An Engineer’s View of Human Error – Third Edition

An Engineer’s View of Human Error – Third Edition
اسم المؤلف
Trevor Kletz
التاريخ
13 ديسمبر 2023
التصنيف
المشاهدات
215
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An Engineer’s View of Human Error – Third Edition
Trevor Kletz
The theme of this book – Try to changesituations, not people

Contents
Foreword tothethird edition vi
1 Introduction
11 Accept men as we findthem
1 2 Meccano ordofs? 3
1 3 Typesofhuman error 4
1.4 Twosimpleexamples 6
1.5 Accident investigation 8
16 Astory 9
1 7 Researchonhuman error 10
2 Accidents causedbysimple slips 11
2 1 Introduction 11
22 Forgetting toopenorcloseavalve 13
23 Operatingthewrongvalve 21
24
Pressingthewrong button 25
25 Failuresto notice 29
2.6 Wrong connections 31
27 Errorsincalculations 32
2.8 Other medicalerrors 34
2.9 Railways 35
210 Otherindustries 41
211
Everydaylife(and typing) 43
2.12 Fatigue 45
3 Accidentsthatcouldbeprevented bybeftertrainingorinstructions 48
3 1 Introduction 48
32 Three Mile Island 50
33 Otheraccidentsthat could be
prevented byrelatively sophisticated training 53
34 Accidentsthat could be
prevented byelementary training 62
35 Contradictory instructions 65
36
Knowledge ofwhat we don’t know 66
vii37 Some simpleways ofimprovinginstructions 67
3.8 Training orinstructions? 72
3.9 Caseswhentrainingisnot thebestanswer 74
4 Accidentsduetoalackofphysicalormental ability 78
41
People asked to do thephysicallydifficultorimpossible 78
42 People askedtodo thementallydifficultorimpossible 80
4.3 Individual traits andaccident proneness 85
4.4 Mind-sets 88
5 Accidents due tofailures tofollow instructions 97
5.1 Accidentsduetonon-compliance bymanagers 99
5.2 Accidents duetonon-compliance byoperators 103
5.3 Actionstoimprovecompliance 107
54 Alienation 109
55
Postscript 110

  1. Accidentsthatcouldbyprevented bybettermanagement 112
    6.1 An accidentcaused byinsularity 114
    62 An accident duetoamateurism 115
    6.3 The fire at King’s Crossrailway station 116
    64 TheHeraldofFreeEnterprise 117
    65 The
    Clapham Junction railway accident 118
    6.6 PiperAlpha 120
    67 What morecan seniormanagersdo? 120
    6.8 Themeasurement ofsafety 125
    6.9 Conclusions 127
    7 Theprobability ofhumanerror 129
    7.1 Whydo we needtoknow human errorrates7 130
    72 Human errorrates —asimpleexample 132
    73 Amorecomplexexample 132
    7.4 Otherestimatesofhuman errorrates 136
    75 Two moresimpleexamples 141
    7.6 Buttonpressing 144
    7.7 Non-process operations 146
    78 Train drivererrors 147
    7.9 Some pitfalls inusingdata on humanreliability 147
    7.10 Dataonequipment maybedata onpeople 149
    Viii7.11 Whomakes theerrors7 151
    7.12 Conclusions 151
    8 Some accidentsthatcouldbeprevented bybetterdesign 154
    8.1 Isolation of protective equipment 155
    82 Better information
    display 156
    8.3 Pipe failures 156
    8.4 Vessel failures 159
    85 TheSellafield leak 159
    8.6 Otherdesign errors 161
    87
    Conceptual shortcomings 162
    8.8 Problems of
    design contractors 165
    89 Domestic accidents 166
    9 Some accidentsthatcouldbeprevented bybetterconstruction 168
    91 Pipefailures 168
    9.2 Miscellaneous incidents 170
    93 Prevention ofconstruction errors 173
    10 Some accidentsthatcouldbeprevented bybettermaintenance 175
    10 1 Incidents which occurred becausepeopledid notunderstand how
    equipmentworked 175
    10.2 Incidents which occurred becauseof
    poormaintenance practice 178
    103 Incidents dueto
    gross ignorance orincompetence 180
    104 Incidents which occurred becausepeopletook shortcuts 181
    105 Incidents which could beprevented bymorefrequentorbettermaintenance 183
    10.6 Can we avoidtheneedforsomuch maintenance? 185
    11 Some accidents thatcouldbeprevented bybettermethods
    ofoperation 187
    111 Permits-to-work 187
    112 Tanker incidents 189
    113 Some incidents that could be
    prevented bybetterinstructions 192
    114 Some incidents
    involving hoses 193
    11.5 Communication failures 194
