Radon, although a chemically inert gas, is an unstable atom. It will breakdown, or radioactively decay, into other elements. These elements, since they are derived from radon are called radon decay products. They have historically also been called radon progeny and radon daughters. The ones of greatest health risk concern are the short-lived radon decay products that release alpha energy. These are Polonium 218 and 214.

What is more hazardous, radon gas or radon decay products?

Actually it is the radon decay products that present the primary health risk associated with the presence of radon in indoor air. When radon is present in the room, its decay products will also exist. When you inhale, you inhale both the radon and the radon decay products. When you exhale, the radon is exhaled, but the radon decay products will remain in the lungs. That is because the radon decay products have electrostatic charges that cause them to adhere to lung tissue. Although the lungs can expel them through the normal clearing process, it takes a fair amount of time to do so and in that time frame the decay products themselves, will breakdown, releasing alpha radiation to the lung cells that the decays products are near.

In short, because the radon decay products have a longer residence time in the lungs, they pose the primary health risk of irradiation of the lung tissue.

Since radon emits alpha when it decays, can’t it also present a lung cancer risk?

Technically, there is some risk of increased lung cancer risk from breathing radon. However, the probability of a radon atom decaying at the instant it passes through the lungs and into the blood and back out (by the normal gas exchange process) is very low compared to the chances of a radon decay product decaying while in the lungs, since the radon decay products stick and accumulate in the lungs. The other factor is that radon has a much longer half-life of 3.8-days compared to Polonium 218 at 3.05 minutes and Polonium 214 at 164 micro-seconds, which means these short-lived radon decay products will likely breakdown and release radiation before your lungs can clear them.

Which represents a higher risk, radon or radon decay products?

Radon decay products present the higher risk for a given exposure (see above).

If radon decay products represent the health risk from radon exposure, why don’t we just measure the radon decay products?

There are several approved devices that measure radon decay products. In fact much of the historical research that links radon exposures to lung cancer were based upon the direct measurement of the dose causing radon decay products. Unfortunately, the measurement devices used for this more definitive measurement of risk were expensive and during the late 1980s it was desired that a less expensive device be made available for consumer measurements. This gave rise to the measurement of radon gas as a surrogate measurement for estimating radon decay product exposure.

Recent advances in technology have now made the direct measurement of radon decay products much more feasible and therefore allowing for a more definitive characterization of health risk.

How accurately do radon gas measurements alone estimate health risks from radon decay products?

Devices that measure radon gas alone, estimate the amount of radon decay products in the air by a simple equation that is based upon an assumption of what percentage of the radon decay products formed from a given amount of radon remain in the air and available for inhalation. Since, radon decay products have electrostatic charges, they will adhere to fixed objects (like the interior of ductwork, walls, floors etc.). Once they attach to these fixed objects, they are not dislodged with air currents, dusting etc. In other words, they no longer present a health risk.

In developing radon gas measurements as a means to estimate radon decay product exposure, the US EPA assumed that 50% of the decay products, formed from radon, remain in the air. However, this assumption can be highly variable from home to home, depending upon air movement, presence of filters (all of which reduce radon decay products in the air), or high levels of particulates in the air that provide sites to which the decay products can attach and stay suspended, such as the presence of outdoor air pollution, smoking in the house, etc.

In essence, a radon gas measurement only estimates potential levels for radon decay products in the home. The accuracy of this estimation depends upon the assumption of the distribution of decay products in air versus on fixed surfaces: In the case of buildings with low particulate levels and high air circulation a radon gas measurement will likely overestimate radon decay products exposures; and in the case of buildings with high particulate loading, a radon gas measurement will under-estimate the risk.

So which is better a radon gas measurement, or a radon decay product measurement?

Neither is better than the other because they measure two different things. A radon gas measurement provides an indication of the potential exposure, and a radon decay product device provides a measurement of the actual exposure. However, if a professional tester obtains a result where the radon is elevated, but the radon decay products are not elevated, they will look to see what is causing this situation. Perhaps it is because a forced air furnace or air conditioning system exists, or perhaps there is a whole-house filtration system or maybe the building is in an area where the outdoor air is relatively clean. If they determine there is a logical condition that is causing this much lowered risk from radon decay products and it is a condition that is likely to occur while the building is occupied, then they will make their recommendations on the basis of the radon decay product measurement, because it is the direct measurement of the dose causing radon decay products.

Why do PGL devices provide both radon and radon decay products?

We believe that it is important to know both the potential risk as well as the actual risk. By knowing both, and if a decision is made not to reduce radon gas levels because the radon decay products are low, then the client understands that if the conditions that are causing the reduced radon decay products are changed (such as removal air filtration systems) then the actual risk from radon decay products could increase due to the presence of elevated radon gas.

If the radon gas is elevated, but the radon decay products are below the EPA guidance, upon which should I base my decision to mitigate?

The EPA has two guidances, 4.0 pCi/L for radon gas as a surrogate measurement, and 0.02WL of radon decay products as the actual dose causing elements. If all considerations are equal, the measurement of the radon decay products provides a better indication of actual health risk and therefore a good basis for a decision. However, this should be balanced with the fact that if the conditions that are causing the lowered radon decay product levels change (such as a change in the furnace type, or a significant downturn in outdoor air quality occurs, or a presence of a smoker) that one should view the radon gas measurement as a potential exposure that could be present under less desirable circumstances. Remember that the use of a radon gas measurement alone, assumes 50% of the decay products are plated out on walls, and even this assumption can under estimate the risk in the presence of high levels of particulates in the air.

