BackPage Primer from Environmental Building News
June 1, 2008
Life-Cycle Assessment:
Tracing a Product's Impacts
If you wanted to know about all the environmental impacts of a product, common sense suggests that you would have to trace that product from the origins of its raw materials, through its manufacture and use, and finally to its fate at the end of its useful life. That’s the premise behind environmental life-cycle assessment (LCA)—a science that aims to quantify all the impacts of a product or service. LCA is often used by manufacturers to compare alternative ingredients and processes for making a product, and by policymakers for establishing preferences for one product over another. When the Coca-Cola Company evaluated whether to switch from glass to plastic soda bottles in the 1970s, its consultants pioneered the use of LCA. (LCA is not the same as life-cycle costing, which looks only at the financial cost of buying, using, and disposing of a product.)
The basic concept is simple, but LCA isn’t easy to do well. First, LCA practitioners have to divide the life cycle of a product into discrete steps so they can measure or estimate the inputs and outputs of each step. Inputs typically consist of raw materials, energy, and water, and outputs include the product itself along with any byproducts and waste products in the form of solid waste, air emissions, and water pollutants. The inputs and outputs of all the steps are combined into a life-cycle inventory that lists every relevant substance and how much of it was consumed or released.
This inventory itemizes inputs and outputs, but it doesn’t tell you what environmental impacts result. That comes with the life-cycle impact assessment, which draws from available scientific research to link each item, such as tons of carbon dioxide released, to an environmental impact category, such as climate change. Some of these links are straightforward, but others depend on many estimates and assumptions. To estimate how many lives (or life-years) will be lost due to the release of a certain carcinogenic chemical, for example, researchers have to make assumptions about how many people will be exposed to that chemical and how it might enter their bodies. Detailed databases and software tools have many of these assumptions built in. These tools simplify the work of LCA practitioners as well as those using LCA research, though it is helpful to know enough about those assumptions to understand what they mean for the reliability and comparability of the results. In general, LCA is useful for impact categories that are easy to quantify, such as fossil fuel depletion, but it tends to ignore or oversimplify those that are not, such as habitat impacts from cutting trees in a forest.
The life-cycle impact assessment yields a score for a product in each impact category. That doesn’t solve the problem of how to compare two products if one looks better in some categories while the other looks better in others. To answer that question, someone has to decide how much importance, or weight, to give each category. Researchers often shy away from doing that, but some LCA tools provide a way for users to input their own, or select preset, value judgments and see the results.
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One of the documents I use to evaluate a products sustainability is ISO 14040 / 14044, ANSI and Smart Building Product Standards prepared by the Institute for Market Transformation to Sustainability.
LCA is the compilation and evaluation of the inputs, outputs and potential enviromental impacts of a product system throughout its life cycle. The primary coversion process is esential to evaluate within the manufacturing process. Each of the standards mentioned are coming together to provide an equal process of review. Credability in certifying compliance standards is what the public needs as well as thrid party evaluators.