The Use of Air Cleaning Systems to Reduce Radon Related Health Risks
Speaker: Douglas L Kladder, BSChE
Level of Knowledge: Multi-Level
An increased recognition of indoor air cleaners has led to more frequent use of air cleaners, either as stand-alone units or as integral parts of central air handling systems. The primary health risk associated with radon is its decay products, which are electrostatically charged and readily adhere to dust particles. The use of air filters (provided these systems are properly designed and consistently operated) can be used to reduce radon related risks as well as other indoor air quality concerns. This paper will discuss a number of case studies where air filters were used to successfully treat radon decay products, especially in situations where conventional radon mitigation is not as effective as desired.
Indoor radon is considered to be a significant environmental hazard. This has led to the growth of several state and federal programs that serve to recommend that individuals not have long-term exposures to more that the US EPA’s guidance of 4.0 pCi/L. However, it is the radon decay products (RDPs) that cause the damage to lung tissue rather than their radon gas predecessor.
Radon mitigation approaches typically utilize active soil depressurization to collect radon gas prior to entry into a structure. This technique is typically very reliable, but occasionally can be difficult to implement, especially in large buildings such as schools or homes where foundations are complex. In these difficult cases, or where occupants could benefit from reduced particulate levels, air cleaning systems can be employed to reduce RDP levels-even though the radon gas may not be affected.
RDPs when created when radon gas radioactively decays are highly charged which causes them to attach to airborne particulates or fixed surfaces such as walls or the interior of air circulation ducts. Typically, it has been assumed that 40-50% of decay products remain in the air for inhalation. It is this assumed relationships that allows radon gas measurements to be used as a surrogate indicator of the actual health risk exposure that would be obtained if radon decay products were measured directly.
Devices that filter out suspended particles also filter out RDPs that are attached to those particles. This filtration action, when combined with internal air circulation, can reduce RDPs by as much as 90%.
Although impractical several years ago, the advent of whole building filtration units and special filters to reduce allergens and asthma triggers now make the use of air cleaners RDPs a viable approach for reducing RDPs. This is especially true when occupants value indoor air quality from air cleaning or when traditional mitigation approaches do not prove to be viable or successful.