ISO system expansion = substitution

When systems have more than one product, the ISO standards on LCA recommends avoiding partitioning/allocation of the system by instead “expanding the product system to include the additional functions related to the co-products” (ISO 14044, clause

I am sometimes asked: “Is this ‘system expansion’ of ISO not something different from the ‘substitution’ approach (also sometimes described as the ‘avoided burden’ approach) used in consequential LCA?” This lack of clarity in the ISO standards is also sometimes lamented in the literature, e.g. by Brander & Wylie (2011).

This makes me miss the very clear Figure B.2 that we had in the original ISO 14041:1998 (which was merged with ISO 14042 and 14043 into the current ISO 14044 in 2006). This figure illustrated clearly that the authors of the ISO 14040 series viewed system expansion as a substitution. Unfortunately, the informative annex in which this Figure B.2 was placed did not survive the merger. Since few nowadays have direct access to the original ISO 14041 text, let me share this with you:

EXAMPLE 3: Utilizing the energy from waste incineration.

One of the widely used examples of avoiding allocation by expanding the system boundaries is when utilizing the energy output from waste incineration as an input to another product system.

The allocation problem arises because the investigated product system has two outputs: the product or service investigated (A) and the energy output from incineration (B). This allocation problem is often solved by expanding the system boundaries, as illustrated in Figure B.2.

Figure B2-redrawn from ISO1401
Figure B.2 – Expanding system boundaries for waste incineration

End of quote from ISO 14041:1998

As you can see clearly from the figure, the expansion is done by subtracting the alternative system. Mathematically, subtraction is the same as a negative addition. There are also additional examples of this in Figure 15 and 16 in ISO 14049 (entitled “Illustrative examples on how to apply ISO 14044 to goal and scope definition and inventory analysis”).

But the fact that this discussion pops-up from time to time just goes to show the current ISO 14040/44 sometimes fail us in its role as a standard, that is, to minimize or eliminate unnecessary variation (more about that in Weidema 2014).

Brander M, Wylie C. (2011). The use of substitution in attributional life cycle assessment. Greenhouse Gas Measurement and Management 1(3-4):161-166.

Weidema B P (2014). Has ISO 14040/44 failed its role as a standard for LCA? Journal of Industrial Ecology 18(3):324 326