Page 115 - Materials Chemistry, Second Edition

100 A. Bjørn et al.

8.6 System Boundaries and Completeness Requirements

System boundaries demarcate the boundaries between the studied product system
and (1) the surrounding economy (technosphere) and (2) the environment (eco-
sphere). “Completeness requirements” is a related concept that can be used to
determine what processes should be included within the system boundaries to reach
the degree of completeness in the product system modelling that is needed to be in
agreement with the goal of a study (see details below). The setting of the system
boundaries can have a large influence on LCA results because they determine the
unit processes from which environmental impacts should be quantified. At this
point in the scope definition, the system boundaries should be represented in a
diagram that provides an overview of which parts of the studied product system(s)
that are included and which are excluded. An appropriate level of detail in this
diagram is the life cycle stages (such as production, manufacturing, transportation,
retail, use and disposal) or the main processing steps. It is often useful to start with
the process or life cycle stage that delivers the reference flow and then expand
upstream and downstream. See Fig. 8.10 for an example diagram for the study of a
steel sheet used to prevent accidents during roadworks. Note that the diagram does
not need to contain individual unit processes, as this full level of detail will only be
achieved in the actual construction of the inventory model (Chap. 9).

(a)
Extraction and production Manufacturing Use Disposal
of materials
Landfilling
Extraction of Pig iron Crude steel Steel rolling Use on road
iron ore production production Collection
for recycling

System boundaries
(b)

Fig. 8.10 a Example of system boundaries diagram for the life cycle of a steel sheet used to
prevent accidents during roadworks. Only the main process steps in the life cycle are shown.
b Illustration of steel sheets in use