A multi-criteria decision-making model for classifying wood products with respect to their impact on environment

Although life cycle assessment is frequently used in scientific studies of product comparison, many practitioners are looking for improvements in the normalisation, grouping and weighting of life cycle inventory results. Local conditions, which are well known to local experts, are very important to these steps. The goal of this work was to develop a computer-based decision support system for classifying wood products according to their influence on the environment in their whole life cycle. The model specifically addresses local conditions in the Republic of Slovenia and was developed by Slovenian experts. We used the approach of multi-criteria decision making (MCDM). We developed a multi-attribute model that includes key parameters that influence the burdening of environment. The parameters are organised into a hierarchical structure with several levels in such a way that they form a hierarchy with unidirectional hierarchical relationships between levels. The aggregation of parameter values is carried out by utility functions which were defined according to the analytic hierarchy process method on the basis of 52 experts' findings, which were gathered with the Delphi method in three rounds. The main result is a multi-criteria model for the assessment of wooden products. The model consists of 104 criteria, grouped into 28 subtrees, addressing various processes of production. Each criterion in the model has an associated weight, and each entry criterion has an entry function. The model has been used to assess different product concepts with the purpose of supporting decision making for the environmentally most suitable product concept and for analysing products with the intention of finding out more environmentally friendly products. The weights in the model indicate that a preliminary production of auxiliary materials and energy consumption represents the biggest impact of wooden products on the environment. In preliminary production, the most problematic are preservatives, coating systems and glues. In energy production, the most influential are gasoline and petroleum. Emissions are most affected through water and air, whereas solid wastes and energy emissions are less important. With wastewaters, the most critical is the presence of organic criteria. With waste air, more important is waste air appearing directly in the production and less the smoke gases from devices for acquiring heat and electricity. The presented multi-attribute model is aimed at classifying and comparing products according to their environmental burden in the entire wood product life cycle. The comparison can be carried out not only at the level of entire products but is also decomposed into hierarchically structured criteria. The decomposition reveals distinctive advantages and disadvantages of a product compared to others. The MCDM approach enables a relatively easy adaptation of the model where the changes have only a local effect. Entry data can be provided either directly in a numerical form or indirectly through pairwise comparison of alternatives. The model is restricted in the sense that it specifically addresses local conditions and legislation of the Republic of Slovenia. The parts of the model that address emissions depend on Slovenian legislation and would require an adaptation to other countries. Other parts are fairly general. In order to compare wood products with other alternative or substitutive products, the set of criteria had to be expanded. We also suggest expanding the model with the aspects of working conditions and socioeconomic consequences of production.