    11.6 Examplesfrom therailways 199
    11.7 Simple causesinhightechindustries 201
    12 Errors incomputer-controlled plants 203
    12.1 Hardware failures 204
    122 Software errors 205
    123 Specification errors 207
    12.4 Misjudging responsestoacomputer 210
    ix125 Enteringthewrongdata 213
    126 Failurestotelloperators ofchangesindataorprograms 214
    12.7 Unauthorized interference withhardware orsoftware 214
    128 Thehazardsofoldsoftware 217
    12.9 Otherapplications ofcomputers 217
    12.10Conclusions 218
    13 Personal andmanagerial responsibility 221
    13.1 Personalresponsibility 221
    132 Legalviews 223
    133 Blame inaccident investigations 227
    134
    Managerial wickedness 228
    135 Managerial competence 229
    136 Possibleandnecessary 231
    14 Theadventures ofJoeSoapand John Doe 234
    15 Somefinal thoughts 254
    Postscript 257
    Appendix 1 —Influences onmorale 258
    Appendix2—Somemythsofhuman error 26]
    Appendix 3—Somethoughts on sonataform 269
    Further reading 271
    Index 273
    xIndex
    A
    Aberfan
    ability,lackof
    Aborigmes
    access
    accidentinvestigation
    accidentstatistics
    accident—prone
    acetone
    2, 99, 118, 125,
    129, 155, 178, 189
    Australia 123, 148
    123 auto—pilot 11—12
    79 automatic train protection 39—40
    automation 83—84, 104, 116,
    130—131, 191,253,263
    andpeople compared 84, 143,
    199 207—208, 211
    acids 45, 53,58. 192—194, 199
    254
    32,53
    9, 17,41, 146—147,
    161,213—214,227
    Aisgill 38
    alarmoverload 80—82
    alarms 21—22,53,58, 65—66, 74, 80—81,
    100—101, 105, 125, 130, 149—150,
    155,204—205, 207,210-211,263
    alertness 83—84, 198,215
    alienation 109—110
    amateurism 115
    ambulances 83
    Amish
    ammonia
    anaesthetics
    appearance, incorrect
    asbestos
    assembly
    incorrect
    probability oferrors
    attitudes
    B
    back injuries
    batchprocesses
    errors, probability of 140, 143—144
    behavioural safetytraining 12, 75,
    176, 229
    behavioural science techniques 107—109
    bellows 150, 159, 169, 173, 261—262
    BelvoirCastle 110
    beveragemachines 25—26, 144—146, 150
    Bhopal 121
    Bible 74,226
    bicycles 85
    110 ‘black book’ 53
    blackbox 207,209
    blame 8—9, 37,97—98. 104, 113, 182,
    213, 221,225—229,263,266—267
    blind
    eye 65,99, 104, 119, 124,225,263
    boilers (seealso waste heatboilers) 17.
    84, 105,155,179,184—185
    bolts
    botching 63, 169
    audits
    184, 229
    78—94
    122—123, 227
    1,87
    12, 85—88
    ‘ActsofGod’
    agitation
    aircraft
    75
    169,190
    31,35
    34
    225
    121
    157, 161
    146
    75, 257
    175
    273AN ENGiNEERS ‘flEE OF NOMAN ERROR
    box girderbridges 57 colour—coding 22—24,26, 30, 32,74,
    brakes 200 175,179,212
    breathingapparatus 62,78, 161, colunmsupports 91—92
    179, 182 commonlaw 76
    bridges 57 commonmodefailure 22
    burstingdiscs 251 cornmumcation 119, 124. 208—210
    buttons 25—29, 144—146,250 byradio 199
    probabilityofpressingerrors144—146 verbal 198—199
    Byng,Admiral 74 written 194—197
    complexity 22, 121, 163. 266
    compressed air 61, 161,179,
    194,200,209,265
    C compressed gases 72
    cablerailways 9 powerof 54
    cables 176 compressorhouses 170
    calculation errors 32—34,213 compressors 78, 169—170
    cars 6. 16,43, 63—64, 105, 151, 265 computerdisplays 211
    causes computers 8, 81,203—218
    underlying 114-120.122—123 calculationsby 217
    versus actions 255 capability exaggerated 207,215
    caustic soda 193 errorsinentries 212—214,216
    chance 86—87 hardware failures 204—205
    Channel Tunnel 65—66 responsesto 210—213
    Chazops 209 retentionofdata 211
    check—lists 16 software errors 205—206
    checks 99, 104—107, 117—118, specification errors 208—210
    147—149, 155, 169, 181, 196. 201 condensate 198
    weakness of 119 connections, wrong 31
    chemicalburns 20, 58, 182—183 connectorsforhoses 31—32,187—189.
