LUAS, SA, 1.4.2010
In life cycle assessment, environmental aspects and potential environmental impacts are examined across the entire life of a product, from raw material acquisition to manufacture, use and disposal. The purpose of life cycle assessment is to investigate in detail the full range of environmental impacts, "from cradle to grave", that a studied product or service has. This encompasses raw material and energy consumption, emissions to air, water, and ground, as well as the production of solid waste throughout the life cycle, and the potential environmental impacts caused by them.
In order to make a thorough life cycle assessment, you need a lot of input data and this means that the work takes a lot of time and money. Therefore a thorough life cycle assessment is worthwhile only with products that have considerable environmental impacts or a large sales volume. In practice the most common choice is to conduct a smaller-scale, simplified life cycle assessment, which has been "tailor-made" for a particular purpose.
In the 1990s there emerged a need to standardize life cycle assessment, when two assessments on similar types of packages differed from each other distinctly. The international ISO standard of life cycle assessment was published in 1997. Life cycle assessment is dealt with in standard series ISO 14040-3, which is being updated at the moment.
Life cycle assessment consist of following main phases:
1. Definition of the goals and scope
2. Inventory analysis
3. Impact assessment
4. Interpretation of results
5. Critical review
Source: ISO 14040 -3
The goals and scope of life cycle assessment must be defined carefully, because at this stage you make decisions about delimitation and approach that are significant for the whole process. This is the planning stage of life cycle assessment.
In the definition of the goals you must clearly indicate the intended application and the reasons for making the life cycle assessment. In addition, you must determine who will be informed of the results of the life cycle assessment. The functions of the product must be clearly defined, i.e. the performance of the product must be described. A functional unit provides a quantitative expression of these functions. The unit must be clearly defined, and measurable. The primary purpose of the functional unit is to serve as a reference unit for the input data and results. With the help of the reference unit it is possible to ensure that the results of life cycle assessment are comparable. After defining the functional unit, you must establish the number of products needed for the function to take place, the so-called reference flow.
The scope of application for the life cycle assessment must be defined in sufficient detail. The comprehensiveness, depth and specificity of the assessment must correspond to the objectives and be sufficient in relation to the objectives defined. During the assessment, the scope of application may have to be modified, as more data is acquired.
When planning life cycle assessment, you must determine the boundaries of the assessment, i.e. which unit processes will be studied. You must also decide which environmental emissions will be assessed and how detailed the assessment will be. All decisions to omit phases, processes, or inputs/outputs of the life cycle must be clearly documented and justified.
These life cycle stages, unit processes and flows must be considered during the planning phase:
- inputs and outputs of the manufacturing/processing phase
- production and use of fuels, electricity and heat
- handling of process waste and discarded products
- manufacture of ancillary materials
- manufacture, maintenance and decommissioning of production equipment and machinery
- additional operations, such as lighting and heating
- use and maintenance of the products
- utilization of used products (e.g. reuse, recycling, recovery of energy)
- other considerations related to impact assessment
Using process flow charts makes it easier to illustrate the system. The charts describe the unit processes and how they are related to each other. In connection with each unit process, you should determine the starting point (acquired raw materials or semi-products), operations conducted during unit process and destination of the semi-products or end products.
During the planning phase you decide which material inputs are included in each unit process assessment. These criteria are often used when choosing the inputs
- mass, i.e. choosing the inputs that are needed in big quantities in the process
- energy, i.e. choosing the inputs the processing of which requires the most energy
- environmental considerations, i.e. choosing the inputs that have the most significant impacts on the environment
In the planning phase you also decide how to classify the input data, e.g. whether the emissions from a unit process are divided into emissions to air, water and ground.
Sources: ISO 14040, ISO 14041
Inventory analysis consists of collecting data and completing calculations. Here you define the environmental burden of the product system, i.e. all the inputs and outputs (products, emissions, other environmental considerations). There are various methods of data collection. The possible methods include questionnaires, phone enquiries, visits, interviews and existing literature (sources must be mentioned). When collecting the data, you must verify that it is accurate.
What must be considered when collecting data?
- units must be clearly presented, e.g. whether the data is expressed in kilograms of waste water or cubic meters of waste water
- whether the data was collected in normal operational circumstances, in connection with starting/ending operation, or perhaps during a period of sporadic emissions
- where the production plant is located
- what kind of production technology was used at the time of data collection
- how the data was collected and how comprehensive it is
- who collected the data and when
In general, you need to know each unit process well in order to be able to collect data. Often some data must also be collected from sources outside the company in question e.g. from subcontractors or clients.
In its simplest form, an inventory analysis can be conducted with a spreadsheet program. There is also special computer software to make it easier and faster to conduct life cycle assessment.
When the desired data has been collected, the material and energy balance of each unit process is calculated, as well as the material and energy balance of the whole product system. However, most industrial processes produce more than one product. Therefore the material and energy flows, as well as the factors changing and burdening the environment, must be allocated to different products.
Source: ISO 14041.
