Table 2.
Comparing effectiveness of different radon remediation methods in existing houses.
| Systems | Methods | Effectiveness |
|---|---|---|
| 1. Depressurization | ||
| a) Sub-slab depressurization (SSDS) | Vent pipes made of polyvinyl chloride are placed into the soil underneath the foundation. Air containing radon moving through the pipes is exhausted actively exterior to the building with an exhaust fan set at the garage, outdoors, or in the attic. | The most effective radon mitigation recorded in Calgary, Canada (Stanley et al., 2017) was 97.5%; previously the effects noted in Quebec by Brossard et al. (2015) was 95%. Whereas in the USA (Boardman and Glass, 2015) the highest record was 96.5%. In Austria, radon mitigation using the same methods with active and passive ventilation system shown 90% and 50% effect respectively (Maringer et al., 2001) |
| b) Sump depressurization | A form of SSDS, where the sump pump used to drain water is capped and made to serve as a passage to move out radon containing air. | Effectiveness recorded in both Spain (Vázquez et al., 2011) and in the UK was almost perfect (99 to nearly 100%) with active ventilation (Groves-Kirkby et al., 2006). |
| c) Sub-membrane depressurization | A polyethylene barrier membrane used to cover the dirt floor at crawl space; thus, the sealed foundation prevents radon entry. A vent pipe is placed in the crawl space to draw radon-containing air and exhausted with the aid of a fan to the outside. | Effectiveness noted was 53% only with the membrane but once an active vent pipe depressurization added with the exhaust fan; effectiveness raised to 98% in the UK (Scivyer, 2001). Studies in Austria, the USA, Hong Kong and the UK supported these findings (Ennemoser et al., 1995; Henschel, 1994; Gao et al., 2008; Scivyer, 1993). |
| d) Block wall suction, another type of SSDS. | Fan and ductwork used to draw suction on the hollow interior cavities of a concrete block wall. It keeps the inner air pressure lower than that in outside; thus, draws radon gas from the soil and expel out before entering the house. | Studies in Austria found 50–99% effect in radon reduction with the block wall suction (Ennemoser et al., 1995) |
| 2. Ventilation | ||
| a) Active Ventilation | With an active air exchange (by fan, air conditioning, heat recovery ventilators) indoor-outdoor pressure gradient is created. | Moderate effectiveness (25–75%) noted in the USA (Henschel, 1994), UK (Groves-Kirkby et al., 2008; Marley and Phillips, 2001; Naismith et al., 1998; Wang and Ward, 1997), and Norway (Rydock et al., 2002). |
| b) Passive ventilation | Air exchange between indoor and outdoor is increased by keeping the windows and doors open. | In Finland, passive ventilation is considered when winter radon level remains <400 Bq/m3 (Valmari et al., 2014). Less effective results with variability noted in the USA (Henschel, 1994) and Australia (Huber et al., 2001). |
| 3. Other | ||
| Filtration: HEPA (high efficiency particulate air) filter and HEPA with deodorizing activated carbon-filter | Both filtration methods (HEPA and carbon filters) act as air cleaner and can filter out radon progenies that are measured as a decrease in radon equilibrium equivalent concentration (EEC). In the control case, the experiment was conducted without using the air cleaner. | In Japan, the calculated effectiveness of decrease in radon EEC found significantly (p <0.01) lower with both filters compared to the control cases; though health risk remained unclear due to the increase in unattached radon EEC fraction (Yasuoka et al., 2009). |
| Mechanical supply and exhaust ventilation (MSEV) with heat recovery compared with Mechanical exhaust ventilation (MEV) & Natural ventilation (NV) | In Finland, impact of ventilation on the indoor radon level was assessed through an analysis taking into account the height and volume of the house, natural pressure difference, infiltration and mechanical ventilation rate noted in houses with NAV, MEV and MSEV strategies. | Regression analyses of radon concentrations with these strategies showed MSEV to markedly reduce pressure differences and radon concentrations by 30% in typically airtight apartments compared to the MEV and NV. They also noted radon concentrations 30 % lower in the two-story houses than in single units (Arvela et al., 2014). |
| a) Sealing (alone) | Sealing of radon entry points in floors and walls of buildings by impermeable filler and sealants | Least effects (0–40%) noted in the UK (Naismith et al., 1998), USA (Henschel, 1994) and Finland (Arvela, 2001). |