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3: Scientific background 49 May 2001
Goal and scope definition
Goal of the study
Scope of the study
Goal and scope definition
Function, functional
unit and reference
flow
Initial system
boundaries
Goal definition
Scope definition
Function, functional
unit, alternatives and
reference flows
Procedures
Description of data
categories
Criteria for initial
inclusion of inputs
and outputs
Data quality
requirements
Critical review
ISO 14041This Guide
Inventory analysis
Figure 1.4.1.1: The relation between the Goal and scope definition steps distinguished in this Guide and
in ISO 14041 (for reasons of presentation the sequence of ISO steps has been adapted).
1.4.2 Inventory analysis
In ISO 14041 (1998E) the (Life Cycle) Inventory analysis phase (‘LCI’) is broken down into the following
operational steps (ISO 14041, clause 6.1, p.8):
- Preparing for data collection;
- Data collection;
- Validation of data;
- Relating data to unit process;
- Relating data to functional unit;
- Allocation and recycling;
- Data aggregation;
- Refining the system boundaries.
In addition to these operational steps the topics ‘limitation of LCI (interpreting LCI results)’ and ‘study
report’ are mentioned in ISO 14041 (1998E).
Based on ISO 14041 (1998E) and taking into account the steps distinguished in Heijungs et al. (1992),
Lindfors et al. (1995a), Curran (1996) and Wenzel et al. (1997), in this Guide we distinguish the following
steps of the Inventory analysis phase:
Part 3: Scientific background 50 May 2001
- [Procedures]; 1
- Economy-environment system boundary;
- Flow diagram (one item of ‘Preparing for data collection’);
- Format and data categories (ISO step ‘Data categories’);
- Data quality;
- Data collection and relating data to unit processes (including ‘Relating data to unit processes’);
- Data validation;
- Cut-off and data estimation (= ‘Initial system boundaries’ and ‘Criteria for initial inclusion of inputs
and outputs’; in ISO 14041 these steps are part of ‘Goal and scope definition’);
- Multifunctionality and allocation (= ‘Allocation and recycling’);
- Calculation method (= ‘Relating data to functional unit’ and ‘Data aggregation’).
The steps listed cover all ISO steps and elements, but they are here grouped and sequenced differently
under slightly different headings. There are a number of reasons for these additions to and deviations
from ISO:
1. As the overall aim of this document is to provide a practical guide for LCA practitioners based on the
ISO Standards, it is important to parallel the actual steps of a real-world LCA process as closely as
possible.
2. The procedural aspects of each LCA phase are treated in a separate ‘Procedures’ section in the
description of each phase, to avoid cluttering up the technical steps.
3. The ISO step ‘Preparing for data collection’ has been split into ‘Flow diagram‘ and ‘Data collection
and relating data to unit processes‘. The description of each unit process, units of measurement,
data retrieval methods, etc. are all part of ‘Data collection and relating data to unit processes‘.
4. The ISO step ‘Relating data to unit processes’ is now part of the ‘Data collection and relating data to
unit processes‘ step, as ‘Relating data to unit processes’ has too little substance to be treated as
an individual step and is inextricably linked with the activity of data collection.
5. ‘Format’ is lacking as a topic in the ISO framework and has been added here as part of the first data
step: ‘Format and data categories‘.
6. Definition of the economy-environment system boundary is a step that is lacking in the ISO
framework and it has therefore been added here.
7. All calculation steps have been brought together under ‘Calculation method‘, but with a distinction
still being made between non-aggregated and aggregated inventory results.
8. Cut-offs are usually introduced because of data deficiency and general time and resource
constraints on data retrieval. It is only after data collection that this problem becomes evident and it
has therefore been put after data collection. As cut-off may often be avoided by data estimaton
techniques such as input-output analysis (see Section 3.8), the name of this step has been
extended to ‘Cut-off and data estimation‘.
9. The step ‘Refining the system boundaries’ is related to the iterative character of LCA execution and,
as argued above, is not elaborated as a separate step here.
10. Issues for Interpretation, reporting and procedures (including critical review) are treated in the same
way as in the Goal and scope definition (see Section 1.4). The ISO topics ‘Limitation of LCI
(interpreting LCI results)’ and ‘Study report’ are not treated in this Guide as separate steps but as
part of the items ‘Issues for Interpretation’ and ‘Reporting’, respectively.
The relation between the steps distinguished in this guide and the steps of ISO 14041 (1998E) is shown
in Figure 1.4.2.1.
 
1 Parallel to the treatment of this subject in the Goal and scope phase, “Procedures” is a separate step in Part
2a - Guide - but not in Part 3 - Scientific background.
Part 3: Scientific background 51 May 2001
Inventory
analysis
Goal and
scope
definition
Inventory
analysis
Initial system
boundaries
Economy -
environment system
boundary
Flow diagram
Procedures
Description of data
categories
Criteria for initial
inclusion of inputs
and outputs
Data quality
requirements
Study report
ISO 14041This Guide
Cut-off and data
estimation
Calculation method
Multifunctionality and
allocation
Preparing for data
collection
Limitation of LCI
Data collection
Validation of data
Relating data to unit
process
Relating data to
functional unit
Allocation and
recycling
Data aggregation
Refining the system
boundaries
Data validation
Data collection and
relating data to unit
processes
Data quality
Format and data
categories
Figure 1.4.2.1: The relation between the Inventory analysis steps distinguished in this Guide and in ISO
14041 (for reasons of presentation the sequence of ISO steps has been adapted).
Part 3: Scientific background 53 May 2001
1.4.3 Impact assessment
ISO 14042 (2000E) distinguishes the following steps In the (Life Cycle) Impact assessment phase
(‘LCIA’):
- Selection of impact categories, category indicators and characterisation models;
- Assignment of LCI results (Classification);
- Calculation of category indicator results (Characterisation);
- Calculating the magnitude of the category indicator results relative to reference information
(Normalisation);
- Grouping;
- Weighting;
- Data quality analysis;
- Limitations of LCIA;
- Comparative assertions disclosed to the public;
- Reporting and critical review.
The ISO framework is summarised in Figure 1.4.3.1.
Mandatory elements
Selection of impact categories, category indicators and characterization models
Assignment of LCI results (classification)
Calculation of category indicator results (characterization)
Category indicator results (LCIA profile)
Optional elements
Calculation of the magnitude of category indicator results relative to reference information (normalization)
Grouping
Weighting
Data quality analysis
LIFE CYCLE IMPACT ASSESSMENT
Figure 1.4.3.1: The ISO elements of the LCIA phase (source: ISO 14042, 2000E).
ISO 14042 distinguishes mandatory and optional elements. The first mandatory element is ‘Selection
and definition of impact categories, category indicators and characterisation models’. In this step impact
categories (e.g. climate change) are identified along with appropriate category indicators (e.g. infrared
radiative forcing) and the model used to derive the characterisation factors, i.e. the quantitative
relationship between the interventions and the indicator, is established. The second mandatory element
is ‘Assignment of LCI results to category indicators (Classification)’. In the final mandatory element,
‘Calculation of category indicator results (Characterisation)’, guidance