Page 38 - Materials Chemistry, Second Edition

3.2.3 Inputs and outputs Life cycle assessment in practice 25
LCAs are constructed through the calculation of inputs and outputs required, or arising as a
consequence of, the delivery of the functional unit. The inputs and outputs may be technical
processes such as materials, services and processes, elementary flows to and from the environ-
ment such as coal, minerals and land use, and/or inputs and outputs to air, water and soil such
as carbon dioxide, nitrogen and heavy metals. All LCAs have some elementary flows, other-
wise there are no impacts. The number and aggregation of technical flows vary substantially
with the type of LCA and the system being investigated.

3.2.4 Impact assessment
While the type and number of indicators used in LCAs vary, all LCAs should have some indi-
cator, otherwise analysis of impacts is not possible. Some studies claim to consider only a life
cycle inventory and do not include impact assessment, although this normally means that
energy and greenhouse gases are the focus of the study, or that only a very narrow group of
emissions or priority pollutants are considered (e.g. nitrous oxides, sulphur oxides, hydrocar-
bons and carbon dioxide).

3.3 ‘Bottom-up’ process analysis
Bottom-up process analysis refers to process-based modelling that begins at the bottom of the
supply chain and pieces together the individual unit processes that make up a product’s system.
Traditionally, the first stage includes mineral extraction, energy production and the transport
systems invariably required to produce almost anything in modern economies. For agricul-
tural production, the first stage may be field preparation. Unique to bottom-up process analysis
is that data is collected for each of these processes by measurement and modelling of each
process at either local, regional or national levels, although generally the process model will
represent a single process or group of processes analogous to a factory or operation. This is
distinct from economic input-output analysis, where the unit processes are economic sectors.
The unit processes in LCA are connected by virtue of energy and material flows between them.
Hence, coal is used by electricity; electricity is used by timber milling; timber is used to make
buildings, and so on. The circular nature of the economy is represented by the complicating
fact that buildings are used in the extraction of coal.
One characteristic of bottom-up analysis is its focus on major materials and energy flows
and the exclusion of minor and service-oriented inputs. Small material flows may be excluded,
as suggested in the ISO standards, based on their mass energy or environmental significance.
So, for example, where timber framing is used in coal-mining operations, it may be excluded
from coal production as the impact of timber production and the mass of timber used may be
less than 1% of the mass of coal extracted. In this case, timber will be insignificant in environ-
mental terms compared to energy inputs to coal mining and transport of coal. If the LCA
study is expanded so that electricity generation is considered more generally, the relevance of
timber used in coal mining as an input to electricity will become even less significant. Process
analysis is rich in this type of detail.
3.3.1 Process LCA: method and approach
ISO standards (ISO 14040:2006 ‘Environmental management – Life cycle assessment – Princi-
ples and framework’; and ISO 14044:2006 ‘Environmental management – Life cycle assess-
ment – Requirements and guidelines’) provide a sound overview of the LCA process, and there
are many sources of advice on how to undertake LCA accordingly (e.g. ‘the CML guide’ to

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