Page 78 - Materials Chemistry, Second Edition

6 Introduction to LCA Methodology 63
3. Characterisation using environmental models for the impact category to
quantify the ability of each of the assigned elementary flows to impact the
indicator of the category. The resulting characterised impact scores are
expressed in a common metric for the impact category. This allows aggregation
of all contributions into one score, representing the total impact that the product
system has for that category. The collection of aggregated indicator scores for
the different impact categories (each expressed in its own metric) constitutes the
characterised impact profile of the product system.
4. Normalisation is used to inform about the relative magnitude of each of the
characterised scores for the different impact categories by expressing them
relative to a common set of reference impacts—one reference impact per impact
category. Often the background impact from society is used as a reference. The
result of the normalisation is the normalised impact profile of the product system
in which all category indicator scores are expressed in the same metric.
5. Grouping or weighting supports comparison across the impact categories by
grouping and possibly ranking them according to their perceived severity, or by
weighting them using weighting factors that for each impact category gives a
quantitative expression of how severe it is relative to the other impact categories.
Quantitative weighting allows aggregation of all the weighted impact scores into
one overall environmental impact score for the product system, which may be
useful when the results of the LCA are used in decision support together with
other condensed information like the economic costs of the alternatives.
The main focus of this book is the traditional environmental LCA focusing on
the environmental impacts of the product system, but for sustainability assessment,
also social and economic impacts need to be considered. For these other dimensions
of sustainability, a life cycle perspective is as relevant as it is for the environmental
dimension and in a life cycle sustainability assessment (LCSA—See Chap. 5) they
may be addressed through a social LCA (S-LCA) and a life cycle costing analysis
(LCC). Both of these assessment techniques have their own distinct methodological
foundation which shares the fundamental framework of environmental LCA but has
many distinct elements in all phases of the methodology as introduced in Chaps. 15
(LCC) and 16 (S-LCA).

Interpretation The results of the study are interpreted in order to answer the
question(s) posed as part of the goal definition (see Chap. 12). The interpretation
considers both results of the inventory analysis and the impact assessment elements
characterisation and, possibly, normalisation and weighting. The interpretation
must be done with the goal and scope definition in mind and respect the restrictions
that the scoping choices impose on a meaningful interpretation of the results, e.g.
due to geographical, temporal or technological assumptions.
Sensitivity analysis and uncertainty analysis are applied as part of the inter-
pretation to guide the development of conclusions from the results, to appraise the
robustness of the conclusions, and to identify the focus points for further work in
order to further strengthen the conslusions.