Page 72 - Materials Chemistry, Second Edition

54 LIFE CYCLE ASSESSMENT HANDBOOK

• Types and quantities of useful outputs (product of interest,
co-products, recycled scrap, recovered heat, etc.)
• Types and quantities of water inputs (emphasis on consumptive
use of fresh water)
• Types and quantities of solid wastes and disposition of each type
of waste (e.g., landfilled, burned, burned with energy recovery,
land applied, etc.)
• Types and quantities of emissions to air
• Types and quantities of emissions to water
• Types and quantities of materials used to package outgoing
product

For emissions, it is preferable to gather data on process emissions released
to the environment after any on-site controls or treatment have been applied.
If the reported emissions include fuel combustion emissions, it is important
that this be noted, so that fuel-related emissions are not double-counted later
when constructing the life cycle inventory model and linking to data sets for
the reported process fuels.
Emissions should be speciated to the extent possible in order to facilitate
subsequent impact assessment. Instead of reporting a group of emissions as
volatile organic compounds (VOC), the chemical composition of the emissions
should be reported. Different isomers of a chemical can have different human
health and ecotoxicity impacts (e.g., ortho- and para-xylene), so it is desirable
to speciate emissions as precisely as possible.
Cut-Off Criteria. Criteria for excluding components or materials are defined
at the outset of the project but may change based on limitations encountered as
the study is conducted. Cut-off rules are typically expressed in terms of mass,
for example, "the study will account for at least 95% of the total mass of inputs,
and no input shall be excluded that individually contributes 1% or more of the
mass/' Ideally, a life cycle study would account for all life cycle steps and 100%
of the content of product, modeled using data for the actual materials and pro-
cesses. Practically, data are often not available for some processes or materials
or cannot be gathered within the time and budget constraints for the study.
This is often true in comparative analyses where the organization sponsoring
the study can provide detailed data on their own system, but alternative sys-
tems must be modeled using publicly available data.
Before deciding to exclude materials or processes from the study, it is impor-
tant to carefully consider the potential effect on study results. Mass contribu-
tion is usually the criterion used to identify components for possible exclusion,
but a material with a small mass contribution may have significant impacts on
energy or environmental impacts. For example, an exterior metal plating a few
microns thick may add only a tiny amount to the mass of a product. However,
the energy and emissions associated with the production of the metal, or metal
emissions from the plating process, may have impacts that are large relative to
the mass of material used in the product.
Another example would be a thin exterior coating that is cured in an energy-
intensive baking process. Even if data on production of the specific coating