Page 144 - Materials Chemistry, Second Edition

128 3 Life Cycle Inventory Analysis

Thus, generic or background data are always based on the specific analysis of
material and energy flows in defined plants. By building meaningful averages the
data is processed to be usable in unit processes of an LCA. If average values cannot
be calculated, carefully selected, representative single values can also be defined as
generic data. In any case a careful inquiry is necessary on whether they are actually
useful for the objective formulated in the LCA under study.
The use of generic data makes sense – even if some specific data were avail-
able – if the origin of a special raw material is not known or if it is not known
in which factory a material or intermediate product was manufactured, and so
on. Even if the information were available by a certain cut-off date it could have
changed or be incomplete the next day, because one producer in the supply
chain would have changed his suppliers or the oil would have another origin.
These considerations are to show the fact that generic data are not a necessary
evil but the only meaningful alternative for ‘background’ data. It is thus aston-
ishing that the Dutch ‘Handbook on Life Cycle Assessment – Operational Guide
to the ISO Standards’ recommends to avoid the use of generic data for detailed
LCAs. 137)
Transports also are mostly calculated with generic data on fuel consumption and
emissions. Distances, mode of transport and moved material, capacity utilisation,
logistics, should on the other hand be specifically dealt with in the foreground (see
Section 3.2.5).
Beside the actual raw materials there is a wide range of mass products, called
commodities, which are bought on the market, if no long-term contracts cause
permanent links of the producer to a few suppliers. Among others, the most
important commodities are the most important metals, plastics, building materials
and base chemicals. The long-term contracts mentioned move the suppliers to
the foreground, whereas in case of rapidly changing suppliers, commodities
and background processes have to be discussed and procured with appropriate
generic data.
Generic data are indispensable for the conduct of LCIs. These data can be
averaged unit process data or results of partial inventories (cradle-to- (factory-)
gate) LCIs, which should be representative for a specific technology or region. The
expression ‘cradle to factory gate’ indicates that these data represent no genuine
LCIs (‘from cradle to grave’) but only a part of the life cycle. Partial LCIs as generic
data are indispensable for a conduct of complete inventories and LCAs.
An approximate match of system boundaries, especially geographical ones, is a
prerequisite for the correct application of generic data and their respective partial
inventories. Raw materials, materials and chemicals sold worldwide should also
exhibit world-mix data for a calculation of averages. Electricity is mostly supplied
by the national grid (exports and imports are nearly balanced). If on the other
hand production occurs somewhere in Europe, (without precise data), a European
average is preferable (Section 3.2.4). The same is true for other large regions.

137) Guin´ ee et al., 2002; Kl¨ opffer, 2002.