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LCA part3

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generic guidelines, which need to be elaborated further in each LCA study, on how to simplify certain
methodological elements.
Part 3: Scientific background 75 May 2001
- Temporal boundaries for impacts should be given and justified.
- The final choice of impact categories, level of assessment and omitted categories and flows shall be
reported according to the classification list given in this guideline [in this Guide, see Section 4.2].
- Maximum base-line data quality requirements should be justified.
- Any deviation from initial plans may be reported.
- Any other limitations or assumptions of relevance to the results of the study shall be reported.
Meier et al., 1997 give the following reporting guidelines for the scope phase:
- The boundaries, methodology, data categories and assumptions should be clearly stated and under-
standable. The scope of the study should be defined in sufficient detail to enable the study to
address the stated objectives including stages of the life cycle, system boundaries, methodology,
data requirements and assumptions.
- Data quality goals and any variability of data considered in the study should be clearly established
and detailed.
- The methodology used should be clearly and transparently stated and any differences in
methodology from a full LCA should be explained. All assumptions and value judgements should be
clearly detailed along with the justification for the assumptions.
These authors also provide these reporting guidelines in the form of a practitioner’s checklist.
PROSPECTS
The discussion on descriptive and change-oriented (retrospective – prospective) analysis is still
continuing and it is expected that this will give rise to new ideas in the nearer and more distant future.
No specific developments are foreseen in the other areas.
CONCLUSIONS
Two elements can be distinguished with respect to the Scope of the study:
1. the main characteristics of the study, including temporal, geographical and technology coverage,
coverage of economic processes, coverage of environmental interventions and impact categories,
mode of analysis and level of sophistication of the study; and
2. reporting, resulting in a Goal and Scope Report.
The step Scope definition deals only with the main characteristics of the intended LCA study. Issues to
be covered by a Goal and Scope Report are discussed elsewhere.
With respect to these main characteristics of an LCA the following recommendations are made:
temporal coverage
specify base year or period according to ISO 14041
geographical coverage
specify geographical area according to ISO 14041
technology coverage
specify technology coverage according to ISO 14041; take current state-of-the-art technology as the
baseline
coverage of economic processes
include all economic processes; narrow the number of economic processes included in cradle-to-gate,
gate-to-gate or a difference analysis
coverage of environmental interventions and impact categories
include all impact categories for which practical methods are available and all environmental
interventions for which characterisation factors are available, unless the scope is explicitly narrowed to a
few environmental interventions and/or impact categories; include remaining impact categories and
interventions qualitatively as far as possible (‘flags’)
mode of analysis
change-oriented analysis for structural decisions
Part 3: Scientific background 76 May 2001
level of sophistication
distinction between detailed, simplified and options for extensions
RESEARCH RECOMMENDATIONS
No research recommended.
2.4 Function, functional unit, alternatives and reference flows
TOPIC
In this step the function, functional unit, alternatives and reference flows are defined. The functional unit
describes the primary function(s) fulfilled by a (product) system, and indicates how much of this function
is to be considered in the intended LCA study. It will be used as a basis for selecting one or more
alternative (product) systems that might provide these function(s). The functional unit enables different
systems to be treated as functionally equivalent and allows reference flows to be determined for each of
them.
DEVELOPMENTS IN THE LAST DECADE
ISO 14041 (1998E), clause 5.3.2 states the following with regard to the topic of function and functional
unit (see textbox):
Based on these ISO 14041 requirements, the following steps are distinguished in ISO/TR 14049 (1998)
for defining a functional unit and determining the reference flows:
- identification of functions;
- selection of one or more functions as the relevant one(s);
Heijungs et al. (1992)
In Heijungs et al. (1992) this topic was treated under the heading “Defining the subject of the study” (section
1.3 of 1992 Guide). It was stated there that quantitative terms can be included in the process tree once a
functional unit has been selected, implying that quantification of the reference flow was considered to be
part of the Inventory analysis. The selection of the (product) systems to be compared and considered
equivalent on the basis of the functional unit defined, was also an explicit element of the step “Defining the
subject of the study” in Heijungs et al. (1992).
In defining the scope of an LCA study, a clear statement on the specification of the functions (performance
characteristics) of the product shall be made.
The functional unit defines the quantification of these identified functions. The functional unit shall be
consistent with the goal and scope of the study.
One of the primary purposes of a functional unit is to provide a reference to which the input and output data
can be normalised (in a mathematical sense). Therefore the functional unit shall be clearly defined and
measurable.
Having defined the functional unit, the amount of product, which is necessary to fulfil the function, shall be
quantified. The result of this quantification is the reference flow.
The reference flow is then used to calculate the input and outputs of the system. Comparisons between
systems shall be done on the basis of the same function, quantified by the same functional unit in the form
of their reference flows.
If additional functions of any of the systems are not taken into account in the comparison of functional units,
then these omissions shall be documented. For example, systems A and B perform functions x and y
which are represented by the selected functional unit, but system A also performs function z which is not
represented in the functional unit. It shall then be documented that function z is excluded from this
functional unit. As an alternative, systems associated with the delivery of function z may be added to the
boundary of system B to make the systems more comparable. In these cases, the processes selected
shall be documented and justified.
Source: ISO 14041, 1998E.
Part 3: Scientific background 77 May 2001
- defining the functional unit;
- determining the reference flow.
Below these four steps are described, based largely on ISO/TR 14049 (1998).
Identification of functions
In this step the purpose served by the product system, i.e. its function or functions, is identified. The
starting point for this procedure may be a specific product to be studied (e.g. wall paint) or it may be the
final need or goal, which may sometimes be fulfilled by several distinct products (e.g. wall decoration,
which may be fulfilled by both paint and wallpaper or a combination of these). The functions are related
to specific product (e.g. packaging) or process properties (e.g. transport), each of which may:
- fulfil specific needs and thereby have a use value, which typically creates economic value to the
supplier of the product,
- affect the functioning of other economic systems (e.g. wallpaper may have a - small - insulation
effect, thus affecting the heat requirements of the building).
Selection of function(s)
In this step the relevant functions are selected, on the basis of which a functional unit will be defined and
equivalent (product)