7 Steps of Radon Prevention Strategies (Part 2)
Posted on April 29th, 2010 in Inner Healing At Home Pollution, Radon
(continue from 7 Steps of Radon Prevention Strategies – Part 2)
C. Sealing of Surfaces
The sealing of the surfaces which separate the indoor occupied space from the soil can improve the performance of other prevention strategies such as PSD or ASD. In these cases, sealing reduces the loss of conditioned air from indoors, which may be substantial, and increases the reversal of air pressure from the soil to the indoors.
As a stand-alone prevention strategy, sealing has limited potential for radon reduction, especially over time. Sealing does not address the major reason why radon moves from the soil to the indoors, i.e. pressure-driven airflow.
D. Barriers and Membranes
Barriers or membranes between the soil and the indoors may be used as a stand-alone radon prevention strategy or in combination with other techniques such as passive or active soil depressurization. Membranes may also help limit moisture migration to the indoors. Consideration should be given to using barriers with independent third-party approval for characteristics such as air tightness, diffusion, strength and durability properties.
While barriers may be useful to reduce radon transport from the soil to the indoors, opinions vary about their effectiveness:
- installed, while acknowledging that the barrier must be air-tight. Scivyer and Noonan (2001) found in their study that there were no significant changes in radon concentrations in homes with full radon membranes over a ten-year period. However, there was no indication concerning the initial effectiveness of the membranes;
- air-tight under common construction conditions. A punctured membrane would potentially act as a trap to collect soil gas and funnel it into the building through any available openings. In addition, barriers do not address air pressure differences. Barriers might be more effective in moderate climates where pressure differences due to temperature are small.
Barriers may be used in combination with other prevention techniques such as soil depressurization. When used with soil depressurization, the barrier does not need to be continuous. For example, in Finland, when soil depressurization piping is installed, reinforced bitumen felt is installed below the floor-foundation wall.
E. Ventilation of Unoccupied Spaces
Ventilation of unoccupied spaces between the soil and the occupied space (e.g. vented crawlspaces) can reduce indoor radon concentrations by separating the indoors from the soil and reducing the concentration of radon below the occupied space. The effectiveness of this strategy depends upon a number of factors. These include the air-tightness of the floor system above the vented unoccupied space, and, with passive ventilation, the distribution of vents around the perimeter of unoccupied space.
A variation of this approach involves the use of a fan to either pressurize or depressurize the unoccupied space. However, fan-driven depressurization of crawlspaces may pose problems such as back-drafting of combustion appliances and energy loss. Subslab and Submembrane depressurization (SSD and SMD) may be either active or passive and are recommended for radon control in buildings with crawlspace foundations. SSD and SMD offer greater radon reduction than crawlspace ventilation.
Basement suction, 4 inch PVC pipe. Sub-slab depressurization systems require a suction point installed through the concrete floor and piped to a fan located outdoors or in an attic space. Image is taken from www.highlandair.org
F. Ventilation of Occupied Spaces
For overall indoor air quality, an exchange between indoor and outdoor air is desirable. For radon prevention, ventilation has varied results and may lead to energy losses, especially in extreme climates. If the major radon source is building material, ventilation will be needed. However, it is better to avoid the use of building materials that are sources of radon in the first place (EC 1999).
G. Water Treatment
Water treatment is not commonly carried out in new constructions, except in areas where high radon concentrations in water are known to be a problem. In the relatively rare cases where significant amounts of radon are transported indoors by water from a private drilled well, radon is released into the indoor air. In such cases, water treatment may be used to reduce the indoor air concentration of radon. The health risk associated with radon in water is primarily via inhalation as opposed to ingestion.
The primary strategies to reduce indoor radon from well water at the point of entry into the home are:
- is sprayed into the air or is cascaded over objects while radon is extracted from the water to the outdoors;
- results in less radon reduction.
GAC is also effective in removing radon from water, with removals of 70–100% (Lykins et al., 1992). The amount of radon removed by activated carbon is effectively unlimited, because the adsorbed radon decays into other radioactive products, such as 210 Pb. As the adsorbed radon decays, radioactive progeny emitting gamma radiation is produced, possibly creating a disposal problem (Castle, 1988). Elevated gamma dose rates (up to 120 mSv/h) near the filter have been recorded (Annanmäki & Turtiainen, 2000). Screening of the GAC filter could be required. In some circumstances, a twin tank system, which introduces a time delay that allows the radon to decay to a significant extent, may be a low-cost option.
Dembek et al. (1993) and the WHO Guidelines for drinking water (WHO 2005) give further information on radon mitigation in water.
Hope this will be much helpful.
Related posts:
- 7 Steps of Radon Prevention Strategies (Part 1)
- Radon, Searching For The Cracks In The Wall
- Why Is There Radon In My House? Where Does This Thing Come From?
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