    Chemobyl 52, 101—102 193—194
    Chinley 38 conspiracy 94
    chlorine 62 construction 57,81—82, 157,
    chloroform 31 168—173,261
    chokes 50, 53—55, 91 contamination 192
    clamps 43 contractors 56, 64, 110, 115, 165, 172
    ClaphamJunction 45, 118—119,228 contradictory mstructions 65—66, 73
    classification systems 4,7, 26 controlrooms 27, 131—132
    cleaning 193 corrosion 104, 157, 201
    clocks 43—44 ofprocedures 4
    clumsiness 79 costs 40, 113, 121, 125, 185
    cognitivedissonance 94 cranes 17,27, 57,78, 84
    cokers 89—90 creativity 267
    collierytips 184 crime 221—226
    274INDEX
    culture 88, 109, 112, 176, electncalareaclassification 164
    258—260,265 electrical equipment 64.79, 148, 164,
    cylinders 62, 78, 177-479,245 178,204,244
    electricity, isolation of 17. 148
    D emergency evacuation 85
    databases 124—125 entry toconfinedspaces 71. 179,196,
    dates 214 247.251
    dead—ends 169 equipment
    debottlenecking 164 failures 149—150
    defenceindepth 79 flameproof 178
    demanning (see manpower, identification of 180, 187—189,235,
    reductions in) 248,250
    demolition 44 opening of 13—16,209
    design 2—4,12. 16,20—23.32—34,41, errors(seealsotraindrivererrors)
    43, 57,66, 80—81,91, 115, inbatchprocesses 140, 143—144
    117—118, 154—166, 170, 173, 265 bymanagers 112—125
    alternatives 23—24,121,162—165 definition of v
    buildandmaintain’ 185 medical 31, 34—35,214
    designliaison 164—165, 172 innumbers 30—31
    diagnosis 48, 52,94 measurement 146
    dieselengines 90, 115 opportunities for 3
    dimensions, estimatrnn of 85 probability of 6, 16,26, 90,
    directors, responsibilities of 112—125 120,129—152
    discretion 73 examples 131—146
    discussions 50, 56,71, 84,98. 103, 155 limitations 129—130, 147—151
    distillation columns 17,54, 132 reasons for 130—131
    distractions 26, 130, 146 insoftware 205—206
    documents, ancient 93 recoveryfrom 27
    dolls 3 escalators 116
    domestic accidents 43—44, 166, 240 ether 255
    drain valves 17—21, 63, 183,235,253 ethylene 31—32,91, 114. 163
    drowning 166 ethyleneoxide 163
    drums 30,56,64 events,rare,detectionof 82
    duplication, effecton eveiydayerrors 12
    probability oferror 147—149 everydaylife 11
    dusts 61, 100, 201 evidenceignored(seemind—sets)
    expectations 84—85
    experiments 102
    E expertsandamateurs 115
    education 48—76, 124 explosion venting 170
    of
    managers 113, 125 explosions 31—32,58,61, 64.66—67,71,
    Einstellung 88 80,90, 100, 105, 109, 114, 120,
    electricplugs 74 163, 170—171, 184,202,211,238,242
    275AN ENGINEER’SVIEW OF HUMAN ERROR
    F hazard and operability
    falls 105, 166 studies (Hazop) 20, 61—62,91, 155,
    fatalaccident rate 231 160, 165,205,207—210,
    fatigue 45—46, 118, 166 212—213, 232, 261
    ofmetals 168 hazards, hidden(seealso
    fencing(ofmachinery) 224 forgottenhazards) 113
    Feyzin 55—56 Hazop(seehazard andoperability
    filters 13—15,30, 54, studies)
    61, 109. 177, 209 Healthand Safety atWorkAct 229
    fires 20,28, 32,36, 55,65—66, HeraldofFreeEnterprise 117—118
    72, 100, 109, 115—1 16, 120, HomeGuard 48
    125, 156—157, 166, 172, 175, hoses 32, 61, 187—189,
    183, 191, 193, 199, 244, 261 193—194.200,243,265
    fire—fighting 44, 85, 222 hydrogen fluoride 202
    flamearresters 99, 184 hydrogen sulphide 78
    flameproofequipment 178 hygienic factors 258—260
    flarestacks 45, 91
    Flixborough 66—67,121,163,215 I
    foam—over 239 ICI 1,231
