Page 126 - Materials Chemistry, Second Edition

8 Scope Definition 111

steel that is stainless and heat resistant as material input, then it is incompatible with
the product of a unit process producing basic grade steel without these properties.
The scope definition should therefore contain a list of technologies that are
known to be involved in the foreground system and in those parts of the back-
ground system for which such knowledge exists (typically energysupply, waste
management and transportation), specifying representativeness requirements. This
list should be partly based on the outcome of the geographical scope and time
frames in terms of where and when processes are taking place.

8.8 Preparing the Basis for the Impact Assessment

The planning of the impact assessment in the scope definition has two main pur-
poses. The first is to ensure that it is done in accordance with the goal definition and
the second is to prepare for the inventory analysis where the elementary flows
(resources and emissions) that should be included depend on the impact categories
to be covered in the LCIA. These elementary flows may also depend on the par-
ticular LCIA methods that are used to model these impact categories because
different LCIA methods can cover different elementary flows. Planning how to
perform the LCIA prior to the life cycle inventory analysis therefore helps ensuring
that the right data is being collected in the cycle inventory analysis. A brief
guidance on the planning of the LCIA is given in the following sections. Chapter 10
gives a comprehensive introduction to the science behind LCIA and how to report
results.

8.8.1 Selection of Impact Coverage

According to the ISO 14044 standard for LCA, the selection of impact categories to
be covered by an LCA “shall reflect a comprehensive set of environmental issues
related to the product system being studied, taking the goal and scope into con-
sideration”. This means that all environmental impacts where the product system
has relevant contributions must be included in the impact assessment, unless the
goal definition explicitly states otherwise. The latter is the case, e.g. in carbon or
water footprinting studies, and in such studies the limitations imposed by the
narrow impact coverage should be stressed in the goal definition and addressed the
interpretation of results. Other valid reasons to exclude one or more impact cate-
gories from the assessment is when an initial iteration of the LCA shows that they
do not contribute to the differentiation between the alternatives in a comparative
LCA, or when they have a negligible contribution to the overall impacts, estimated
by aggregating indicator scores for different impact categories to a single score
following normalisation and weighting (see Sect. 8.2.5). In this case, the excluded
impact categories must be listed as deliberately omitted in the scope definition of