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4. Environmental loading is divided proportionally to the volume of the
product.
5. In cases in which chemical reactions are involved, the EL is divided
according to a molar or heat reaction basis.
6. Allocation among different types of product ﬂows can be solved by using
avoided environmental loads.
7. Allocation is avoided with the concept of system expansion.

2.4.4 ENVIRONMENTAL LOADS CALCULATION
After data collection and the selection of the allocation criteria, a model of environ-
mental loads calculation is set up for the product system. One of the most efﬁcient
alternatives using an eco-vector will be presented next.
According to Castells et al. (1995), in the LCI analysis the assignment of the
environmental loads to the different ﬂows of a process and the realization of the
corresponding balance are carried out by a methodology based on an eco-vector.
The eco-vector (v) is a multidimensional mathematical operator in which each
dimension or element corresponds to a speciﬁc EL. In an LCA study, each elementary
ﬂow is associated with an eco-vector with information about natural resource deple-
tion and/or waste releases generated along the product system in study.
In this framework, each mass ﬂow from the system (kg/s) has an associated eco-
vector (v) whose elements are expressed in speciﬁc mass bases. The most common
alternative units are kilograms of pollutant per kilogram of product in cases of mass
units, and kiloJoule per kilogram of product regarding energy units. ELs that cannot
be expressed in terms of mass or energy (e.g., radiation or acoustic intensity) are
transduced in terms of eco-vector as ELs per product mass unit (EL/kg product).
An important aspect of the use of eco-vectors to calculate environmental load
is that each eco-vector must be expressed in units that can be accumulated in order
to carry out material and energetic balances.

 (kg / kg) or (EL / kg) 
 
 Renewable Raw Material 
Not Renewable Raw Material 
 
 Air Emissions 
 Liquid Emissions 
v =   (2.1)
m
 Solid Waste 
 Energy Losses 
 
 Radiation 
 
 Noise 
 Other Environmental Impacts  

Expression 2.1 shows a mass eco-vector (v ) in which different kinds of envi-
m
ronmental loads are grouped. Examples of database lists with environmental loads

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