The system boundaries define what parts of the life cycle and which processes belong to the studied system. Therefore, the boundaries separate the analyzed system from the rest of the Technosphere (surrounding economy), as well as the interactions with the ecosphere (the environment). The definition of the system boundaries has a substantial effect on the LCA results because they establish the unit process from which the environmental impacts should be quantified. The system boundaries are represented in a chart that provides an overview of which parts of the analyzed product systems are included, and which are excluded from the study (Hauschild, M.Z., Rosenbaum, R.K. and Olsen 2018). Figure 4.1.7 shows an example of system boundaries definition for a life cycle of a steel sheet used on roads.

Generally, system boundaries are defined concerning the following parameters (Li et al. 2014; Tillman et al. 1994):

• Natural system, which means, the border between the technical system and natural environment;
• Geographical boundaries, which means the area to which the system is limited;
• Time boundaries refer to the time perspective of the study, and, Technical boundaries relate to the activities that are considered in the study or to the life cycle of another product (if several systems share the same process, the environmental load will be shared between them).

Some recommendations about how to select the system boundaries in an LCA can be found in more 4.1.3:

Additional information related to the goal and scope definition step search in more 4.1.4:

Figure 4.1.6 ISO hierarchy for solving multifunctionality presented in a decision tree.

Figure 4.1.7 Example of system boundaries chart defined for the life cycle of a steel sheet used on roads (based on (Hauschild, M.Z., Rosenbaum, R.K. and Olsen 2018)).