Page 39 - Materials Chemistry, Second Edition

Life Cycle Assessment: Principles, Practice and Prospects
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ISO 14040 Standards (Guinee et al. 2001)). The following is a brief description, included here
to indicate the general approach for process LCA.
The first stage is to decide on the appropriate question. Referred to as ‘goal and scope’ in the
standards, the question asked in an LCA may be self-evident, but often requires careful consid-
eration. The many different environmental issues and preconceptions that the people who have
commissioned the LCA or the practitioners bring to the study can obscure important issues
around identification of the appropriate question. Also, an initially clear question may prove to
be inappropriate or inadequate, and the underlying question of the study may shift accordingly.
It is essential to plan activities and resources carefully, since data requirements often
dominate the work involved in conducting an LCA. The system boundaries of the LCA need to
be identified carefully, considering the implications of these boundaries for resources and data
collection, the types of data to be collected, and the impacts to be assessed in the study. This
may involve analysis of pre-existing LCAs of the same or similar products or different but
relevant products. It may also involve conducting a small streamlined LCA (see Section 3.4) to
refine the scope and identify important issues in the LCA. A process tree describing the proc-
esses inside the system boundary is also useful in the planning of the LCA.
The second stage commences with building a mathematical model of the production
system. This can be as simple as a Microsoft Excel spreadsheet adding emission factors (emis-
sions per unit of production) to the requirements for a product system. Alternatively, LCA
software can be used to link thousands of processes, or a variety of hybrid approaches can be
adopted. LCA modelling can be separated into the foreground system and the background
system. The foreground system includes the processes that are investigated in detail. The back-
ground system includes data taken from pre-existing information, which is used in the calcu-
lation, but is not a focal point of the investigation.
A life cycle inventory for the study can then be produced. Essentially, this is a list of all
resource uses and emissions that occur due to the use of materials and activities needed to
deliver all options under consideration. Once this inventory is complete, the third stage involv-
ing assessment of impacts arising from these uses and emissions can be undertaken, according
to the goal and scope. Assessment is typically undertaken for a set of impact indicators. These
are calculated in the third stage of the LCA, usually with pre-existing factors (characterisation
factors) that group resource inputs and emissions into the indicators. The number of indica-
tors typically varies from 1 to 10 in most LCAs. Where there are more than 10 indicators,
drawing conclusions can become complex, and this illustrates the nature of environmental
impact assessment generally as one fraught with ‘wicked’ (complex) problems of relative
weighting and subjective values regarding diverse and various impacts.
The fourth stage involves results interpretation. Having calculated impact indicators, LCA
results should be validated in some way, and at minimum this should include a ‘reality check’
against expected outcomes to identify any obvious data or modelling errors. Once the general
integrity of the model has been verified, results can be interrogated to identify sensitivities,
major contributing factors and, in comparative studies, the key differences between the
options. Once this has been achieved, alternative options may be considered, the functional
unit may be varied, and extensions to the study may be undertaken.
Most LCAs use process analysis. Classic examples examined elsewhere in this book are the
LCAs on waste and recycling (see Chapter 6), LCAs on water management (see Chapter 8) and
the biofuels LCAs (see Chapter 10).

3.4 Streamlined LCA
Streamlined LCA encompasses a group of approaches designed to simplify and reduce the
time, cost and effort involved in conducting a LCA, while still facilitating accurate and effec-
tive decisions. In a North American survey, LCA practitioners noted that a streamlined LCA:

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