Page 183 - Materials Chemistry, Second Edition

10 Life Cycle Impact Assessment 169

set of environmental changes, positive or negative, due to an anthropogenic
intervention. Such impacts are studied and assessed using a wide range of quan-
titative and qualitative tools, all with specific aims and goals to inform or enable
more sustainable decisions. In LCA this is an important phase, as it transforms an
elementary flow from the inventory into its potential impacts on the environment.
This is necessary since elementary flows are just quantities emitted or used but not
directly comparable to each other in terms of the importance of their impact. For
example, 1 kg of methane emitted into air does not have the same impact on climate
change as 1 kg of CO 2 , even though their emitted quantities are the same (1 kg)
since methane is a much stronger greenhouse gas (GHG). LCIA characterisation
methods essentially model the environmental mechanism that underlies each of the
impact categories as a cause–effect chain starting from the environmental inter-
vention (emission or physical interaction) all the way to its impact. However, the
results of the LCIA should neither be interpreted as predicted actual environmental
effects nor as predicted exceedance of thresholds or safety margins nor as risks to
the environment or human health. The results of this LCA phase are scores that
represent potential impacts, a concept that is explained further on.
The ISO 14040/14044 standards (ISO 2006a, b) distinguish mandatory and
optional steps for the LCIA phase, which will all be explained further in this
chapter:
Mandatory steps:

• Selection of impact categories, category indicators and characterisation models
(in practice typically done by choosing an already existing LCIA method)
!Which impacts do I need to assess?
• Classification (assigning LCI results to impact categories according to their
known potential effects, i.e. in practice typically done automatically by LCI
databases and LCA software)
!Which impact(s) does each LCI result contribute to?
• Characterisation (calculating category indicator results quantifying contributions
from the inventory flows to the different impact categories, i.e. typically done
automatically by LCA software)
!How much does each LCI result contribute?

Optional steps:
• Normalisation (expressing LCIA results relative to those of a reference system)
!Is that much?
• Weighting (prioritising or assigning weights to the each impact category)
!Is it important?
• Grouping (aggregating several impact indicator results into a group)
As already mentioned, it is important to keep in mind that the impacts that are
assessed in the LCIA phase should be interpreted as impact potentials, not as actual
impacts, nor as exceeding of thresholds or safety margins, or risk, because they are: