Page 68 - Materials Chemistry, Second Edition

L1644_C02.fm Page 45 Tuesday, October 21, 2003 3:07 PM

TABLE 2.1
Examples of Functional Units
Class of products, process
and services System function Functional unit
Goods use Light generation kWh/day
Laundry washing 5 kg washed clothes
Process Gasoline production m produced/h
3
Liquid effluents treatment t of removed COD/day
Transportation Goods transport tkm*
Passengers transferring Person km

* 100 kg transported 1 km.

Orange juice provides another good example. When the function of the system
under study is orange juice consumption, the production of orange juice, its transport,
processing, packaging, distribution, storage, sewage treatment and final disposal are
considered. If the aim is to compare two different processes of juice production, 1
or 1000 L of orange juice will serve as the functional unit, taking into account that
only the manufacturing system presents different alternatives. However, if the aim
was to compare the use of different types of packaging systems, the functional unit
should be consumption from a 1-L orange juice container.
Flowers are a classic example because people usually want “a bunch of flowers,”
rather than “750 g of flowers” or “flowers for 1 week.” Thus, the functional unit
should be defined as accurately as possible, considering that it should comprise the
selected products and their end use, and that it is compatible with the nature of the
application.
Finally, in practice, the functional unit must be measurable and, when two
products with different life spans are compared, e.g., a match and a lighter, it is
important that the period of use be considered for its establishment.

2.3.3 THE SYSTEM BOUNDARIES
When the goal and scope definition of an LCA is made, it is crucial to define the
system boundaries. They define the range of the system under study and determine
the processes and operations it comprises, such as prime material extraction, man-
ufacturing and waste disposal. In this substep, the inputs and outputs to be taken
into account during the LCA study must be established. According to Lindfors et
al. (1995), these can be the overall input to production as well as input to a single
process; the same is true for output. Even for a quite subjective operation, the
definition of system boundaries can be carried out according to the following
criteria: life-cycle boundaries, geographical boundaries, and environmental load
boundaries.

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