Page 69 - Materials Chemistry, Second Edition

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Prime Prime
Material Material Manufacture Distribution Disposal
Extraction Transport

CRADLE GATE 1 GATE 2 GATE 3 GATE 4 GRAVE

FIGURE 2.2 Product life-cycle span steps.

2.3.3.1 Life-Cycle Boundaries

Let us assume that the life-cycle span of a product is composed of the steps shown
in Figure 2.2. Different system boundaries can be defined according to the life-cycle
step; if it is considered the entire life from the prime material extraction until the
final disposal, the limits will be defined as “cradle to grave.” When the destination
of a product is not known, the analysis will be stopped after manufacture and the
limits will be cradle to gate 3. Other studies regarding product “stewardship” will
take care of the product from manufacture until disposal, defining gate 3 to grave.
In a situation of mature LCA practices, each life-cycle step will carry out its own
gate-to-gate analysis and the entire cradle-to-grave process will be the result of the
composition of a set of gate-to-gate systems.

2.3.3.2 Geographic Boundaries
These boundaries consider geographic limits to establish the limits of product sys-
tem. They can be considered life-cycle boundaries when the different life-cycle steps
are confined in some region. These criteria are well recommended in cases of site-
specific studies of LCA, as will be discussed later.

2.3.3.3 Environmental Load Boundaries
Different types of environmental load are renewable and nonrenewable raw materi-
als, air and liquid emissions, solid waste, energy losses, radiation and noise. LCA
can be carried out considering the entire list of inputs and outputs (complete LCA)
or taking into account air and liquid emissions (partial LCA). In Figure 2.3, partial
LCA 1 considers only air and liquid emissions and is carried out from the beginning
(cradle) until gate 2. Partial LCA 2 takes into account only solid waste and energy
losses and goes from gate 1 to the end of life (grave).

2.3.4 DATA REQUIREMENTS
The quality of data used in the life-cycle inventory is naturally reflected in the quality
of the final result of LCA. In this frame, it is important that the data quality be

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