Page 37 - Materials Chemistry, Second Edition

Life Cycle Assessment: Principles, Practice and Prospects
24
There is also an area of LCA practice where the scope is expanded beyond the traditional func-
tional unit approach to include social and/or economic indicators. There is no clear boundary or
point at which such studies cease to be called LCA and become part of ‘integrated assessments’.
Two other distinctions need to be made in describing LCA practice. The first is between
‘bottom-up’ process analysis studies (see Section 3.3) and ‘top-down’ input-output studies
(and a continuum of hybrid approaches in-between). The second distinction is between conse-
quential and attributional approaches to LCA modelling, which is similar to the distinction in
economics between average and marginal costing. Attributional LCA focuses on development
of average impacts for a supply of commodities and production processes and is historically
how most LCAs have been conducted. Consequential LCA considers the impacts of decisions
(i.e. the net environmental impact from marginal changes in production and consumption). It
takes account of issues of scale, location and market conditions to predict which parts of supply
chains will increase or decrease with changes in demand (Ekval and Weidema 2004).

3.2 The generic elements of LCA
Within the broad category of LCA practice, certain key elements, are always required, and
these are described in this section.
3.2.1 Functional unit
The basis for LCA is the calculation of environmental impacts for the delivery of specific func-
tions or utilities. Conventionally, the functional unit should be the same for all options analysed.
The defining of appropriate functional units is a challenge in LCA primarily because options
may have secondary functions that need to be balanced. The concept of the functional unit has
been expanded by some practitioners to include the economic values of the options analysed.
Conceptually, the functional unit is defined so that results from the LCA can be used to
promote a substitution of the option(s) with lower environmental load for the option(s) with
greater environmental load. With this in mind, the functions need to be so close to equal that
a ‘rational economic person’ (or perhaps a ‘rational environmental person’) would consider
the utility or benefit of each option to be similar. In this way, for example, if different vehicle
options were manufactured using different materials, most people would not consider this a
barrier to purchase. However, if the vehicle options differed in their durability, efficiency,
carrying capacity, speed, range, cost or style, the potential for product substitution would be
limited and the uptake would require some sacrifice or trade-off between different options
and the environment. Of course, there are many instances in which people are willing to make
such trade-offs and where all options have positive and negative features (or functionalities)
needing to be resolved by the decision-maker.

3.2.2 System boundary
Whether practitioners recognise it or not, all LCA studies analyse some form of interconnected
system. If there is a system being analysed, then there must be boundaries to that system.
Normally, the system boundary is conceptually framed in terms of the life cycle stages included
in the study. For example, a study may include all material inputs to the process but exclude
capital equipment, infrastructure and services. Alternatively, the system may be described lit-
erally through a description of all the processes within the boundaries. However, as LCA can
include thousands of unit processes, this is often not practical. Boundaries can be as tight as
the limits of a single unit process, such as the burning of gas extracted from nature, or as broad
as the consumption of goods and services by whole populations.

100804•Life Cycle Assessment 5pp.indd 24 17/02/09 12:46:15 PM