Understanding environmental impacts and quantifiable measures
In North America, the environmental impacts reported by EPDs are based on a listing of impact categories established by the U. S. Environmental Protection Agency (EPA). This listing, called the Tool for the Reduction and Assessment of Chemical and other Environmental Impacts (TRACI), categorizes a number of key environmental impacts related to the release of various chemicals into the atmosphere, ground, and water. Currently, five of the impacts are included in the data provided by most EPDs.
In addition to these primary environmental impact categories, EPDs also include an analysis of the energy consumed during the product’s lifecycle, and classify this energy into renewable and nonrenewable sources. Further, EPDs include data regarding energy, water, and other resource consumption, as well as information about hazardous and nonhazardous waste generated over the product lifecycle. Figure 1 provides a listing of the typical impact categories and other environmental indicators found in EPDs, along with a brief description of their effects.
All the data reported in an EPD are also quantified to allow for comparison of environmental impacts among similar products. In the case of the five TRACI impact categories, these measures are based on chemical or molecular values that can be added to the impacts of other products to help establish an overall environmental ‘footprint’ for a combination of products, such as a building or major building component. For other environmental indicators, the metrics are based on common measures for energy, volume, or mass. Figure 2 provides a listing of the specific metrics associated with each typical impact category and environmental indicator.
With TRACI impacts, the specific chemical selected is used as a common denominator for similar chemicals yielding a similar result. As an example, although carbon dioxide (CO2) is the most-recognized greenhouse gas, TRACI allows for the conversion of other gasses such as methane (CH4) and ozone (O3) into the equivalent amount of CO2 that would cause the same effect.
Since TRACI measures accommodate the range of chemicals associated with environmental impact, they can be added to the impacts of other products to establish an overall environmental footprint for a whole building constructed from these products. This additive nature of EPD data is very important in the development of calculators such as the Athena Impact Estimator, used to assess the environmental impacts of whole buildings or major sub-systems.
Although the measures used in product declarations are quantifiable, it is important that one recognizes EPDs only provide an estimate or prediction of the magnitude of these impacts. Since lifecycle assessment is a modeling tool, it cannot provide exact values of any impact. However, when conducted in accordance with recognized procedures, it can provide reasonable and comparable values useful for evaluating the overall sustainability of products.