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PART 3
SCIENTIFIC BACKGROUND
Part 3: Scientific background 2 May 2001
Part 3: Scientific background 3 May 2001
Reading guidance
This is Part 3 of the set of publications entitled ‘Life cycle assessment: An operational guide to the ISO
standards’. Part 1, ‘LCA in perspective’, is a short booklet describing in broad terms the purpose, role,
fields of application and limitations of life cycle assessment. It is targeted principally at parties
commissioning an LCA and parties using the results of such an analysis. Part 2 consists of two parts:
the actual Guide (2a) and an Operational annex (2b). Its target audience is those concerned with actual
execution of an LCA. Depending on context and complexity, this may be one person or an entire
research team with various backgrounds, such as process technology, product design, abatement
technology, ecotoxicology, and so on.
The present Part 3, ‘Scientific background’, sets out the foundations and arguments for the
methodological choices made, the alternative choices that are available, and much more. It is designed
to encourage scientific debate on the progress made to date and as a reference book for those wishing
to learn more about the rationale behind the rules presented in the Guide.
The presentation of the proposed working method for LCA is structured according to a framework on
which there is worldwide consensus and which forms the basis of a series of ISO standards. This
framework breaks down the LCA procedure into four distinct phases:
- Goal and scope definition;
- Inventory analysis;
- Impact assessment; and
- Interpretation;
each of which comprises a number of distinct steps. The present Part has a chapter devoted to each of
these four phases.
By way of introduction, Chapter 1 discusses the general theoretical foundations and modeling aspects of
LCA, considers procedural aspects and outlines the stepwise structure of the present LCA Guide.
Chapters 2 to 5 are then devoted to the four phases and constituent steps of an LCA, as specified
above, with each step discussed according to a fixed format (as far as is useful):
- topic, providing a brief description of the scope and function of the step;
- developments in the last decade, providing an as comprehensive as possible description and
analysis of relevant developments since 1992;
- prospects, describing developments anticipated in the future;
- conclusions, presenting conclusions on the best available practice for the step in question, as
recommended in this Guide;
- research recommendations, outlining suggested topics for further research.
Chapter 6 provides a comprehensive bibliography of all the literature sources cited in the preceding
chapters.
Appendix A lists all the external contributors to this guide, while Appendices B and C report the results
of two desk studies performed as part of the preparatory work for this guide. Appendix B reviews the
desk study on the fields of application for LCA, Appendix C that on partitioning economic inputs and
outputs to product systems (allocation).
Part 3: Scientific background 4 May 2001
CONTENTS
 
READING GUIDANCE 3
CONTENTS 4
1. GENERAL INTRODUCTION 7
1.1 GENERAL THEORETICAL FOUNDATIONS OF LCA 10
1.1.1 Introduction 10
1.1.2 The purpose of LCA 11
1.1.3 The questions addressed by LCA 12
1.1.4 The methodology of LCA 13
1.2 MODELING ASPECTS OF LCA 14
1.2.1 Introduction 15
1.2.2 Theoretical modeling aspects 15
1.2.2.1 The reality behind the model 15
1.2.2.2 The need for a simple model 17
1.2.2.3 Main model simplifications 18
1.2.3 Practical modeling aspects 21
1.2.3.1 Potential versus actual impacts 21
1.2.3.2 Beyond the default simplifications 22
1.2.3.3 Spatial differentiation 23
