Environmental news No. 80 2005 – Spatial differentiation in LCA impact assessment

It was realised already during the EDIP programme (1991-96) that the exclusion of spatial information from the characterisation in life cycle assessment sometimes leads to obviously erroneous results. Therefore, the EDIP97 methodology and the accompanying PC tool (beta version 1998) were prepared to take into account spatial differentiation in characterisation, but the concept was not made operational by then. Spatial information was mainly used in the valuation as a basis for identifying obviously false results that could influence the decision to be based on the LCA.

As part of the Danish LCA Methodology and Consensus-creation Project, the uncertainties posed by refraining from spatial differentiation in characterisation were analysed, and methodology was developed to allow inclusion of spatial knowledge about sources and the subsequent receiving environment in the life cycle impact assessment. The purpose of this Guideline is to give an operational presentation of the recommendations following from this project. The new methodology is called EDIP2003. It is presented as an alternative to the EDIP97 methodology as originally presented in Wenzel et al., 1996 and Hauschild, 1996 and later updated in Wenzel et al., 1997 and Hauschild and Wenzel, 1998a. The main innovation of the EDIP2003, compared to the EDIP97 methodology, lies in the consistent attempt to include exposure in the characterisation modelling of the main non-global impact categories. This is accomplished through inclusion of a larger part of the causality chain and through introduction of spatial differentiation regarding the emission and the receiving environment. EDIP2003 can be used both with and without spatial differentiation. In both cases, the inclusion of a larger part of the causality chain gives the EDIP2003 impact potentials a higher environmental relevance and makes them easier to interpret in terms of damage to the protection areas of the LCA.

It is the hope of the project group that the EDIP2003 methodology will find a natural position as an alternative to the EDIP97 method for life cycle impact assessment and in time, when the users get acquainted with the advantages that it offers, replace the EDIP97. Apart from increasing the environmental relevance of the results, it is our judgement that the new method considerably improves our understanding of the spatially determined variation, which underlies the assessment of environmental impacts in LCA, without requiring much additional time and resources.

In this chapter, the EDIP2003 methodology for life cycle impact assessment is introduced and the main differences to the EDIP97 methodology are identified and discussed. First, in Section 1.1, the Guideline's recommendations on the future use of EDIP2003 and EDIP97 are presented in short form. The rest of the chapter gives the background for the EDIP2003 methodology and the recommendations. Section 1.2 introduces the general principles of life cycle impact assessment (LCIA) given in the ISO standard 14042. This is followed by a status on the inclusion of spatial differentiation in current characterisation and normalisation of LCA in Section 1.3. Here, a brief discussion is given of the possibility to include spatial information in LCIA. In Section 1.4 the EDIP2003 and the EDIP97 methodologies are compared and the main differences identified, and in Section 1.5 a three-step procedure for the practical application of the new factors is presented. The application of the EDIP2003 methodology is illustrated throughout the Guideline by an example that is introduced at the end of the introductory chapter in Section 1.6 where an inventory is presented. For each of the impact categories in the following chapters, the use of the EDIP2003 factors is demonstrated on this inventory, and in Chapter 10 at the end of the Guideline all the results are gathered and the example concluded.

The rest of the Guideline is devoted to the description of how the EDIP2003 methodology handles the environmental impact categories currently made operational within the EDIP methodology. Each impact category has its own chapter presenting a procedure for the application of the methodology together with the relevant factors for characterisation and normalisation and guidance for interpretation of the results.

It is the purpose of the Guideline to give an operational presentation of the EDIP2003 methodology for the potential user. The reader looking for a more detailed discussion of the reasoning behind the new methodology is referred to the documentation given in the background report (Potting and Hauschild, 2005).

1.1 Guidance on the use of EDIP97 and EDIP2003

EDIP2003 can be used both in a site-generic and a site-dependent form. The site-generic form does not take spatial variation into account. EDIP97 is site-generic by nature, and the site-generic form of EDIP2003 can replace EDIP97 for all applications.

The main reason to continue the use of EDIP97 would be to ensure compatibility of new results with earlier results obtained using EDIP97. Since some of the impact categories are modelled differently in EDIP97 and EDIP2003, the impact profiles are not directly comparable. On the other hand, the impact profiles of earlier studies can be replaced by EDIP2003 impact profiles by simply applying the new characterisation and normalisation factors to the old inventory. The practical application of the site-generic form of EDIP2003 factors proceeds in the same way as the application of the EDIP97 factors.

