Page 118 - Materials Chemistry, Second Edition

8 Scope Definition 103

windows throughout their use stages were excluded from the system of each
window because users are expected to clean the windows, that all have the same
surface area, in the same way, using the same amount of water and detergent. While
this kind of exclusion is allowed for comparisons between systems, it prevents a
proper hotspot analysis because it is unknown how much the omitted processes
contribute to overall environmental impacts.
Third, constructing an LCI model with ideal boundaries is practically impossi-
ble. This is because the number of unit processes actually required to deliver a
reference flow is often, even for simple products, enormous: Typically, unit pro-
cesses require around 5–10 material or energy inputs that each needs to be produced
by a unit process that in itself requires around 5–10 material or energy inputs, etc.
Furthermore, many product systems include examples of infinite loops where one
process A requires input from another process B to deliver an output that is needed
by process B to produce the input to process A. Every step back in a value chain
represents a step back in time and ideal system boundaries would therefore need to
encompass a large part of industrial history, which is not practically possible to
model. Yet, amongst the enormous number of unit processes that should ideally be
included in the system boundaries, only a minority actually have a quantitatively
relevant contribution to the environmental impacts of the studied product system.
For example, the ballpoint pens used by employees at a coal-fired power plant
obviously have an insignificant contribution to the environmental impacts of a unit
of power generation.
Therefore, all LCA studies in practice cut-off some unit processes that are
actually needed (although to a very limited extent) to deliver the reference flow.
This presents a dilemma of the system scoping. You should include within your
system boundaries the processes that matter, i.e. contribute significantly to the
overall impacts from the product system, but how can you determine whether a
process matters before you know what the total impacts are and can relate the
impacts from the process to this number? The solution to this dilemma lies in the
iterative approach to LCA that was introduced in Sect. 6.3 and presented for
inventory modelling in Sect. 9.3. Figure 8.13 shows examples of excluded product
flows.

8.6.3 Completeness Requirements: Quantitative
or Qualitative?

Completeness requirements are understood quantitatively by the ILCD guideline as
the share (%) of a product’s actual environmental impact that a study aims to
capture. From this understanding, completeness requirements would, for example,
be lower for a study that intends to provide an initial screening of hot spots for a
company to familiarise itself with the concept of life cycle thinking (e.g. 70%), than
for a study that intends to provide an environmental product declaration (EPD) for