    forceand
    pressure confused 54 identification ofequipment 180,
    forgery 222 187—189, 235, 248, 250
    forgetfulness 11—46 ignition 114, 116, 171, 199, 261
    forgottenhazards 53, 62,64, 72, 109, ignorance 53—67, 103, 164,
    119, 123—124, 164, 175—180, 183. 265
    184, 234—253, 264 indicatorlights 17—18
    Freud 12 information 267
    friendlydesign(seeuser-friendly design) information display
    full—scale deflection 91 (seealsolabels) 126, 156
    furnaces 29, 90, 170, 244 information overload 80—81
    information retrieval 124
    inherently saferdesign 52, 120—121,
    G 151—152, 162—163,
    gaskets 180, 252 165, 206, 265—266
    ‘glassboxes’ 209 initiative 5,98, 106
    goodengineering practice 168 insects 49
    gravity 2 inspection 56, 125, 168, 173,
    greyhairs 4 178—179, 261
    instability(ofprocesses)
    (seealso runaway reactions) 101—102
    H instructions 2—7.15,20,48—76, 107,
    habits 84—85 113, 119. 192—193,
    hangers 176 206—208. 230
    Harrow 39 contradictory 65, 73
    276lost
    ways ofimproving
    instrumentfailure
    insularity
    intention changes
    interlocks (see alsotrips)
    inventories, needtoreduce
    J
    K
    keys(seebuttons)
    kinetichandling
    King’s Cross
    knowledge, failuretouse
    knowledge—basedtasks
    ontowater
    lecturedemonstrations
    legalresponsibility
    libranes
    liftinggear
    lightbulbs
    liquefiedflammable gas
    liquefiedpetroleum gas
    (seealso propane)
    liquidtransfers
    lithiumhydride
    Lithuania
    lost—timeaccidentrate
    lubrication
    M
    machines andpeople compared 83—84
    maintenance 4,17,27—29,99, 175—185
    avoiding theneed 185
    ofinstructions 71
    isolationfor 17
    preparation for 16, 27—29,32,72,
    81—82. 103—104, 115. 148,
    180—183, 187—192,215,250
    qualityof 63, 149—150, 183—185
    management 2,5
    education
    errors
    managenalresponsibility
    managers
    responsibilities of
    senior, actionspossibleby
    manpower, reductions in
    112—125
    120
    60,67,
    122—123, 178
    manualhandling 75
    materials ofconstruction 150, 156, 161,
    169—170, 172, 201
    187—191 effectoftemperatureon 54,58
    measurement errors, probabilityof 146
    measurement ofsafety 125
    Meccano 3
    mechanical handling 198
    81 medicalerrors 31,34—35,214
    45 Melbourne 57
    221—226
    memory (see forgotten accidents)
    222 mercenaries 110
    methanol 193
    150 methodsofworking 17
    100,190 mind—sets 38, 88—94,163, 180, 192
    53,56
    67—77
    150
    114
    182—183
    15, 18—20,22,
    41, 204—206,
    214—216, 266
    121
    INDEX
    180
    192
    61—62
    216
    112—113,
    230,260
    150,201
    joints 34, 55, 114, 178—180, 183, 193
    judgement, premature 88—89
    75
    114, 116
    10,54—56
    5—6,72—74,
    [44,208
    L
    labels
    missing
    ladders
    lapsesofattention
    113, 125
    7, 112—125
    227—231
    law
    layout
    leaktesting
    leaks
    20, 26,28, 30, 53,60, 80,
    248,250,252,263,265
    21—22, 116
    30, 79, 105, 249
    vi,3—4,8—9.11—46,
    201,227
    225—226, 264
    22—23,75,79. 80, 115. 262
    31—32.34,58, 62, 109,
    114—115, 121, 159—160,
    176, 178, 182, 193—194,
    199,201.211,215,261
    43, 92—93, 179
    277RN ENGINEER’ S vIEW Oi RUMRN ERROR
    N
    27
    v, 5,78—94, 119
    205
    v,5—6,48—76
    91—92, 160, 172,
    206, 217, 264
    58—59,214
    214—216
    6
    39
    109—110,258—260
    107
    258—260