The Danish LCA methodology and consensus-creation project gives the following recommendation on the characterisation part of life cycle impact assessment:

The EDIP2003 characterisation methodology as documented in this Guideline can be used as analternative to EDIP97 for performing site-generic characterisation. For the non-global impact categories EDIP2003 provides the option to quantify and reduce the spatial variation resultingfrom differences in the region of emission.

For the global impact categories global warming and stratospheric ozone formation, the EDIP2003 also involves an update of the characterisation factors from EDIP97.

For new studies, the site-generic form of EDIP2003 should be preferred due to the higher environmental relevance of its impact potentials, and because it offers the possibility of quantifying spatial variation.

Site-dependent characterisation
For the non-global impact categories, regional differences in source and receptor characteristics may strongly influence the impact from an emission. The same emitted amount of a substance may thus cause quite different impacts depending on where the emission is released. This spatially determined variation can be quantified using the site-generic form of the EDIP2003 methodology. The site-dependent form of EDIP2003 allows reducing this variation:

Where relevant to the goal of the LCA, the EDIP2003 methodology can be used in its site-dependent form to identify the main sources of spatially determined variation for the non-global impact categories and to reduce the variation to the desired level.

For the impact categories acidification, photochemical ozone formation and terrestrial eutrophication, the site-dependent EDIP2003 factors can be used directly for characterisation. Until the methodology has been implemented in a PC tool, the most operational way of performing spatial characterisation will be

For the impact categories human toxicity, ecotoxicity and aquatic eutrophication the developed spatial characterisation can be applied as part of a sensitivity analysis to examine the spatial variation in exposure that is disregarded when site-generic characterisation is used.

The practical application of spatial characterisation is outlined in Section 1.4 and described for each of the non-global impact categories in the respective chapters throughout the rest of this Guideline. The choice of whether or not to apply spatial differentiation in the LCIA must be made according to the goal of the study. For many applications of LCA, it is in line with the goal of the study that the impact assessment should give the best prediction of the environmental impacts that are caused by the emissions from the product system through reduction of the spatially determined variation.

There are, however, applications of LCA, where the information provided through inclusion of spatial differentiation may not be relevant to the goal of the study. This can be the case for preparation of environmental product declarations and ecolabel criteria. Here, the goal may be to guide consumers to buy products from companies that seriously work on emission reductions over the product's life cycle. Taking into consideration the company's location and the sensitivity of the receiving environment will not contribute to the delivery of that message and may even be misused to obscure it. Therefore, spatial differentiation in life cycle impact assessment does not conform with the goal of such a study. Similar considerations can be made for the application of LCA for development of ecolabel criteria where distinction according to the location of the company may be seen as a hidden tradebarrier. For such applications, EDIP2003 in its site-generic form or alternatively EDIP97 should be used.

When applying the EDIP2003 methodology in its site-dependent form, it must be remembered that it has been developed for use in an LCA context where the perspective is reduction of emissions and their environmental impacts. Here, it offers an improved modelling of the environmental impacts from a product system. The emission reduction perspective is important. The site-dependent EDIP2003 methodology is thus not intended to support impact reduction through transfer of polluting activities to regions where the receiving environment is more robust. Rather it is developed to help prioritising those processes where emission reduction is most urgent and effective.

Normalisation and weighting
Normalisation in EDIP2003 proceeds in the same way as in EDIP97 just applying the EDIP2003 normalisation references which are given for the different impact categories in the respective chapters of this Guideline. Until the default EDIP weighting factors, which are based on political reduction targets, have been updated to an EDIP2003 version, the weighting factors based on EDIP97 factors are used also in EDIP2003.

For the EDIP97 impact categories nutrient enrichment and photochemical ozone formation, the EDIP2003 methodology operates with sub categories. The impact potentials of these sub categories must be aggregated prior to weighting to allow use of the default EDIP97 weighting factors (based on distance to political targets). The sub category impact potentials are normalised against their respective normalisation references and the average of the normalised impacts is taken as the impact potential of the main category.

To accommodate future needs for life cycle impact assessment, both EDIP97 and EDIP2003 are planned to be implemented in the officially endorsed PC tool supporting the use of LCA in Denmark.

1.2 Life cycle impact assessment

According to ISO 14042, the assessment phase of an LCA proceeds through several steps from the inventory to the interpretation:

While classification, characterisation and interpretation are mandatory steps according to ISO 14042, normalisation and weighting are optional.

