Performing a Life-Cycle Assessment


According to the ISO standards governing LCA (ISO 14040:2006 and ISO 14044:2006), the LCA comprises four stages: (1) goal and scope, (2) inventory analysis, (3) impact assessment, and (4) interpretation (Figure 8.2). Completing each stage is not always linear, but it is possible to return to earlier stages, thus forming the iterative nature of LCA.

Goal and Scope

The goal and scope of the LCA define the investigation. For example, the following questions may arise during the stage: Are the goals of the study to perform a strength and weakness analysis, product comparison, product improvement, or eco-labelling? Or, is the question simply to determine the environmental impact of something?

The first step in the goal and scope stage is to define a functional unit (FU). This is a numerical definition of the product/process/service under investigation, e.g., the production of 1 ton of paper. The FU is often extremely


Phases of the LCA. (Modified from ISO 14040: 2006.) specific as this defines most of what is to follow in the study. For example, instead of saying: "driving 100 km in a passenger car", it may be better to state it as: "driving 100 km in an Acme Model X passenger car at a constant speed of 60 km/hr, without passengers". However, the FU may depend on the level of detail required in the study.

Another aspect of the goal and scope is to define the system boundaries, and what parts of the process to include. The LCA could be a cradle-to-gate (everything) assessment, or, if there is a valid reason not to include aspects of the process, cradle-to-gate (excluding recycling), or gate-to-gate (excluding certain inputs and recycling). In determining the overall system boundary under investigation, and the FU chosen, the included aspects are determined. Typically, the boundaries include as much of the process as possible (raw material processing, manufacturing, transportation, electricity production, warehousing, use, and recycling), but this may not be possible, or the information on a certain aspect may simply be missing.

When looking at life cycles of large processes, multiple products may result, e.g., in a petroleum refinery. If the primary product of interest (and the FU) is unclear or difficult to split across the entire process (e.g., petrol, diesel, or LPG which all come from the same production facility), it may be necessary to apply allocation or division of multiple products. This is made possible by mass, economic, or any other basis. This means that instead of placing a quantitative burden on a single FU, the study splits the quantitative burden proportionally across the various products. For example, if a petroleum refinery produces 40% liquid products versus 60% gaseous products, then if one wants the LCA of the liquid products, the boundary may include the entire facility. However, the LCA will only attribute 40% of the result to the liquid products.

In the real world, processes are complex, such that adding recycling and disposal steps can complicate the allocation of the original FU and system boundary decisions further. For example, should products, sub-products, and materials recycled back to the same process, or used as raw materials in another process (where they may be replacing a less environmentally friendly process), be included in the boundaries or not (Figure 8.3)?

< Prev   CONTENTS   Source   Next >