Page 41 - Materials Chemistry, Second Edition

22 LIFE CYCLE ASSESSMENT HANDBOOK

Within ISO, a preferred order for solving the multi-functionality problem
has been designed. It distinguishes several solutions (dividing the unit process
into two or more sub-processes, expanding the system to include the addi-
tional functions, partitioning on the basis of a physical parameter, partitioning
on the basis of an economic parameter), separated by clauses like "wherever
possible" and "where ... cannot be established." This stepwise procedure is a
clear comprise, and in practice leaves so much freedom that LCA studies that
are according to the ISO standard can give conflicting results. One peculiarity
deserves to be mentioned: besides the ISO-based "expanding the system to
include the additional functions," we often see a method that is best described
as "subtracting the avoided impacts from additional functions," but that is
more commonly known as the substitution method or the avoided burdens
method. For instance, when a waste treatment activity co-produces electricity,
the emissions from the regular way of producing the same amount of electric-
ity are subtracted. This method has similarities with that of system expansion,
but of course they are not identical. Many LCA studies employing the substi-
tution method claim to be ISO-compliant, even though strictly speaking ISO
14044 does not mention this method, let alone recommend it. That does not
necessarily mean that these studies are incorrect, of course. Compliance with
ISO is not a sufficient quality guarantee, but also not a necessary one.
After appropriate cut-off and allocation steps, the final inventory results can
be calculated. Typically, this is a table with the quantified inputs from and
outputs to the environment, for each of the alternative systems considered,
expressed in relation to the functional unit. With the present-day software and
databases, this inventory table may be 1000 lines or longer. It contains not only
the familiar pollutants and resources, such as C0 2 , ΝΟ χ, and crude oil, but also
more exotic items, such as 1-pentanol, cyprodinil, and dolomite.

2.1.3 Impact Assessment

Life cycle impact assessment (LCIA), or impact assessment for short, is the
"phase of life cycle assessment aimed at understanding and evaluating the
magnitude and significance of the potential environmental impacts for a prod-
uct system throughout the life cycle of the product." Its motivation comes from
two observations:

• The final result of the inventory analysis, the inventory table, is
too long (e.g., 1000 different items) to handle;
• The inventory table contains many items that require expert
knowledge (such as 2-methyl-2-butene) to understand in terms
of importance.

Impact assessment, and in particular the characterization step, solves both
issues: it "involves the conversion of LCI results to common units and the
aggregation of the converted results within the same impact category."