ISO 14042 also requires that the model for each indicator should be scientifically and technically valid, using a distinct identifiable environmental mechanism and/or reproducible empirical observation. The model should preferably be internationally accepted i.e. based on an international agreement or approved by a competent international body and value choices and assumptions made during the selection of impact categories, indicators, and models should be minimised. Furthermore, the indicators should be environmentally relevant

The EDIP2003 methodology meets all of these ISO 14042 requirements and recommendations.

1.3 Spatial differentiation in characterisation and normalisation

This section reviews the background of spatial differentiation in life cycle impact assessment and defines three levels of spatial differentiation.

The impacts caused by an emission depend on and can be predicted from knowledge about

1)the quantity that is emitted
2)the properties of the emitted substance
3)the properties of the emitting source and the receiving environment

In life cycle assessment, the information under 1 is found in the inventory for the product system. The inventory lists the emissions per functional unit and serves as the starting point for the impact assessment phase.

The properties referred to under 2) could be physico-chemical data like boiling point and molecular weight or biological information regarding the toxicity to specific organisms or the inherent biodegradability of the substance. This kind of information depends only on the substance and can be determined independently. This kind of data is often found in large substance-databases.

The properties under 3) are specified by the conditions under which the emission takes place and the state of the receiving environment to which the emission contributes (e.g. the simultaneous presence of other substances or other stressors in the environment which may interact with the emitted substance to create additive or perhaps synergistic or antagonistic effects). The location of the receiving environment follows from the spatial characteristics of the source, in particular its geographical location.

Some of the early life cycle assessments only included the information under item 1), i.e. all the emissions were simply added and the total emitted quantity was taken as an indicator of the environmental impact. This came in fact down to nothing more than an extended resource and energy analysis and it was quickly realised that this approach was far too simplistic, and that the outcome made little sense in an environmental interpretation. Therefore, a life cycle impact assessment developed which is based on information included under both item 1) and 2) by also taking into account the inherent properties of substances and their maximum capacity to contribute to different environmental impacts with varying strengths. In current practice, the features covered under item 3 are poorly represented, if at all, and variations in the characteristics of source and the receiving environment have hitherto been neglected for a number of reasons:

Due to these reasons, LCA seemed unable to operate with actual concentrations and subsequent risks. In addition, many LCA practitioners have felt that since prediction of actual risks is done using risk assessment tools, there is no need for inclusion of spatial differentiation in LCA. LCA has historically been seen as a tool for pollution prevention, not avoidance of environmental risks at specific sites.

Some of these points used to be regarded as practical limitations but, as we hope to demonstrate with this Guideline and the technical background report behind it, they do not have to be so any more. Moreover, there is no discussion in LCA circles that, as long as an impact category is not global, the spatial variation may be large between process emissions of the same substance. Depending on the goal of the study, it is thus very relevant to include it in the modelling in order to give a correct impression of the impacts caused by the emissions (Udo de Haes et al., 1999). Disregarding spatial variation will increase the possibility of making wrong conclusions and sub optimisations based on the outcome of the life cycle impact assessment. On the other hand, as mentioned earlier, there are applications where the goal of the study and the intended use of the results make the inclusion of spatial differentiation unwanted.

To overcome the methodological limitations quoted above, three levels of spatial differentiation in characterisation modelling have been defined:

LCA is normally not focused on the local impacts from the product system and furthermore, in LCA it will rarely be possible to operate with site-specific modelling for more than a few processes in the product system. Therefore, the site-specific level of spatial differentiation is not envisaged to become an integral part of characterisation modelling. It may still be used to provide additional information for the interpretation step of LCA.

The spatial information available for individual processes in LCA will normally support site-dependent impact modelling. For most processes it will be known at least in which country it is located. This information is required as part of the system delimitation in order to develop transportation scenarios for the product system. The site-dependent level is the level of spatial differentiation that is suggested for characterisation modelling in EDIP2003. Incidentally, at least for most airborne emissions, it is also the level of spatial differentiation that is relevant since it represents their typical scale of dispersion. This means that the site-dependent characterisation factors recommended in Section 1.1 are robust in the sense that the introduction of new uncertainties with the additional fate modelling generally is more than compensated for by the reduction in the impact potentials' spatially determined variation.

In some life cycle assessments, there will be materials or processes, for which spatial information is not available at all. Maybe the data has been aggregated over several suppliers to hide sensitive information or to provide average data. For this situation, the EDIP2003 site-generic characterisation factors can be used to provide impact potentials compatible with the site-dependent impact potentials from other parts of the life cycle. In addition, the use of the EDIP2003 site-generic characterisation factors offers the possibility to quantify the range in the possible impact resulting from ignoring spatial differences in sources and receiving environments.

1.4 EDIP97 and EDIP2003 – similarities, differences and interpretation

After a brief summary of similarities between EDIP97 and EDIP2003, the main differences between the two methodologies are presented and guidance is given on the interpretation of the site-generic and the site-dependent EDIP2003 impact potentials.

Similarities between EDIP2003 and EDIP97
The impact assessment methodologies of EDIP97 and EDIP2003 show many similarities. They are both environmental theme-methods in accordance with the requirements of ISO 14042 and proceed through the same steps – characterisation, normalisation including possible aggregation of sub categories and weighting by the same default weighting factors. They also cover the same impact categories, though some new sub categories are addressed in EDIP2003. For the impact categories aquatic eutrophication, human toxicity and ecotoxicity, the site-generic characterisation factors of EDIP2003 are identical to the EDIP97 factors.

EDIP2003 covers a larger part of the causality chain
Apart from the spatially resolved modelling, the main difference between EDIP97 and EDIP2003 lies in the choice of category indicator. In EDIP97 the characterisation modelling is focused rather early in the environmental mechanisms for some of the impact categories, and the characterisation factors are based exclusively on knowledge of properties of the emitted substance, disregarding properties of the receiving environment. Where the substance's fate is modelled, a uniform environment is assumed ("unit world"). This reflected state-of-the-art when EDIP97 was developed. In contrast, some of the EDIP2003 category indicators are chosen later in the causality chain and the characterisation factors also include the (spatially resolved) modelling of the dispersion and distribution of the substance, the exposure of the target systems and in some cases also the background situation of the target systems to allow assessment of the exceedance of thresholds. This change reflects the development of environmental modelling since the EDIP97 factors were established in 1994 or 1995 (Wenzel et al., 1996, Hauschild, 1996). The difference is illustrated in Figure 1.1

Modelling the impacts further along the causality chain in EDIP2003 increases the environmental relevance of the calculated impacts – they are often in better agreement with the actual environmental effects that are observed from the substances, and they are easier and more certain to interpret in terms of environmental damage. Even though EDIP2003 includes a larger part of the causality chain, the calculated impacts are still predictions and must thus be considered as potentials and not as actual effects. The accuracy of these predictions may be affected by other conditions inherent in the life cycle assessment approach (e.g. focus on the functional unit and aggregation across time).

EDIP2003 supports quantification of spatially determined variation The EDIP2003 site-generic characterisation factors are calculated as the mean of the site-dependent characterisation factors. While still supporting site-generic characterisation, EDIP2003 also allows quantification and reduction of the spatially determined variation in impact through the inclusion of spatial variation in emission sources, and subsequent dispersion and receiving environment exposure. Classes of emission sources are typically defined at the national level.

Figure 1.1 Causality chain. For each link the descriptors identify aspects to consider in an environmental model. The EDIP2003 methodology covers the major part of the chain and includes the spatial variations in the relevant parameters, while the EDIP97 is based on the first links and hence refrains from spatial differentiation.

EDIP2003 provides improved modelling of photochemical ozone formation
Some important additional improvements are obtained with the EDIP2003 methodology. For photochemical ozone formation, the contribution from NOx can now be represented in the site-generic as well as the site-dependent impact potential. The contribution of NO_x has hitherto been omitted from the calculation of the photochemical ozone formation potential but it turns out to be at least the same size as the contribution from the VOCs - hitherto counted as the only source for ozone formation.

EDIP2003 provides improved modelling of acidification
For acidification, the EDIP2003 factors account for the assimilation of nitrogen by ecosystems which in the real world reduces the acidifying properties of nitrogen compounds compared to e.g. SO₂. The EDIP2003 factors thus give a more realistic proportion between the different acidifying compounds than the EDIP97 factors that only reflect the potential for release of protons.

For the EDIP2003 characterisation factors for acidification and photochemical ozone formation, damage to natural ecosystems and human health are chosen as the most sensitive end point. They are also the end point that current regulation is focused on. Therefore damage to man-made materials is not explicitly addressed by the factors for photochemical ozone formation and acidification (although it will typically be represented indirectly by the other indicators). One might thus say that some of the damage covered by EDIP97 is no longer covered in EDIP2003 because the impact indicator is chosen further in the causality chain. As an example for acidification, the impact calculated with the EDIP97 factors represents the number of protons formed per mole of substance emitted. Being defined so early in the cause-effect chain, the EDIP97 impacts in principle represent any damage potentially caused by the protons (i.e. also damage to man-made materials). On the other hand, the relation between proton-release as such and damage caused is often highly uncertain. If, however, there is a wish to explicitly include acidification damage to man-made materials, these may be calculated separately using e.g. the EDIP97 factors. It should be noted, however, that the default weighting factors applied in EDIP97 as well as EDIP2003 represent political reduction targets that for acidification are based on targeted reductions in damage to natural ecosystems. The same holds true for most of the other impact categories – where the political reduction targets expressed in the weighting factors aim at protection of ecosystems or, where relevant, human health.

The difference in choice of category indicators means that for some of the impact categories, the variation estimates provided with the site-generic EDIP2003 factors are not directly applicable to the EDIP97 factors.

Different units for EDIP2003 and EDIP97
The difference in choice of end points also means that the impacts calculated using EDIP97 factors and EDIP2003 factors have different units. For EDIP97 most of the impacts are expressed as quantities of a reference substance which would cause the same size of impact. For EDIP2003, the units express what impact is effectively caused, sometimes up to inclusion of the damage to the target system. In the example of acidification, the EDIP97 unit is "g SO₂-equivalents" while the EDIP2003 is "m² unprotected ecosystem" expressing the area of ecosystem that is moved from an exposure below to an exposure above the critical load and thus potentially damaged.

The EDIP2003 impacts could very well be scaled into emissions of reference substances as was done in EDIP97 but we have chosen to keep the original EDIP2003 units for two reasons:

EDIP2003 optimises the trade-off between environmental relevance and model uncertainty
As characterisation modelling is extended to include more of the causality chain, the uncertainty in interpretation is typically reduced as the environmental relevance of the predicted impact is increased. On the other hand, the introduction of additional environmental models into the calculation of characterisation factors also introduces some additional sources of uncertainty. Spatial differentiation may further reduce the impact uncertainty. At the same time, the information about process locations from the inventory analysis that supports spatial characterisation will sometimes be based on assumptions and may then also be a source of additional uncertainty. Figure 1.2 illustrates this trade-off.

Figure 1.2 As characterisation modelling proceeds along the causality chain to include larger parts of the environmental mechanism, environmental relevance of the calculated impacts is increased and uncertainty of interpretation is reduced (e.g. through reduction of spatially determined variation). At the same time additional uncertainty is introduced through the applied models and the assumptions made e.g. in the geographical scoping of the product system (the figure was developed together with professor O. Jolliet, EPFL).

The recommendations given in this Guideline on spatial differentiation in life cycle impact assessment attempt to optimise the trade-off illustrated in Figure 1.2. This is done within the constraints of the state-ofthe-art in environmental modelling that varies between the different impact categories.

Where detailed integrated assessment models are available, it is possible to develop spatial characterisation factors that incorporate the major part of the spatial variation in emission, exposure and vulnerability of the exposed environment. Here, the resolving power is increased by orders of magnitude compared to the site-generic characterisation, and the additional uncertainty introduced by sophisticated modelling is relatively small in comparison. This is the case for the impact categories acidification, terrestrial eutrophication and photochemical ozone formation. This situation is illustrated by the first of the graphs. For the other non-global impact categories, the state of current environmental modelling is less advanced and as a consequence it has only been possible to include parts of the spatial variation into the new characterisation factors. As a result, the increase in resolving power compared to the existing characterisation is more modest compared to the additional uncertainty which is introduced. This is the case for the impact categories human toxicity, ecotoxicity and aquatic eutrophication.

EDIP2003 improves interpretation through spatially differentiated impact potentials
The main advantage of the site-generic EDIP2003 characterisation methodology lies in the interpretation phase. The site-generic EDIP2003 factors allow the user to quantify a large part of the spatially determined variation, which is inherent but unknown in the EDIP97 characterisation factors, and this is valuable input to the sensitivity analysis. Use of the EDIP2003 site-generic factors does not require any information apart from what is required to use EDIP97. Further sensitivity analysis with the site-dependent factors requires specification of the geographic location of the processes in the product system. For some processes, this specification will be encumbered by an uncertainty that must also be considered in the sensitivity analysis.

As discussed earlier in this section, the impact potentials calculated with the EDIP2003 factors – site-generic as well as site-dependent - are expected to be in better accordance with the actual impacts on several accounts:

This increased environmental relevance of the EDIP2003 impact potentials should be taken into account in the interpretation, particularly in the case, where they are compared to impact potentials of a lower environmental relevance (calculated using characterisation factors of the old type, EDIP97 or others). It should also influence the development of weighting factors based on the environmental relevance of the impact categories (e.g. derived through a panel procedure).

The default EDIP weighting factors, which are based on political reduction targets, should also be updated to an EDIP2003 version using the new characterisation factors on the politically targeted emission levels. This is not a part of the Danish Method Development and Consensus Creation Project and until it has been done, the updated weighting factors based on the EDIP97 factors are suggested used as proxies (Stranddorf et al., 2005).

1.5 How is spatial characterisation performed?

Traditionally, the inventory information is aggregated in the sense that all emissions of one substance occurring through the life cycle of the product are summed. In this way the emission of e.g. SO₂ is reported as one total emission of for the whole life cycle and all spatial information about the individual emissions is lost. If site-dependent characterisation is performed directly (i.e. not as part of the sensitivity analysis following the site-generic characterisation), the life cycle inventory must be passed on to the impact assessment phase in a non-aggregated form in order to make it possible to identify the geographical location where the different processes take place. This will not be a problem when the EDIP2003 methodology is integrated in an LCA software but may otherwise create some additional work compared to the site-generic EDIP2003 or EDIP97.

Until the site-dependent form of EDIP2003 is implemented in a PC tool, a practical application of spatial characterisation is described for each of the non-global impact categories in the respective chapters throughout the rest of this Guideline but in general terms the recommended way of applying EDIP2003 manually is:

Repeat step 2 until the spatially determined variation is reduced to a suitable level, i.e. a level where the spatially determined variation can no longer change the conclusion of the study.

The only extra information that is required to use the site-dependent factors of EDIP2003 is the country in which the process is located. This information is often known as part of the scoping. For processes, where this information is not at hand, the site-generic EDIP2003 factors can be applied. This is also the option for processes taking place outside Europe.

Aggregation of sub categories
For two of the EDIP97 impact categories (nutrient enrichment and photochemical ozone formation), EDIP2003 operates with sub categories which must be aggregated prior to weighting to allow weighting with the default EDIP97 weighting factors (based on distance to political targets). The aggregation procedure for sub categories that was developed under EDIP97 to prepare the sub categories of ecotoxicity and human toxicity for weighting is also used here; First the sub category impact potentials are normalised against their respective normalisation references. Then their average is calculated to represent the impact potential of the main category.

In principle, the default EDIP weighting factors, which are based on political reduction targets, should also be updated using the new characterisation factors for application to impact potentials calculated using these new factors. This has not been done yet and has not been a part of the Danish Method Development and Consensus Creation Project. It would be relevant with an update for the impact categories acidification, terrestrial eutrophication and photochemical ozone formation. For the other impact categories, the site-generic version of EDIP2003 is identical to EDIP97 and the weighting factors are therefore the same. The difference is not expected to be dramatic and until an update is available, it is suggested to use the updated EDIP97 weighting factors as proxies for all impact categories.

1.6 Example on the use of EDIP2003

The following example serves to demonstrate the procedure for application of the EDIP2003 site-generic and site-dependent characterisation factors for all the impact categories. The example has been constructed to illustrate the use of spatial characterisation. The example is introduced here, and the characterisation is performed and illustrated throughout the chapters on the individual impact categories. A comparison and discussion of the results is given in Chapter 10.

In the construction of an office chair, the product developer has to make a choice between the use of zinc and the use of a plastic (polyethylene) as material for a supporting block (a structural element) in the seat of the chair. The supporting block is flow injection moulded (20 g plastic) or die cast (50 g zinc). A life cycle assessment is performed to compare the environmental impacts from each of the two alternatives. The functional unit (f.u.) of the study is one component made from either plastic or zinc.

An excerpt from the inventory analysis provides the following results for the life cycle impact assessment:

Table 1.1. Excerpts from inventory for one supporting block made from plastic or zinc