LCAs and LCIs
The concept of life cycle assessment (LCA) originated in the late
1960s when it became clear that the only sensible way to examine industrial systems
was to examine their performance, starting with the extraction of raw materials from the
earth and tracing all operations until the final disposal of these materials as wastes
back into the earth (cradle to grave).
There were two reasons for this approach. First, individual component
operations could apparantly be made cleaner and more efficient by simply displacing the
pollution elsewhere, thus the benefits occurring in one location were offset by the
problems generated elsewhere so that there was no overall real improvement. A current
example is the proposal to introduce electric cars into towns: this reduces the pollution
in the towns but displaces it to the pollution arising elsewhere from the power stations
needed to provide the fuel (electricity). The second reason was that traditionally
engineers had concentrated their efforts into making individual unit operations more
efficient, but nobody was looking at the way in which these unit operations were put
together to form an overall production and use sequence. Sometimes, by rearranging the
building blocks, overall systems can be made more efficient.
In the early 1970s, LCAs concentrated mainly on energy and
raw materials but later air emissions, water emissions and solid waste were included in
the calculations. The 1990 SETAC conference in Vermont was the first to analyse LCAs
into three main stages as shown below.
Figure 1. The three main stages of a life-cycle
assessment.
The stages are:
1. Inventory in which the
data describing the system are collected and converted to a standard format to provide a
description of the physical characteristics of the system of interest.
2. Interpretation in which
the physical data from the inventory are related to observable environmental problems.
3. Improvement in which the
system is modified in some way to reduce or ameliorate the observed environmental impacts.
Once improvements have been suggested then the inventory stage is
repeated to see if the expected improvements do in fact occur and also to identify any
adverse side-effects resulting from the changes. By cycling through the three phases shown
in Figure 1, it is hoped to optimise the environmental characteristics of the system.
The interpretation part of LCA is still being developed with the result
that this step is often omitted from a true LCA study: in such cases, what is really being
presented is a life cycle inventory (LCI).
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