148 Introduction to Renewable Biomaterials
Temporal boundaries are also set in the scope definition. Temporal assumptions, or
assumptions relating to time, can have large influences on the results of a study. It is
important to pick a study timeframe that will best capture the impacts of the product
or processes being studied. Impacts occurring in 100 years is a common temporal
boundary for global warming potential (GWP). In a 100-year temporal boundary,
impacts occurring after 100 years would not be calculated and included in the results.
There is an emerging field of dynamic LCA, which can more accurately model emis-
sions through time for product systems lasting over many years (Daystaret al., 2016;
Levasseuret al., 2010). This new method improves LCA temporal consistency that
enables a better determination of the global impacts over a given time period.
Other aspects to be included in the scope are technology types and geographical
regions. Many studies are spatially dependent, and the overall results and conclusions
may not be broadly applied to other regions. Product manufacturing technology can
also be important to the study results. Products or services from older technologies
often have different impacts than the most current technology. For this reason, it is
important to clearly communicate the type and stage of the technology under analysis.
In addition to the aspect listed, allocation procedures impact assessment methods used
should be reported in the scope of an LCA.
5.3.1.3 Functional Unit
A functional unit is the primary measure of the product, service, or good you are
studying. ISO states “the functional unit defines the quantification of the identified
functions (performance characteristics) of the product. The primary purpose of a
functional unit is to provide a reference to which the inputs and outputs are related.
This reference is necessary to ensure comparability of LCA results” (ISO 14044, 2006).
This can be a service, mass of material, or an amount of energy. Selecting appropriate
functional units is critical to creating an unbiased analysis. For example, comparing
paper milk cartons to glass milk bottles may not be the best option due to the different
possible sizes of each container. The real purpose of the container would be to deliver a
quantity of fresh milk to a consumer. For this example, a better functional unit may be
impacts of a container delivering 8 ounces of milk to a consumer. The results will then
be normalized to a quantity of milk, which is what the consumer really wants not the
container it comes from.
5.3.1.4 Cutoff Criteria
Data collection for an LCA is the most time-intensive and laborious step. To expedite
this process, cutoff criteria are often used. A cutoff criteria defines a level of product
content or other parameter which the study will not consider. For example, material
contents less than 1% of the total product mass are often not considered in the
LCA. This allows the LCA practitioner to focus on data from the main flows while
systematically eliminating flows that may not influence the results. An LCA practitioner
should perform cutoff decisions carefully as some materials can produce emissions and
environmental impacts disproportionate to their component weight.
5.3.1.5 Problems Set – Goal and Scope Definition
Problem 1 Design a goal and scope for a life-cycle analysis that compares two
heating methods to produce steam in a factory: a wood pellet burning furnace versus
a conventional heating oil furnace.
