Analyzing uncertainty in a comparative life cycle assessment of hand drying systems
The goal of this study is to evaluate and compare the environmental impact (with a focus on global warming potential) of five hand drying systems: hands-under (HU) dryers, high-speed hands-under (HSHU) dryers, high-speed hands-in (HSHI) dryers, cotton roll towels, and paper towels. Another objective is to incorporate uncertainty into this comparative life cycle assessment (LCA) as a means of understanding the statistical robustness of the difference between the environmental impacts of the hand drying systems.
We conducted a life cycle assessment in accordance with the ISO 14040/14044 standards using data primarily from publicly available reports. As part of the study, we performed a parameter uncertainty analysis for multiple scenarios to evaluate the impact of uncertainty in input data on the relative performance of products. In addition, we conducted a probabilistic scenario analysis of key drying system parameters in order to understand the implications of changing assumptions on the outcomes of the analyses.
Results and discussion
The scope of the analyses enabled us to draw robust conclusions about the relative environmental performance of the products. We can say with a high degree of confidence that the high-speed dryers have a lower impact than paper towels and cotton roll towels. Differentiating the performance of the hand dryers requires being more specific about framing assumptions. Under certain conditions, the HSHI dryer is expected to have a lower impact than the HU and HSHU dryers. However, under other conditions, one cannot say that the HSHI dryer is clearly better than the other dryers. We cannot differentiate the performance between the HU dryer, cotton roll towels, and paper towels.
This work demonstrates the importance of going beyond traditional uncertainty analyses for comparative LCAs that are used for assertions of relative product environmental impact. Indeed, we found instances where the conclusions changed as a result of using the probabilistic scenario analysis. We outline important elements that should be included in future guidance on uncertainty analyses in comparative LCAs, including conducting parameter and scenario uncertainty analyses together and then using the outcomes to guide selection of parameters and/or choices to analyze further.
KeywordsLife cycle assessment Hand drying systems Parameter uncertainty Scenario analysis
- Adams C (2007) What’s better for the environment, electric hand dryers or paper towels? http://www.straightdope.com/columns/read/2721/whats-better-for-the-environment-electric-hand-dryers-or-paper-towels
- British Standards Institute (2008) Publicly Available Specification 2050:2008: specification for the assessment of the life cycle greenhouse gas emissions of goods and services. London, UKGoogle Scholar
- Clarren R (2007) Public bathroom dilemma: paper or air? Salon. http://www.salon.com/2007/11/12/bathroom_dilemma/
- Dettling J (2009) Comparative environmental life cycle assessment of hand drying systems: the XLERATOR hand dryer, conventional hand dryers and paper towel systems. Quantis US, Boston, US. http://www.exceldryer.com/PDFs/LCAFinal9-091.pdf
- Dyson (2010) The Dyson Airblade™ hand dryer receives industry first Carbon Reduction Label. http://www.dysonairblade.com/news/newsArticle.asp?newsID=116
- Dyson Airblade Technical Specifications (2011) http://www.dysonairblade.co.uk/specification/default.asp?product=AB01-AIRBLADE
- Eberle U, Möller M (2006) Life cycle analysis of hand-drying systems. A comparison of cotton towels and paper towels. Öko-Institut e.V., Freiburg, Germany. http://www.etsa-europe.org/news/documents/ETSALCAbrochureoncottonrolltowelsJuly06EN.pdf
- Environmental Resources Management (2001) Streamlined life cycle assessment study. Oxford, UK. http://www.airdri.com/script/AirdriBobrick.pdf
- European Commission-Joint Research Centre-Institute for Environment and Sustainability (2010) International Reference Life Cycle Data System (ILCD) Handbook—general guide for life cycle assessment—detailed guidance. Luxembourg. http://lct.jrc.ec.europa.eu/pdf-directory/ILCD-Handbook-General-guide-for-LCA-DETAIL-online-12March2010.pdf
- Franklin Associates (2011) Documentation for the paper calculator. http://www.papercalculator.org/
- Frischknecht R, Jungbluth N, Althaus H-J, Doka G, Dones R, Heck T, Hellweg S, Hischier R, Nemecek T, Rebitzer G, Spielmann M, Wernet G (2007) Overview and methodology. ecoinvent report no. 1. Swiss Centre for Life Cycle Inventories, Dübendorf, Switzerland. http://www.ecoinvent.org/fileadmin/documents/en/01_OverviewAndMethodology.pdf
- Hischier R, Weidema B, Althaus H-J, Bauer C, Doka G, Dones R, Frischknecht R, Hellweg S, Humbert S, Jungbluth N, Köllner T, Loerincik Y, Margni M, Nemecek T (2010) Implementation of life cycle impact assessment methods. ecoinvent report no. 3, v2.2. Swiss Centre for Life Cycle Inventories, Dübendorf, Switzerland. http://www.ecoinvent.org/fileadmin/documents/en/03_LCIA-Implementation-v2.2.pdf
- Intergovernmental Panel on Climate Change (2007) Climate Change 2007: the physical science basis. Contribution of Working Group I to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change, Cambridge, UK. http://www.ipcc.ch/publications_and_data/publications_ipcc_fourth_assessment_report_wg1_report_the_physical_science_basis.htm
- International Organisation for Standardisation (2006) ISO/FDIS 14044 Environmental management-life cycle assessment-requirements and guidelinesGoogle Scholar
- Koerner B (2008) Electric hand dryers vs. paper towels. Slate. http://www.slate.com/id/2193740/
- Madsen J (2007) Life cycle assessment of tissue products. environmental resources management. http://www2.kimberly-clark.com/pdfs/LifeCycleAssessment.pdf
- Montalbo T, Gregory J, Kirchain R (2011) Life cycle assessment of hand drying systems. Massachusetts Institute of Technology, Cambridge, USA. http://msl.mit.edu/publications/HandDryingLCA-Report.pdf
- NSF (2007) NSF Protocol P335: hygienic commercial hand dryers. Ann Arbor, MIGoogle Scholar
- Schryver AD, Vieira M (2008) LCA of two different hand drying systems: a comparative life cycle assessment of non-reusable paper and reusable cotton towels PRé Consultants bv, Amersfoort, The Netherlands. http://www.vendorinternational.com/upload/Engelse%20plaatjes/VendorReport_shortversion.pdf
- Skoczen S (2009) Sustainability showdown: paper towels vs electric dryer. http://www.sixlinks.org/People/Steven-Skoczen/Blog/82/Sustainability-Showdown-Paper-Towels-Vs-Electric-D
- United States Environmental Protection Agency (2009) Municipal Solid waste generation, recycling, and disposal in the United States: facts and figures for 2008. http://www.epa.gov/osw/nonhaz/municipal/msw99.htm
- Watson J (2007) Greener dryer better: LCA of hand dryers vs. paper towels. http://www.treehugger.com/clean-technology/greener-dryer-better-lca-of-hand-dryers-vs-paper-towels.html
- Wettstein D (2009) Ecobalance of emissions with climatic effect resulting from hand drying. myclimate, Zurich, Switzerland. http://www.climatop.ch/tl_files/factssheet/2011/E_Factsheet_Dyson_Handdryer_2011_2013_v2.pdf
- World Resources Institute and World Business Council for Sustainable Development (2011) Greehouse gas protocol: product life cycle accounting and reporting standard. http://www.ghgprotocol.org/files/ghgp/public/Product-Life-Cycle-Accounting-Reporting-Standard_041613.pdf. Accessed 2011