April 17, 2017
By Hans Schleibinger, PhD, Liang Grace Zhou, PhD, Jeff Whyte, and Deepti Bijlani
Radon, a naturally occurring radioactive gas, enters buildings through foundation cracks and other openings in contact with soil and rocks. It is widely acknowledged as the second leading cause of lung cancer after smoking, with Health Canada estimating approximately 16 per cent of the country’s lung cancer deaths to be attributable to radon exposure. (For more information, see “Canadian population risk of radon induced lung cancer: a re-assessment based on the recent cross-Canada radon survey” by J. Chen, D. Moir, and J. Whyte, available at www.ncbi.nlm.nih.gov/pubmed/22874897.) The organization’s cross-Canada residential radon survey estimated roughly seven per cent of Canadians live in homes with radon levels above 200 Bq/m3—the Canadian minimum radon guideline. (This information comes from Health Canada’s “Cross-Canada Survey of Radon Concentrations in Homes Final Report.” Visit www.hc-sc.gc.ca/ewh-semt/alt_formats/pdf/radiation/radon/survey-sondage-eng.pdf.)
The Ventilation and Indoor Air Quality Group of the National Research Council of Canada (NRC) investigates a variety of factors influencing indoor air quality (IAQ), including radon. One of this article’s co-authors, Liang Grace Zhou, has led a team conducting research activities related to radon control in buildings since 2011, in collaboration with Health Canada’s National Radon Program.
The most common techniques to prevent radon entry include active soil depressurization, increasing overall ventilation rates, and avoiding depressurization inside the building. These measures are frequently taken in combination with sealing soil gas entry routes in floors and walls.
In Canadian homes, radon fans are usually installed in basements, meaning assessment of radon leakage through fan enclosures into indoor air is critical. In September 2014, NRC’s radon research team, led by Zhou, successfully designed and constructed the world’s first radon fan leakage test rig to provide answers to four major manufacturers of radon fans in North America. Leakage through eight commonly used radon fans was determined using this rig. This project was the first in the world to scientifically examine radon fan leakage. Therefore, it serves as the only technical basis for radon fan leakage criteria to support Canadian radon mitigation standards currently being developed.
Since December 2014, provisions in the B.C. Building Code for Zone 1 radon-prone areas have required the installation of a full-size vertical passive radon stack extending upward through the building and terminating above the roofline. In 2014 and 2015, the National Building Code of Canada (NBC) standing committee on housing and small buildings received two building code change requests to include such stacks in NBC. To help the standing committee address this change request, NRC’s radon group is currently undertaking a field study of extended passive radon stacks in homes across the country. The outcomes from the field study, combined with two years of lab work in the Canadian Centre for Housing Technology (CCHT) and the Indoor Air Research Laboratory (IARL), will help determine the efficacy of these stacks for radon control. The study will further facilitate development of a passive radon stack practice guide for builders and contractors, and ultimately assist the NBC standing committee in addressing building code change requests.
Testing active soil depressurization systems
Active soil depressurization systems have been used in 80 per cent of professional mitigation cases in North American homes. (For more, see R. Wood’s “Cold Climate Radon Mitigations: A Canadian’s Perspective” at ftp.cmhc-schl.gc.ca/chic-ccdh/Research_Reports-Rapports_de_recherche/eng_unilingual/Ca1%20MH%2010C51_W.pdf.) Although the effectiveness of these systems with indoor radon control has been widely recognized, their impacts and insulation requirements in Canada’s cold climate were previously not fully understood. Between 2012 and 2016, experiments were conducted during winter months in the twin houses of the CCHT—a facility jointly operated by NRC, Natural Resources Canada (NRCan), and the Canada Mortgage and Housing Corporation (CMHC).
These experiments demonstrated the continuous operation of an active soil depressurization system would increase the heating-energy consumption of the house by five per cent annually, and cool down the concrete slab by 2 C (3.6 F). Interestingly, the test results also indicated active soil depressurization systems had insignificant influence on basement air pressure and temperature, soil temperature profiles, and the frost line around the houses. The tests further showed an insulation value of R-14 around the active soil depressurization stack was sufficient under the winter test conditions to avoid ice blockage.
Additionally, tracer gas experiments conducted in the IARL suggested gable-end exhaust at eaves level is a viable solution for routing active soil depressurization termination points to prevent freeze-up/icicle formation. It was also discovered the operation of active soil depressurization would only pose a limited risk of back-drafting from combustion appliances (e.g. wood-burning stoves and natural gas fireplaces).
The CCHT facility has recently been expanded and modernized to represent the trend toward smaller, multi-unit housing and increasingly airtight, energy-efficient design. Four radon prevention and control systems have further been installed in this new facility. Investigations on the performance and impact of these systems will be carried out in the next two to three years.
To position Canada at the forefront of radon control research and assist the building industry in developing radon-ingress solutions tailored to the Canadian climate, the NRC radon research team, in collaboration with Health Canada, developed the world’s first Radon Infiltration Building Envelope Test System (RIBETS),which has been in use since 2013.
