Page 48 - Materials Chemistry, Second Edition

32 2 Goal and Scope Definition

System boundary
Energy supply
Inputs Outputs
Raw material extraction
Sewage water

Production, processing, formulation Exhaust gas
Energy
Solid waste
Distribution/transport
Raw material Other emissions

Use, re-use, maintenance Products
Other
Recycling

Waste management

Figure 2.4 System boundary of the inventory modified according to Society of Environmen-
tal Toxicology and Chemistry (SETAC) (1991).

infrastructure and so on, contributing less than 1% related to the entire life cycle is
usually without problems. 11) In any case, an error estimation is required.
The cut-off criterion ‘environmental relevance’ is to prevent, for example, the
omission of highly toxic emissions (say polychlorinated dibenzodioxins) in the
investigated product systems due to too small masses.
The primarily highly interlaced systems of the complete system analysis become
one-dimensional approximations by cutting off links. Interlaced subsystems (loops)
are either calculated iteratively or by other suitable mathematical tools. 12) Branches
without feedback represent no deviation of the linear sequence; they may, however,
represent allocation problems (see Section 3.3).

2.2.2.2 Demarcation towards System Surrounding
The system surrounding 13) is composed by the ecosphere (‘environment’; see
Section 2.2.2.1, ‘all that is not technosphere’) plus the large remainder of the
technosphere not included in the analysis. In Figure 2.4, this boundary is called 14)
system boundary. The system under examination receives input from the system
surrounding and delivers output to it.

11) Hunt, Sellers and Franklin (1992).
12) Heijungs and Frischknecht (1998) and Heijungs and Suh (2002).
13) The system surrounding is often called ‘system environment’, which can be misleading.
14) Society of Environmental Toxicology and Chemistry (SETAC) (1991).