In life cycle assessment, the purpose of impact assessment is to provide a better view of the environmental impacts, with the help of the results of the inventory analysis. The impact assessment phase involves describing the chosen environmental issues, called impact categories, and using impact category indicators to summarize and explain the results of the inventory analysis. The components required for impact assessment are:
- selecting impact categories, impact category indicators and characterization models
- classification, i.e. sorting LCI results into impact categories
- characterization, i.e. calculating the indicator result of the impact category
The most widely used impact categories are e.g. energy consumption, consumption of natural resources, climate change, ozone depletion, acidification, eco-toxicological effects, toxicological effects, and eutrophication. It is easiest to model impact categories that concern global problems, such as greenhouse effect and ozone depletion, for which there is an international scientific forum (confirming the characterization models and coefficients to be used in each case).
Impact category indicators differ from their scientific foundation, because environmental process models contain varying amounts of uncertainty, as well as choices made on the basis of values and/or common consent.
The characterization model should be valid both scientifically and technically, and it should be based on some identifiable environmental mechanism and/or experimental observation. In practice, the characterization models used today contain simplifications, and therefore they provide potential environmental impacts, instead of actual impacts.
The impact categories, impact category indicators and characterization models should be internationally accepted.
In classification the results of the inventory analysis are sorted into environmental impact categories. The modeling of e.g. emission data into impact categories can be done using different kinds of characterization coefficients. A characterization factors is a factor derived from the characterization model, which is used to convert the results of the inventory analysis to the common unit of the impact category indicator. Characterization should be based on scientific knowledge that is as reliable as possible.
Voluntary components of impact assessment are:
- normalization (calculation of the indicator results of the impact category in relation to reference data)
- qualitative analysis of the input data
Normalization helps to see in which impact category the options being studied have the relatively biggest impact. In grouping, impact categories can be put into one or several groups. Impact categories can be grouped e.g. in the order of importance.
In weighting, the indicator results of different impact categories are evaluated relative to each other: are some impacts more serious than some others? The indicator results of the impact categories are modified with the help of numerical factors chosen through value judgement. In the process of impact assessment, weighting the impact categories is a non-scientific part, emphasizing subjective choices, and that is why here lie the greatest difficulties of impact assessment. Determination of the values must be transparent.
Source: ISO 14042
The last stage of life cycle assessment is interpretation of the results. It is a systematic process where the most important results of the inventory and impact assessment are identified, evaluated and checked. The results are reported in a transparent manner, in accordance with the goals of the field of application. Interpretation of the results aims at recommendations and conclusions, which support decision making. When interpreting the results, you consider the uncertainties that can emerge at different stages of assessment. Possible uncertainties can be connected with e.g.
- assumptions and scoping done at the beginning of the work
- collection of data
- using input data based on average values
- outdated or otherwise incomplete data
- determination of the functional unit of the product
- excluding some of the life cycle phases of the product from the assessment
- computer models used to help assessment
- allocation, i.e. allocating material flows and loads to different products and product systems
The result interpretation stage consists of three parts:
- identification of the significant issues (e.g. inventory data categories, impact categories or life cycle stages that have a substantial effect on the results)
- evaluation (completeness check, sensitivity check and consistency check)
- conclusions, recommendations and reporting
The goal of the completeness check is to ensure that all relevant information and input data needed for the interpretation are available and sufficient. The goal of the sensitivity check is to evaluate the reliability of the results and conclusions by determining the effect of the uncertainty connected e.g. with input data, allocation methods or calculation of the indicator results of impact categories. The goal of the consistency check is to determine whether the hypotheses, methods and input data are consistent with the objective and scope of the assessment.
Source: ISO 14043
So far life cycle assessments have not been critically analyzed, chiefly because it would increase the costs of life cycle assessments. However, the ISO standards express the requirement for critical evaluation, and therefore this kind of evaluation is likely to become more common. Life cycle assessment can be critically reviewed at a single stage, after the assessment has been completed. Reviewing can also be done in several stages. A multi-stage review is better than a single-stage review at the end of the process, because in this way the critique can be more easily used to improve the assessment.
Critical reviewing can be done by an internal expert, an external expert or as an inspection performed by stakeholder groups. Usually external reviewers are considered more reliable, since they do not have a connection to the company or organization conducting the life cycle assessment. A thorough critical review takes about 10 % of the cost and time used for the study. One of the most important functions of the critical review is to ensure that the methods used in the life cycle assessment meet the standard.
In general, critical reviewing must ensure that
- the methods used in the life cycle assessment conform to the ISO 14040 standard
- the methods used in the life cycle assessment are scientifically and technically valid
- the data used is suitable and sensible in relation to the objectives of the assessment
- the conclusions are in accordance with the identified limitations and the objectives of the assessment
- the life cycle assessment is transparent and consistent
A suitable critical reviewer is a person that has the required scientific and technical expertise, has sufficient professional experience of conducting life cycle assessments and preferably knows the product and functional unit being assessed. It is an absolute requirement that the reviewer is reliable. The reviewer must also be independent, in other words he must not have business connections to the performer of the assessment.
SOURCEISO 14040 In life cycle assessment all the starting hypotheses and data must be clearly stated.