RIBETS is a controlled testing system, characterized by a mockup house with a 2 x 2-m (6 x 6-ft) footprint where radon can be introduced in a controlled fashion into the sub-slab area (Figure 1). Floor assemblies containing innovative products such as membranes, concrete, foam board, sprayed polyurethane foam (SPF), concrete forms, drainage systems, or sub-slab ventilation panels can be installed according to manufacturers’ installation guides, then evaluated for their efficiency related to radon prevention and mitigation. The ductwork design of the system makes the facility an ideal test bed to investigate the effectiveness of demand-controlled HVAC components such as heat or energy recovery ventilators, which can also be used for reducing indoor radon level.
Within the first two years of completion, RIBETS had already served five Canadian firms by evaluating various types of innovative products. Performed in conjunction with NRC’s Canadian Construction Materials Centre (CCMC), these tests enabled manufacturers to enter new markets by demonstrating their products’ code compliance as alternate solutions. One client was even able to use the RIBETS results to gain compliance with International Code Council (ICC) standard ICC-AC461, An Alternate Gas-permeable Layer of a Sub-slab Depressurization System for Radon Gas Control, opening up the U.S. market to the product.
NRC has also developed Canada’s first ISO-compliant radon diffusion test chamber—it was developed and commissioned according to the specifications and requirements of ISO/DTS 11665-13, Measurement of Radioactivity in the Environment–Air: Radon 222–Part 13: Determination of the Diffusion Co-efficient in Waterproof Materials: Membrane Two-side Activity Concentration Measurement Method. It supports manufacturers so their products can be evaluated for radon-permeability in a precisely controlled environment with radon activity levels higher than 1.0 MBq/m3, as defined by the ISO standard.
Randi Fox, an architect with Terra Vent Systems Inc., said in an unpublished 2015 interview: “RIBETS is vital to progress in radon mitigation, which is a worldwide concern. With NRC’s radon research and now RIBETS, Canada is gaining ground as a leader in radon solutions.” Federal, provincial, and municipal building officials, the Canadian Home Builders’ Association (CHBA), engineers, architects, environmental and building engineering companies, and home builders are all showing a strong interest in the products that have been evaluated in the radon diffusion test chambers.
RIBETS and the radon diffusion test chamber additions complement NRC’s CCHT and IARL research facilities, as well as further expanding testing capabilities. The NRC radon team can now test and evaluate all relevant approaches dealing with preventing and reducing radon entry, and thus can accommodate the value chain and promote the uptake of verified technologies.
Radon mitigation is a serious business, and it requires facilities and expertise to support the discovery of innovative solutions that can eventually become commonplace. The knowledge gained from these studies enables health regulators to incorporate an increasing number of verified solutions into Canadian radon guidance and standards. The studies also provide evidence-based knowledge to the NBC standing committee to help it publish its illustrated user’s guides and address building code change requests. Overall, the goal is to protect Canadians from radon and provide solutions for radon-mitigation practitioners to achieve better results with a larger array of options.
Hans Schleibinger, PhD, is an environmental engineer who worked in the areas of air and water pollution control, prevention of mould growth, hospital hygiene, toxicology, and environmental analysis in Germany. He has headed the Ventilation and Indoor Air Quality Group of the National Research Council (NRC) since 2005, evaluating products and technological solutions for the building sector and creating evidence-based knowledge for Canadian stakeholders. Schleibinger was also one of the founders of the Canadian Committee on Indoor Air Quality and Buildings (CCIAQB). He can be reached vis e-mail at firstname.lastname@example.org.
Deepti Bijlani holds a master’s in microbiology from the University of Mumbai, India. She has been the senior radon project manager within Health Canada’s Radon Technical Operations group since 2010, and has been involved in various technical projects undertaken in collaboration with stakeholders under the National Radon Program. Bijlani currently manages several projects for the group, including two national radon mitigation standards in development. Prior to joining Health Canada, she worked for more than nine years in the biotechnology and pharmaceutical industry as a quality control and research microbiologist in the nuclear medicine field. Bijlani can be reached at email@example.com.
Liang Grace Zhou, PhD, earned her doctorate in building engineering at Concordia University, where she also completed projects for Public Works and Government Services Canada (PWGSC) to optimize building design for federal net-zero targets. She joined NRC as a research officer on the Ventilation and Indoor Air Quality Group in 2008, and led her team in developing one of Canada’s first and two of the world’s first radon test facilities, as well as completing research activities and product validations to control radon in buildings. Zhou can be reached at firstname.lastname@example.org.
Jeff Whyte holds degrees in chemistry and analytical chemistry. He is the head of the Radon Technical Operations group working on the National Radon Program at Health Canada’s Radiation Protection Bureau. Whyte has more than 30 years of experience in chemical and radiochemical research in the private and public sectors. He was a member of the Joint Task Group on Protection Against Radon Ingress for the 2010 National Building Code (NBC), and is the chair of the technical committee for two national radon mitigation standards under development. Whyte can be reached at email@example.com.
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