    269—270
    261—267
    navalwarfare 73, 83
    nearmisses 126
    negligence 266
    nitrogen 171, 187—189,237
    blanketing 164—165,204
    non—compliance(seeviolations)
    normalaccidents 266
    notices 20
    nuclear
    powerstations 50—52,101—102,
    151, 185,201—202, 216,266
    numbers, errors in 30—31
    nutsandbolts 179, 185
    0
    oldequipmentandsoftware 217
    open containers 236
    opening equipmentunderpressure 13—16
    opemngfullequipment 209
    options forthefuture 164
    organizational failures 101, 112
    overfilling 189—190. 193. 242
    overheating (seealso
    runawayreactions) 55, 101—102, 156,
    179, 196, 245
    p
    13—16,54,60,64,
    91, 100, 156, 159
    132—134
    163
    pacemakers 214
    Paddington 40
    paraffin 163
    parchments 93
    patience 94
    performance shaping factors 136
    permits—to—work 16—17,81—82,
    103—104, 125, 148. 171,
    179, 180—183, 187—192, 198
    personality, effectonaccidents of 86
    petrol 63, 80, 200
    green
    phonetic alphabet
    phosgene
    pictorialsymbols
    pigs
    piloterror
    pipesupports
    pipebridges
    PiperAlpha
    pipes
    plastic
    pitfalls
    poisoning
    policy
    statementsof 100
    polyethylene 31—32
    powder 61
    preparationformaintenance 250
    pressure,excessive
    (seeoverpressunng)
    pressurevessels (seealsoreactors)13—16
    probability data (see errors,
    probability of)
    problems, disappearance of 255
    propane 55
    overprcssuring
    probability of
    oxygen
    mirrorimages
    mismatches
    missiles
    mistakes
    modifications
    peoplenottold
    unauthorized
    monitoring
    Moorgate
    morale
    motivational appeals
    motivators
    music
    myths
    63
    198
    169
    196
    54
    41
    168—169
    33
    120
    150, 156,
    240,246
    58
    147—149
  2. 196
    120
    53—54,60, 66,
  3. 217
    278prosecution
    protective clothing
    protective equipment(see also
    alarms, automation,
    interlocks, trips) 4,38, 121—122,
    162—163, 165, 189—190,225
    isolation of
    protective systems
    protoplasm
    psychogemc illness
    pumps
    automatic start
    pushbuttons (see buttons)
    Q
    Qumtinshill
    R
    railways 32,35—40,45, 80,82—83,
    85—87, 104—105, 147,
    184—185, 198—201, 228, 253
    station fife
    Rasmussen Report
    reactions
    reactors(seealso nuclearpower
    stations) 18—20,25,27—30,63—65,
    72, 100, 163, 179, 192—193,
    207,211,212
    recordsheets 62,91
    recoveryfromerror 1,27, 146, 149
    refrigeration 91
    reliability,high 149
    reliefvalves 20—21,51, 55,57,90—91,
    104—105, 156, 159, 182, 184,
    190—191, 193,252—253, 266
    repeatedaccidents (seeforgotten
    hazards)
    research 10
    respirators 30
    responsibility
    227—231
    221
    151—152
    43
    61
    105
    122—123
    5—6,72—74, 144, 208
    97—110
    208,264
    66
    30,32, 53,63—65,
    207—208, 211
    251
    117—118
    36, 104, 181—183,189
    35—38, 83, 85—86,
    198, 200—201
    signals passedatdanger
    (SPADs) 38—40,80,82—83, 86,147
    similarnames 198—199
    simplicity 22, 121, 163
    ‘skillofthecraft’ 161,178
    skill—based tasks
    slips
    5—6. 72—74, 144
    vi,3—4,8—9,11—46,90,
    118—119,205,213,227,266
    103
    INDEX
    225 managerial
  4. 104, personal
    181—182,238 risks,tolerability of
    roadaccidents
    roadtankers
    roofs,falls through
    rootcauses
    155 rule—based tasks
