Page 88 - Materials Chemistry, Second Edition

70 LIFE CYCLE ASSESSMENT HANDBOOK

The overarching purpose of LCIA is to provide additional information to
help assess a product system's LCI results to better understand their environ-
mental significance. In other words the LCIA step is intended to be a way to
evaluate the significance of the environmental interventions of an LCI and
support its interpretation within the given project scope. It is, therefore, not the
primary purpose of LCIA to calculate an absolute value of an environmental
indicator or a set of environmental indicators, but it is to determine the relative
importance of each elementary flow within a given environmental problem,
i.e. one of multiple impact categories, and aggregate them into a manageable
set of indicators. When interpreting the LCIA results, it is of primary impor-
tance to keep in mind that the absolute values of these LCIA indicators do not
predict absolute or precise environmental impacts due to:

• The relative expression of potential environmental impacts to
a reference unit,
• The integration of environmental data over space and time,
• The inherent uncertainty in modeling environmental impacts,
and
• The fact that some possible environmental impacts may occur in
the future.

The LCIA phase could be compared to converting currency when consoli-
dating the accounting of an international company. In this analogy, the G&S
defines what should be included in the accounting plan, and the LCI step con-
sists of accounting for all incomes and expenses and reporting them in dif-
ferent monetary units. Thus, the LCIA step is the conversion of the different
national currencies into a single currency to be used to consolidate the accounts.
Currency conversion factors are simple deterministic values, but are computed
by sophisticated economic models. Similarly, characterization factors (CFs) are
also deterministic numbers used as multipliers translating inventory flows
into impact scores with common units representing an environmental issue.
However, these numbers are often backed by calculations that use sophisti-
cated natural science based models to reflect environmental mechanisms along
a cause-effect chain starting from the environmental emission to an impact.
According to ISO 14044 the LCIA consists of 3 mandatory elements and
three optional elements (see Figure 4.2). These elements are described below.

4.2.2 Mandatory Elements
Selection of Impact Categories, Category Indicators and Characterization Models. The
first step within the framework of an impact analysis is the selection of impact
categories in connection with defining the goal and scope of the study. The
impact assessment categories should link the potential impacts and effects to
the entities that we aim to protect. The commonly-accepted areas of protection
(AoP) are: