Impact Assessment
 The inventory table is the most objective result of a LCA study. However, a
long list of substances is difficult to interpret.
Life Cycle Impact Assessment (LCIA) is used for systematic evaluation of the impacts.
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Tutorial to start your first LCA example in the SimaPro demo. Introduction Two problems exist in impact assessment: - There are not sufficient data to calculate the damage to ecosystems by an impact.
- There is no generally accepted way of assessing the value of the damage to ecosystems if this damage can be calculated.
One of the oldest impact assessment methods is the EPS (Environmental Priority Strategy) system as developed by the IVL in Sweden. In this method, the complete chain of cause and effect from each impact on a human equivalent is calculated. Another method is the Ecopoints method, developed for the Swiss government. It is based on the distance-to-target principle. The distance between the current level of an impact and the target level is assumed to be representative of the seriousness of the emission. PRé Consultants developed the Eco-indicator 99 and Eco-indicator 95
impact assessment methods. back to top Three steps in impact assessment CML and SETAC describe a general approach, through the calculation of environmental effects. There are three steps: 1. Classification and characterization
2. Normalization
3. Evaluation or weighting The procedure is described below using fictional data. Step 1: Classification and characterization ClassificationIn the classification step, all substances are sorted into classes according to the effect they have on the environment. For example, substances that contribute to the greenhouse effect or that contribute to ozone layer depletion are divided into two classes. Certain substances are included in more than one class. For example, NOx is found to be toxic, acidifying and causing eutrophication.
Characterization
The substances are aggregated within each class to produce an effect score. It is not sufficient just to add up the quantities of substances involved without applying weightings. Some substances may have a more intense effect than others. This problem is dealt with by applying weighting factors to the different substances. This step is referred to as the characterization step.
| Emission |
Quantity (kg) |
Greenhouse |
Ozone layer depletion |
Human toxicity |
Acidification |
| CO2 |
1.792 | x 1 |
- | - |
- |
| CO |
0.000670 | - |
- | x 0.012 |
- |
| NOx |
0.001091 | - |
- | x 0.78 |
x 0.7 |
| SO2 |
0.000987 | - |
- | x 1.2 |
x 1 |
| Effect scores: | |
1.792 | 0 |
0.00204 | 0.0017 |
Example of the characterization step for a small inventory table. Emissions are multiplied by the corresponding weighting factor before they being summed per class. The results are called effect scores.
In the comparison between paper and polyethylene (LDPE) the calculated effect scores can be displayed as a graph. The highest calculated effect score is scaled to 100%. This means the materials can only be compared per effect.
Example of a classification. The highest score is scaled to 100%. The classes are: Greenhouse effect, Ozone layer depletion, Heavy metals, Carcinogen, Winter smog, Summer smog, Pesticides, Energy use and Solid waste disposal (fictional example).
The interpretation of these scores may be less confusing than interpretation of a substance list, but is by no means without problems. If all the scores for one product are higher than those for another, it is easy enough to conclude which is the more environmentally friendly. But if one has a higher score for acidification, while the other has a higher score for the greenhouse effect it becomes difficult to justify such a conclusion. Interpretation depends on two factors: - The relative size of the effect compared to the size of the other effects. In this example it is important to see whether the ecotoxicity score of 100% refers to a very high or an extremely low effect level. This is
called normalization.
- The relative importance attached to the various environmental effects. This is called evaluation.
back to top 2. Normalization In order to gain a better understanding of the relative size of an effect, a normalization step is required. Each effect calculated for the life cycle of a product is benchmarked against the the known total effect for this class. For example, the Eco-indicator method normalizes with effects caused by the average European during a year. Of course it is possible to choose another basis for normalization. Normalization enables you to see the relative contribution from the material production to each already existing effect. The graph below shows such a normalization step (fictional data).
A normalized effect score. The length of the columns is now scaled to a normalized effect score. After normalization it becomes clear that the contributions to ecotoxicity, greenhouse effect, summer
smog and human toxicity are relatively high. The contributions to the other effects are almost negligible (fictional example).
back to top 3. Evaluation or weighting Normalization considerably improves our insight into the results. However, no final judgment can be made as not all effects are considered to be of equal importance. In the evaluation phase the normalized effect scores are multiplied by a weighting factor representing the relative importance of the effect.
After weighting the relative importance of the normalized effect scores is added. After weighting, ecotoxicity has clearly gained in significance (fictional example).
The length of the columns actually represents the seriousness of the effects. This makes it possible to add the columns to calculate a final result.
The weighted scores can be added for a final judgment.
The higher the score, the higher the environmental impact. The graph above clearly shows a preference for paper (fictional example). back to top |