    53 rules,violations of
    255 rules(see alsoinstructions)
    87 relaxationof
    20—21,53,62, 82, runaway reactions
    90, 182—183, 201
    141—142 rupture discs
    S
    safety advisers 264
    35—38 safetymanagement systems 122
    Salem 94
    sampling 238
    scaffolding 54
    scapegoats 73—74, 227, 230, 263
    scenesofaccidents, visitsto 105
    116
    scrap 241
    136, 138—139 ‘secondchance’design 160
    30,32 self—inflicted injuries 87, 258
    Sellafield 159—160
    seniority 116
    servicelines 116
    settling 160
    shipping
    shortcuts
    signalmen’serrors
    legal 221—226 smoking
    279AN ENGINEER’S VIEW OF HUMAN ERROR
    software,inscrutable
    software tests
    spacerockets
    SPADs(seesignals passed atdanger)
    Spain
    spares
    spellingerrors
    spilages
    staticelectricity
    steam
    steamdrums
    stirring(seeagitation)
    stores,unofficial
    stress
    stressconcentration
    supervision
    supervisors, overloading of
    systemfailures
    T
    effectonerrors
    tolerance (ofmisuse)
    ‘trackcircuits’
    190 traindrivererrors
    37, 118
    81
    tailors 9
    tankers 63, 189—192, 194,200,237,243
    tanks 56, 70, 80,91, 100,
    160,171-472,184
    overfilling, probability of 143
    taskoverload 81
    taskunderload 83—84
    tasks,difficult 98
    teamworking 60
    telephonenumbers 43
    temperature, effectonmaterials of54,58
    construction
    TESEO 136—137
    4, 21—22,62,72. 100—102,
    104—106, 119, 237—238, 242
    105—106
    205—206
    V
    vacuum
    valves(seealso
    drainvalves)
    263
    144
    121, 173
    37—38
    38—40,80,
    82—83,86. 104, 228
    147
    209 time
    205—206
    217
    106, 109
    7—8
    191, 204, 209, 237, 253
    13,60, 91, 180, 201. 240
    12,26, 43, 130,
    142—143, 146,166
    probability of
    training 2—8,11—12,48—76, 84,
    61 113, 124, 168, 173. 178—179.
    181, 189, 193, 215
    22 unavoidable dependence on 143
    transfers ofliquids 156, 159—160
    106 trapped liquids 109, 175
    trapped pressure 176, 183, 194, 243
    traps 26,41
    161 trips(seealsointerlocks) 21—22, 32, 50.
    100—101, 125, 131, 155—156,
    190, 204—206, 263. 266
    101 turbines 50
    tyres 156
    U
    unconscious mind 11—12
    unforeseen hazards 234—253
    unforeseen problems(see also
    modifications) 211—212
    university degreecourses iii
    user—friendly design 3,52, 120—121,
    206,212,248,249,
    251—252,266
    62
    13—24, 22—23,27—29,
    65, 79, 109. 131—132, 151,
    175, 177, 180. 182, 190,
    199,212,214—215
    vehicles (seealsocars) 84—86,156,
    198,245,262
    172, 178
    tests
    hail—clone
    software
    theft,avoiding
    THERP(TechniqueforHuman
    ErrorRatePrediction)
    ThreeMileIsland
    222
    136, 140
    280
    50—52 ventilation1I4DEX
    vents 20—22,63, 79, 90, 184, W
    193—194,236,239,246 wasteheatboilers 22, 74
    verbs,irregular 98,265 wastematerial 202
    vesselfailure 55, 159, 192—193, watchdogs 204—205
    212,246 watchmen 83
    vessels,sucked—rn 63, 184, 239 water 50—54. 172, 178,237,246
    violations v, 5—6,8,97—110,118—119, electrolysis of 104
    214—215, 227—229 waterhammer 60
    bymanagers 99—102 weldfailure 201
    byoperators t03—106 witches 94
    canprevent accidents 106 wrong method,rightanswer 267
    prevention of 97—98,107—109
    ofrules 97—110 V
    viruses 216 Yarranverbndge 57
    visibility 78—79 Yugoslavia 227—228

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