Difficult Crawlspaces

Crawlspaces under the living space of a home provide a are very large area through which radon laden soil gas can travel.  these are typically treated by installing a high density polyethylene sheet on the floor of the crawl space, sealing seams and the edges to the walls and drawing air out from beneath the plastic sheet.  These systems, referred to as sub-membrane depressurization systems are very effective in collecting radon and exhausting it to the atmosphere provided a worker can access the crawl space or there are no hazards within it the would prevent the use of this technique. the two most problematic cases associated with treating crawlspaces are:

• Inaccessible crawlspaces, where headroom does not allow access into the area to apply the plastic

• Presence of asbestos on plumbing or heating ductwork.

• Or both of the above, which is common since both conditions can be found in older homes.

Certainly one could dig out the crawl space, but that would be very expensive. 

One could also depressurize the crawlspace itself and exhaust radon and a significant amount of interior air to the atmosphere, but there are significant heating penalties or combustion appliance backdraft potentials associated with this and certainly not an option if asbestos is present.

One could also abate the asbestos, but typically this is very expensive and not warranted if the asbestos containing materials are in good condition or are not disturbed.

These are situations where a more thorough investigation of health risks using PGL's radon and radon decay product measurement devices would be appropriate.  This would be to either verify that mitigation is indeed warranted or if air filtration devices could reduce radon decay products as well as reduce airborne particulates, such as asbestos fibers and thereby improve other potential indoor air quality concerns.

The following are examples of where whole house air filtration systems have been employed.  Click on thumbnail photos to view pictures more clearly.

Air Filter Concept Air circulation created by filter increases plate-out of Radon Decay Products as well as particles to which they are attached.	Stand-alone Whole House Filters Separate fans and ductwork, operate separately from forced air unit or where no forced air system exists.	High Efficiency Filters for Forced Air Units Low pressure drop filters allow them to be added into the return ductwork.
Impact of Whole House Filter System (1) Radon is not affected but decay products are significnatly reduced.	Impact of Filter System (2)	Impact of Filter System (3) A follow-up measurement in house indicated radon decay products continued to be controlled.
Effect of Extreme HEPA This is in a laboratory setting where very high circulation rates existed and a very tight HEPA filter was used. This building was slotted for mitigation and interior vacuums were so high (-0.150 in H2O) that several ASD systems would have been needed.	Effect of Air Circulation Much of the radon decay product reduction comes from simple air circulation. Filters enhance reduction and beneficially remove other particulates.	Effect on Unattached Fraction Analogy Although the percentage of the total radon decay products in the small particle range can increase the overal exposure is reduced. See comment below from the National Academy of Sciences.

During the mid 1990s much of EPA's research budget into new mitigation strategies was reduced.  This occurred at a point in time that air filtration techniques were beginning to be studied, but not completely.  Consequently, some unanswered questions regarding the potential increased dose from the use of air filters in increasing the unattached fraction was placed in some documents and cast doubts on their use.  However, subsequent to this and with better instrumentation, researchers have shown that although the unattached fraction goes up and so does the dose per unit exposure increases, the overall exposure goes down sufficiently to compensate for this. 

This follow-up research was included in the US EPA driven research into risk assessment of waterborne radon and within the section where alternative mitigation techniques were reviewed and updated.

Risk Assessment of Radon in Drinking Water NATIONAL ACADEMY PRESS, Washington, D.C.
1999, Pages 149-151

“From the more recent studies on air cleaners and their effects on exposure to and dose from airborne radon decay products, several important conclusions can be drawn. With the new dosimetric models that more accurately reflect nasal and oral deposition of ultrafine particles, it is extremely unlikely that an air cleaner can reduce exposure and increase dose as suggested by Maher and others (1987), Sextro and others (1986), and Rudnick and others (1983). Thus, there is no reasonable likelihood that the use of an air cleaner will increase the hazards posed by indoor radon.”

 

 

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Last modified: 06/05/08