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Figure 3: Process Flow Diagram
A system‟s boundaries are defined by cut-off criteria. Cut-off criteria are used to define the
parts and materials included in and excluded from the product system. For example, cutoff
criteria can be used to determine that any material production process that contributes
less than 5% to the product‟s overall weight can be excluded. Cut-off criteria might also be
based on the number of processing steps in a process chain or the estimated contribution
of a process to the overall environmental impact of the system.
Often a combination of different cut-off criteria has to be used in order to define the
system boundaries properly. For example, when the system boundaries are defined by
cut-off criteria according to mass, an additional check should be carried out to determine
whether or not small but very effective amounts of strong pollutants and toxins are cut off
the system. To avoid that, additional cut-off criteria according to impact can be applied.
There are four main options to define the system boundaries used (shown in Figure 4):
Cradle to Grave: includes the material and energy production chain and all
processes from the raw material extraction through the production, transportation
and use phase up to the product‟s end of life treatment.
Cradle to Gate: includes all processes from the raw material extraction through
the production phase (gate of the factory); used to determine the environmental
impact of the production of a product.
Gate to Grave: includes the processes from the use and end-of-life phases
(everything post production); used to determine the environmental impacts of a
product once it leaves the factory.
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