Page 37 - Materials Chemistry, Second Edition

18 LIFE CYCLE ASSESSMENT HANDBOOK

An important aspect of the scope definition is the functional unit. It is obvi-
ously pointless to compare an incandescent light bulb with an LED light bulb:
the life spans and performances differ considerably, and the function is not
having a light bulb, but having light of a certain quality. The functional unit
expresses the function of the products, and, thereby, offers a way to equalize
differences in performance. A functional unit for analyzing lighting systems
could thus better be phrased in terms of the function, for instance "lighting a
standard room of 15 square meters with 1000 lumen for 1 hour." As LCA math-
ematically employs a linear calculation rule, the results will scale by choosing
a numerically different functional unit (say, "lighting a standard room of
20 square meters with 800 lumen for 3 hours"), but the alternatives consid-
ered will scale up or down consistently, so this will not affect the conclusions.
A consequence is, however, that LCA cannot tell if a product is "sustainable"
or "environmentally friendly;" LCA can only indicate if product X is "more
sustainable" or "more environmentally friendly" than product Y, or that the
use phase is the "least sustainable" or "least environmentally friendly" part of
the life cycle for product Z.
The scope definition further sets the main outline on a number of subjects
that are discussed and further refined in more detail in the later phases. These
include, among others:

• system boundaries;
• impact categories;
• treatment of uncertainty.

The ISO standard and some other text in places suggest that these topics
are implemented in detail in the scope definition. This is wrong: the goal and
scope definition is not concerned with collecting data or calculating results, so
no concrete details on such topics can be specified at this phase.

2.1.2 Inventory Analysis

ISO defines life cycle inventory analysis (LCI) as the "phase of life cycle assess-
ment involving the compilation and quantification of inputs and outputs for
a product throughout its life cycle." It will be clear that quantification is an
important aspect here, and numbers, in terms of data and calculations, are of
central concern in the inventory analysis.
The LCI is built on the basis of the unit process. A unit process is the "smallest
element considered in the life cycle inventory analysis for which input and
output data are quantified." Examples of unit process are coal mining, steel
production, refining of oil, production of furniture, use of a television set, recy-
cling of waste paper, and transport by lorry. Each of these processes is described
in quantitative terms as having inputs and outputs. In LCA, a unit process is
treated as a black box that converts a bundle of inputs into a bundle of outputs.
Inputs come in several types: products (including components, materials, and
services), waste for treatment, and natural resources (including fossils, ores,