Page 164 - Materials Chemistry, Second Edition

9 Life Cycle Inventory Analysis 149

9.3.3 Very Low Specificity Data

If efforts to obtain data have been fruitless, one may rely on expert judgement.
People may qualify as experts if they are knowledgeable in the technical domain
relevant for the data (e.g. plastic moulding) or if they have conducted similar LCA
studies themselves in the past. If no expert is available, a last resort is to use a
‘reasonable worst case’ for the calculation of the first iteration of LCA results.
A reasonable worst case value may be derived from knowledge of similar or related
processes or from correlation or calculation from other flows of the process or other
processes. The results will then show if the data is potentially important or negli-
gible (judging against the cut-off criteria identified in the scope definition). In the
first case, the practitioner may try again to obtain data of better quality or address
the issue in the interpretation of results. In the latter case, the reasonable worst case
data may either be kept in the model or removed. Whatever option is chosen it
should be reported (see Sect. 9.7) for the sake of other LCA practitioners wanting to
use (parts of) the inventory model in future LCA studies.

9.4 Constructing and Quality Checking Unit Processes

The data that is collected should represent full operation cycle of the process,
including preparatory activities like heating, calibration (with potential loss of
materials and products as scrap), operation, idling, cleaning and maintenance. It
should also take into account typical scrap rates during operation. This means that
the data collection should be based on a longer period of operation, ideally covering
several production cycles, perhaps one year’s production. Sometimes also the
impacts from the manufacturing and end-of-life stage of the production equipment
are important and then they should also be included in the data collection. When the
data has been collected, it is time to construct unit processes. As mentioned, the
type of data collected can vary (see Table 9.3) and it is important to ensure that all
the data has the right format for a unit process. To reiterate, all data must be in the
form of flows. Elementary flows must be in a unit that matches that of the char-
acterisation factors to be applied (‘kg’ in many cases), and all flows should be
scaled to 1 unit of the reference flow of a unit process (see Figs. 9.6 and 9.7). Note
that unit processes obtained from LCI databases already have the right format and
are therefore ready to incorporate in an LCI model (see Sect. 9.5).

9.4.1 Quality Check of a Unit Process

When constructing unit processes there is a risk that they are incomplete and that
there are errors in the flow quantities. Incompleteness may be caused by the fact that