONS
50 - 7.2.1 Acceptable risks
50 - 7.2.2 Protection required
50 - 7.2.3 Electrostatic shielding
50 - 7.3 AREAS OF APPLICATION
50 - 7.4 EQUIPMENT APPLICATION
50 - 7.4.1 Earth bosses
51 - 7.4.2 Bonding conductors
51 - 7.4.3 Sizes of tapes
51 - 7.4.4 Downconductors (see Clause 4.10)
51 - 7.4.5 Air terminations (see Clause 4.9)
51 - 7.5 SPECIFIC OCCUPANCIES
51 - 7.5.1 Protection of steel tanks
53 - 7.5.2 Installations handling crude oil and products
53 - 7.5.3 Aircraft fuelling and de-fuelling
53 - 7.5.4 Structures with explosive or highly flammable contents
55 - SECTION 8 INSTALLATION AND MAINTENANCE PRACTICE
55 - 8.1 WORK ON SITE
55 - 8.2 INSPECTION
55 - 8.3 TESTING
55 - 8.4 RECORDS
55 - 8.5 MAINTENANCE
56 - APPENDIX A - THE NATURE OF LIGHTNING AND THE PRINCIPLES OF LIGHTNING PROTECTION
56 - A1 SCOPE OF APPENDIX
56 - A2 THE NATURE OF LIGHTNING
56 - A2.1 Nature of lightning
56 - A2.2 The lightning attachment process
56 - A2.3 Thunderstorm and lightning occurrence
57 - A3 EFFECTS OF LIGHTNING
58 - A4 POTENTIAL DIFFERENCES CAUSED BY LIGHTNING
58 - A4.1 General
59 - A4.2 Earth currents
59 - A4.3 Side-flash
59 - A4.4 Potential (voltage) differences
59 - A5 PRINCIPLES OF LIGHTNING PROTECTION
59 - A5.1 Purpose of protection
59 - A5.2 Interception of lightning
59 - A5.3 Determination of lightning strike attachment points to buildings
61 - A5.4 Protection of the sides of tall buildings
62 - A5.5 Safe discharge to earth
62 - A5.6 Potential equalization
62 - A6 ELEMENTS OF A PROTECTION SYSTEM
63 - A7 VARIATION IN THE LEVEL OF LIGHTNING PROTECTION PROVIDED
64 - A8 COLLECTION VOLUME DESIGN
64 - A8.1 Introduction
64 - A8.2 Basis of design method
65 - A8.3 Practical application
65 - A8.4 References
68 - APPENDIX B - NOTES ON EARTHING ELECTRODES AND MEASUREMENT OF EARTH IMPEDANCE
68 - B1 GENERAL
68 - B1.1 Function of earth electrode system
68 - B1.2 Factors influencing earth impedance
68 - B1.3 Measures for reducing earth impedance
68 - B2 RESISTIVITY OF SOIL
68 - B2.1 General
70 - B2.2 Artificial reduction of soil resistivity
70 - B2.3 Determining soil resistivity by test
70 - B3 CALCULATION OF EARTH RESISTANCE OF AN ELECTRODE
71 - B4 USE OF ELECTRODES IN PARALLEL
72 - B5 DRIVEN OR DRILLED ELECTRODES
72 - B5.1 General
72 - B5.2 Safety
72 - B5.3 Installation
72 - B5.4 Materials for electrodes
72 - B5.5 Electrode diameter
72 - B5.6 Depth of installation
73 - B5.7 Sleeving of exposed part of vertical electrode
73 - B5.8 Comparison with other electrode types
73 - B6 BURIED STRIP ELECTRODES
74 - B7 BURIED PLATE ELECTRODES
74 - B8 CONCRETE FOOTING ELECTRODES
74 - B9 INSPECTION AND MAINTENANCE OF ELECTRODES
75 - B10 MEASUREMENT OF SOIL RESISTIVITY, EARTH ELECTRODE RESISTANCE AND EARTHING SYSTEM IMPEDANCE
75 - B10.1 Determination of soil resistivity by test
75 - B10.2 Electrode resistance testing – three-pin method
77 - B10.3 Isolation of surge impedance of an electrode system from other fortuitous earth paths
79 - APPENDIX C - THE CALCULATION OF LIGHTNING DISCHARGE VOLTAGES AND REQUISITE SEPARATION DISTANCES FOR ISOLATION OF A LIGHTNING
79 - C1 GENERAL
80 - C2 TRANSIENT VOLTAGE CALCULATIONS BY TRAVELLING WAVE ANALYSIS
80 - C2.1 Simplified travelling wave characteristics
81 - C2.2 Surge voltage calculation by lattice diagram
82 - C3 SURGE VOLTAGE CALCULATIONS BY LUMPED CIRCUIT APPROXIMATIONS
86 - APPENDIX D - WAVESHAPES FOR ASSESSING THE SUSCEPTIBILITY OF EQUIPMENT TO TRANSIENT OVERVOLTAGES DUE TO LIGHTNING
90 - APPENDIX E - ALTERNATIVE DETERMINATION OF INDEX E BASED ON LIGHTNING FLASH DENSITY/ENERGY DATA
90 - E1 INTRODUCTION
90 - E2 DERIVATION OF INDEX E BASED DIRECTLY ON RECORDED LIGHTNING FLASH DENSITY
90 - E3 DERIVATION OF INDEX E BASED ON RECORDED INCIDENCE OF GROUND FLASHES OF ABOVE-AVERAGE ENERGY.
91 - E4 LIGHTNING FLASH DENSITY/ENERGY DATA FOR SOUTH EAST QUEENSLAND AND NORTHERN NEW SOUTH WALES
96 - APPENDIX F - REFERENCED DOCUMENTS

Sets out guidelines for the protection of persons and property from hazards arising from exposure to lightning. In particular, it covers: the protection of persons from both direct and indirect effects of a lightning strike; the protection of various buildings and structures from the risk of physical damage or fire; and the protection of sensitive equipment from overvoltages resulting from a lightning strike to a building or its associated services. The nature of lightning and the principles of lightning protection are discussed and guidance is given to assist in determining if a particular building or structure should be protected. Identical with NZS 1768:1991 and produced as a Joint Australian/New Zealand Standard.

This Standard sets out guidelines for the protection of persons and property from hazards arising from exposure to lightning. The recommendations specifically cover the following applications:(a) The protection of persons, both outdoors, where they may be at risk from the direct effects of a lightning strike, and indoors, where they may be at risk indirectly as a consequence of lightning currents being conducted into the building.(b) The protection of a variety of buildings or structures, including those with explosive or highly-flammable contents, and mines.(c) The protection of sensitive electronic equipment (e.g. facsimile machines, modems, computers) from overvoltages resulting from a lightning strike to the building or its associated services.The nature of lightning and the principles of lightning protection are discussed and guidance is given to assist in a determination of whether protective measures should be taken.The recommendations in this Standard do not apply to the protection of large scale power or communications systems, nor do they apply to the protection of special structures such as oil and gas platforms.

Under Revision see DR 02359 In Australia First published as AS MC1-1969.Revised and redesignated AS 1768-1975.Second edition 1983.Third edition 1991. In New Zealand In Australia First published as AS MC1-1969. Revised and redesignated AS 1768-1975. Second edition 1983. Third edition 1991. In New Zealand