MP15 Tools / Methods / Applications
Monday, 14 November 2005: 8:00 AM - 6:30 PM in Exhibit Hall

(JOL-1118-439737) Defining LCA System Boundaries Based on Unit Process Specific Cut-offs and on Input-Ouput.

Rebitzer, G.^{1, 2}, Jolliet, O.², ¹ Alcan Technology & Management, Neuhausen am Rheinfall, Switzerland, CH-8212² Ecole Polytechnique Fédérale de Lausanne (EPFL), Lausanne, Switzerland, CH-1015

ABSTRACT- Defining LCA System Boundaries Based on Unit Process Specific Cut-offs and on Input-Ouput In ISO 14041 possibilities for cut-off criteria, i.e. criteria based on which a unit process can be excluded from the product system model, are defined. If a cut-off criterion of e.g. 5% of environmental relevance is chosen, this means that every input flow, whose cradle-to gate production has an impact of less than 5% compared to the functional unit studied, can be omitted. there is one inherent problem with this procedure: The procedure can only be applied, if the complete product system with all unit processes and associated elementary flows is known and can be calculated, which make the criteria of little use operationally. Due to the inherent problems with defining cut-off criteria in relation to the overall system, a much simpler operational definition is proposed here, focusing on the single unit process only and based on the mass of the input and output flows in question. Flows that can only be represented in energy units as well as elementary flows are not submitted to any cut-offs as they are well documented and easy to obtain. The approach is empirically tested using detailed cradle-to-gate LCAs of a number reference flows. For this the result of the detailed LCA is assumed to be 100% and it is tested how results with different process specific cut-offs affect the result for the following materials: plastics PE (HD) and ABS, metals primary aluminum, cast iron, and primary steel as well as glass fibers and paper. Results shows that a cut-off of 4% on mass in unit processes have a very high probability of reaching 80%. Based on this sample, in 92% of all cases, the 4% cut-off is sufficient to cover 80% of the impacts of all midpoint impact categories of the IMPACT 2002+ method. At damage level, the 4% cut-off is sufficient, but for climate change where a 2% cut-off is eventually required. This approach can be complemented by a check of most important processes as identified using Input-Output LCA, enabling to check that all important processes have been well considered.

Key words: LCA, system boundaries, cut-off, Input-Output