The system boundaries of a product, process or service system need to be specified in terms of several dimensions (Tillman et al. 1994), namely:

• Boundaries in relation to the natural system

• Geographical boundaries

• Time boundaries

• Boundaries within the technical system

In general, activities included in the flow model of a technical system (the inven­tory model) are activities under human control. However, when a flow enters

(or leaves) human control, it also enters (or leaves) the technical system. While it is relatively easy for non-renewable resources such as oil and minerals to be defined in the ‘cradle’, i. e., during the extraction thereof, the boundaries for renewable resources, between the technical and the natural system, are less easy to draw. Renewable resources may be divided into fund resources (e. g. forests and agricultural land) and flowing resources (e. g. solar radiation and fresh water streams). In many cases, the boundary between the technical and the environmental system is obvious. However, when the life cycle includes forestry, agriculture, emissions to external wastewater systems and landfills, the system boundary needs to be explicitly defined (Finnveden et al. 2009).

Assessing bioenergy systems, geographical boundaries are an important con­sideration. Certain types of biomass feedstock may be limited to certain areas, and productivities may differ from area to area because they are limited by the availability of water, climate, soil or terrain conditions. Furthermore, infrastructure such as electricity production, waste management and transport systems may vary between regions (Von Doderer 2012).

Time boundaries, when defining the goal and scope of the study, are an important aspect of the LCA. Time defines the type of LCA study to be used. Change-oriented LCAs are future bound. They look forward in time, since they are about alternative choices of action. Accounting LCAs ask what environmental impact a product may be made responsible for; hence, they are retrospective (Baumann and Tillman 2004).

Boundaries within the technical system relate, to production capital and person­nel. Whether the environmental impact from production and maintenance of capital goods should be included in an LCA has been debated (Baumann and Tillman

2004) . For accounting LCAs, the guiding principle is that the study should be as complete as possible, and the production and maintenance of capital goods should thus be included. For change-oriented LCAs, whether or not capital goods will be affected by change has to be considered. A topic that is similar to that of capital goods is that of personnel. Processes require personnel, and personnel need food, transportation and so on. However personnel-related environmental impacts are usually not included in an LCA (Baumann and Tillman 2004).

Boundaries within the technical system include those in relation to other products’ life cycles. Sometimes several products (or functions) share the same pro — cess(es). If the environmental load of these processes is to be expressed in relation to a single function, then there is an allocation problem. A detailed discussion of the types of allocation problems, the principles pertaining to allocation, and specific operational allocation methods can be found in Baumann and Tillman (2004).