1.2.3.4 Average and marginal processes and average and marginal process data 26
1.2.3.5 Quantitative and qualitative information and notation 29
1.2.3.6 Reporting of LCA 32
1.2.3.7 Software for LCA 34
1.3 MANAGEMENT OF LCA PROJECTS: PROCEDURES 34
1.3.1 Introduction 34
1.3.2 Decision-making based on a process approach 36
1.3.3 Designing the decision-making process 37
1.3.4 Implementation of LCA tasks 39
1.3.5 Representation of interests 41
1.3.6 Progress of the decision-making process 43
1.3.7 Process outcome 45
1.4 STEPWISE STRUCTURE FOR ENVIRONMENTAL LIFE-CYCLE ASSESSMENT 46
1.4.1 Goal and scope definition 46
1.4.2 Inventory analysis 49
1.4.3 Impact assessment 53
1.4.4 Interpretation 57
1.5 FURTHER READING GUIDANCE 58
2. GOAL AND SCOPE DEFINITION 62
2.1 INTRODUCTION 62
2.2 GOAL DEFINITION 63
2.3 SCOPE DEFINITION 67
2.4 FUNCTION, FUNCTIONAL UNIT, ALTERNATIVES AND REFERENCE FLOWS 76
3. INVENTORY ANALYSIS 85
3.1 GENERAL INTRODUCTION 85
3.2 ECONOMY - ENVIRONMENT SYSTEM BOUNDARY 87
3.3 FLOW DIAGRAM 92
Part 3: Scientific background 5 May 2001
3.4 FORMAT AND DATA CATEGORIES 93
3.5 DATA QUALITY 99
3.6 DATA COLLECTION AND RELATING DATA TO UNIT PROCESSES 104
3.7 DATA VALIDATION 109
3.8 CUT-OFF AND DATA ESTIMATION 109
3.9 MULTIFUNCTIONALITY AND ALLOCATION 116
3.10 CALCULATION METHOD 134
4. IMPACT ASSESSMENT 136
4.1 GENERAL INTRODUCTION 136
4.1.1 International organisations involved 137
4.1.2 ISO 14042 requirements 138
4.1.3 Relation between ISO and SETAC Working Group on LCIA 141
4.2 SELECTION OF IMPACT CATEGORIES 141
4.3 SELECTION OF CHARACTERISATION METHODS: CATEGORY INDICATORS,
CHARACTERISATION MODELS AND FACTORS 150
4.3.1 Depletion of abiotic resources 154
4.3.2 Depletion of biotic resources 159
4.3.3 Impacts of land use 161
4.3.3.1 Land competition 170
4.3.3.2 Loss of biodiversity and loss of life support functions 172
4.3.4 Desiccation 184
4.3.5 Climate change 185
4.3.6 Stratospheric ozone depletion 188
4.3.7 Human toxicity 190
4.3.8 Ecotoxicity 204
4.3.9 Photo-oxidant formation 212
4.3.10 Acidification 217
4.3.11 Eutrophication 222
4.3.12 Waste heat 225
4.3.13 Odour 227
4.3.14 Noise 229
4.3.15 Impacts of ionising radiation 232
4.3.16 Casualties 239
4.3.17 Interventions for which characterisation factors are lacking 240
4.3.18 Economic flows not followed to system boundary 241
4.4 CLASSIFICATION 241
4.5 CHARACTERISATION 243
4.6 NORMALISATION 244
4.7 GROUPING 247
4.8 WEIGHTING 249
5. INTERPRETATION 253
5.1 GENERAL INTRODUCTION 253
5.2 CONSISTENCY CHECK 255
5.3 COMPLETENESS CHECK 255
5.4 CONTRIBUTION ANALYSIS 256
5.5 PERTURBATION ANALYSIS 256
5.6 SENSITIVITY AND UNCERTAINTY ANALYSIS 257
5.7 CONCLUSIONS AND RECOMMENDATIONS 261
6. REFERENCES 263
ANNEX A: CONTRIBUTORS 277
1. STEERING COMMITTEE 277
Part 3: Scientific background 6 May 2001
2. THINK-TANK 277
3. SUPERVISORY COMMITTEE 278
4. INTERNATIONAL OBSERVERS GROUP 278
APPENDIX B: AREAS OF APPLICATION OF LCA 279
1. INTRODUCTION 281
2. THE ENVIRONMENTAL TOOLBOX 281
2.1 INTRODUCTION 281
2.2 REVIEW OF TOOLS 281
2.3 COMPARISON OF TOOLS 283
3. LCA FIELDS OF APPLICATION: A CLOSER LOOK 284
3.1 INTRODUCTION 284
3.2 FEATURES OF LCA 284
3.3 ISSUES OF CONCERN 286
3.4 DEMARCATING THE SCOPE OF LCA 289
4. NEW FIELDS OF LCA APPLICATION 290
4.2 Lifestyle 291
4.3 Infrastructure and transportation 292
5. CONCLUSIONS AND RECOMMENDATIONS 293
APPENDIX C: PARTITIONING ECONOMIC INPUTS AND OUTPUTS TO PRODUCT
SYSTEMS 295
1. INTRODUCTION: PROBLEM DEFINITION AND THE ISO PARTITIONING PROCEDURE 296
2. BASIC APPROACHES TO ALLOCATION AND THE QUESTION OF SYSTEM BOUNDARIES 298
3. AVOIDING ALLOCATION (STEP 1.2 OF ISO 14041) 305
4. ALLOCATION ACCORDING TO PHYSICAL RELATIONSHIPS (STEP 2 OF ISO 14041) 308
5. ECONOMIC ALLOCATION (STEP 3 OF ISO 14041) 309
5.1 INTRODUCTION 309
5.2 EXAMPLES OF ECONOMIC ALLOCATION 310
 
Part 3: Scientific