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(1998), the problem of the availability of output data can be avoided in some cases
by carrying out mass and energy balances from some inputs in order to calculate
output values. This can be entirely adequate in many cases, and sometimes, even
better than using data from direct measurements of the releases or emissions.
Finally, all data must be well specified concerning type and amount. Because
the data collected are originally intended for other purposes, they must be processed.
Units must be converted to a standard set, preferably to SI units, and the data
normalized, i.e., expressed in relation to a given output from a stage or operation
comprised by the product system. The previous procedure of data normalization for
each step of the system is helpful and will make the further step of environmental
loads calculation easy.

2.4.3 APPLICATION OF ALLOCATION CRITERIA
In LCA, the term “allocation” means distribution of environmental loads. If we
consider a manufacturing process for only one product, there is no allocation problem
because all the environmental loads must be assigned to that product. In a very
common case in process industries, the same process delivers several products, so
allocation criteria need to be created in order to distribute the environmental load.
For example, considering the production of eggs on a chicken farm, we will
have different sizes of eggs to be sold at the market as products at corresponding
prices. The application of the LCI of this farm allows distributing the environmental
load of inputs (animal food, water, electricity) and the ones of the farm itself
(emissions, odors, wastes, etc.) into the eggs’ production, according to some distri-
bution criteria. Instead of considering the distribution based on the number of eggs,
it appears to be more reliable to distribute the environmental load according to the
weight of the eggs. Weight has been used here as an allocation criterion.
Let us now consider the example of the allocation of environmental loads due
to road transport of goods in a truck. If we are dealing with the transport of foam
mattresses of different density, the more appropriate allocation criteria would be in
this case the volume of each mattress, provided the capacity of transport is not
limited by the weight but by the volume.
Another illustration is provided by a detergent industry that sells a detergent in
two different concentrations: standard and concentrated. In this case it is clear that
the allocation criterion to distribute the environmental load would be the weight of
active product (detergent) in each type of commercial product.
It is difficult to define general rules for environmental load allocation because
of the variety of options; sometimes different criteria can be used for the same
process. An extended treatment of allocation criteria can be found in SETAC (1993),
Pedersen (1993) and Ekvall and Finnveden (2001). Nevertheless, some indicative
rules can be used:

1. The observed product bears the entire EL.
2. EL is divided proportionally to the weight of the product.
3. EL is divided proportionally to the energy content of the product.

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