Background, Aim and Scope:
Allocation methodology for creating life cycle inventories is frequently addressed, yet the practice continues to be in a state of flux. Clearly there are many ways in which allocation can be carried out with no single method providing a general solution. ISO 14041 identifies a methodological framework, although it does not provide specific guidance on when and how to apply the steps that are outlined in the standard. An expansion, or elaboration, of the current ISO framework for allocation is needed.
Main Features:
A literature search was conducted on the various allocation schemes that are used to create life cycle inventories, with a focus on industrial processes. The results are grouped by ‘general guidelines' and ‘industry-specific’ applications.
Results:
The search uncovered procedures that support larger efforts, such as the U.S. Database Project and CML’s Operational Guide. Other researchers looked at industry-specific studies to examine the effect of varying input on the outputs. These studies typically attempt to demonstrate how allocation depends on a system’s operation.
Discussion:
At this time, there is no single, scientifically-based method for input and co-product allocation. The only way to allocate burdens is in the application of assumptions drawn from sound, transparent logic. Therefore, any conclusions that are drawn and any decisions made as a result of how the data are partitioned are themselves subject to the same assumptions.
Conclusions:
A recurring theme is the need to match the methodological choice with the goal of the study. However, guidance remains lacking. While system expansion is the preferred approach and avoids allocation altogether, it leads to a larger, more complicated model that requires more data. Data accessibility, time, and effort become significant and bring the practicality of applying system expansion into question.
Perspectives:
It would be useful to develop the range of allocation approaches aligned with different applications (i.e. goals). These approaches should be tested in various case studies for further discussion within the LCA community. Emphasis in these tests should be on the effect of modelling variations on the decision outcome when analyzing an entire system and not focus at the single process level.
|