Do devices that reduce particulates in the air reduce radon exposure?

No. Mechanical air filters or electrostatic air filters do not reduce radon in the air. Radon is a chemically inert gas that cannot be mechanically filtered out of the air.

Do devices that reduce particulates in the air reduce radon decay product exposure?

Yes. Air filtration devices that circulate air within a building through a filter will significantly reduce radon decay products. This is caused by two effects. One is the increased air movement within the building facilitating the contact of airborne radon decay products with fixed objects to which they adhere (they cannot be re-suspended with additional air movement or cleaning). The other effect is that as air moves through the filters, the radon decay products will adhere to the filter media, or particles to which the radon decay products are attached will be collected by the filter.

If I install an air filter should I retest the building to insure the levels have been reduced?

Yes. As in any mitigation approach, one should always retest the building to verify reductions.

If I install an air filter, what type of test device should be used to verify reductions?

The only way to verify the proper operation of an air filter in reducing the health risks from the presence of radon is to test with a device that measures radon decay products. A radon gas measurement alone, will not provide an indication of effectiveness of these devices, since air filters do not reduce radon gas.

The best measurement method is to measure both the radon and the radon decay products to insure that the reduction in radon decay products is from the filter rather than from a temporary reduction in radon gas. That is why Progeny measurement devices provide for both measurements.

If I have my building tested with a radon decay product measurement device, how should it be retested in the future?

If you retest in the future, perhaps when it is resold, or to verify continued radon decay product reductions of a filter, you should retest with a device that measures radon decay products. A radon gas measurement device alone, will not show the benefits of reduced radon decay products.

Won’t the use of radon decay product measurement devices hurt the radon mitigation industry?

No, in fact it has proven to be a benefit to the industry.

Over the past 10 years, research by PGL staff has shown that the use of radon decay product measurements has been very helpful to mitigation contractors who have encountered buildings where traditional active soil depressurization methods have not been able to fully reduce radon to less than 4.0 pCi/L. Some of these situations have been where buried return ducts of forced air furnace systems overpower active soil depressurization systems, or there are crawl spaces that are inaccessible to where traditional sub-membrane depressurization systems cannot be installed. In some cases, a measurement of radon decay products indicate that radon decay products are below the EPA guidance after initial mitigation techniques have been applied, or the simple change-out of air filters type will reduce the exposure down to acceptable levels.

The increased availability of radon decay product measurement devices will also provide an additional mitigation technique, i.e. air filtration, that can provide an alternative to active soil depressurization that also provides benefits to building occupants.

The re-emergence of radon decay product measurement devices provide for the use of alternative mitigation techniques and approaches that broaden the services and tools of mitigation contractor, and also provides a means where they can expand into indoor air quality. In other words, radon decay product measurement allows for another arrow in the quiver.

Are radon decay product measurements variable over time?

If a short-term test is conducted (2-3 days in duration) in accordance with EPA protocols, the result will be indicative of the conditions that existed at the time of the test. Certainly conditions that effect radon entry can be different from season to season, even though short-term testing conditions of all exterior doors and windows being closed serves to force the radon entry levels up, they can still vary. The best measure of exposure is a long-term test, lasting for a minimum of 91 days up to a full year under normal lived-in conditions. PGL now offers a long-term radon and radon decay product test device, for further assurance of radon decay product exposures.

In essence, radon decay product levels can vary since the radon entry can vary, but radon decay product measurements (either short or long-term) provide the best characterization of actual risk.

Can radon decay product levels spike with certain activities?

Yes. If radon gas levels are constant and an activity like smoking in the house or letting smoke from a fireplace spill into a room, there can be a sharp increase in the radon decay products suspended in the air. This is because the radon decay products will attach to these particles rather than preferentially be plated out on the walls, where they would no longer represent a risk. Even when this occurs, the radon decay products typically only go up to an equilibrium fraction of 50% (EPA’s assumption). However, when the condition that caused the high particulate levels in the indoor air is corrected, the radon decay product levels quickly diminish to lower levels (within an hour). So bottom line, if you are concerned about risks from radon, don’t smoke in the house (or don’t smoke at all) and keep the air in your house free from high particulate levels. Note this is also where air filters can be a large help.

Are there methods for conducting long-term radon decay product measurements?

Yes, Progeny has developed the means by which one can measure both radon and radon decay products on a long-term basis using passive detection devices. These devices are currently undergoing final review and will be available beginning February 15, 2005.

What is the Equilibrium Equivalent Radon?

Equilibrium Equivalent Radon, or EER, is the amount of radon gas that would be needed to create the amount of radon decay products that were measured, assuming 50% of the decay products created are in the air.

Converting radon decay product measurements from Working Levels (WL) to an equivalent amount of radon gas is a convenient way to compare the radon decay product measurements to the sometimes more familiar EPA guidance of radon which is 4.0 pCi/L.

The radon decay product measurement can be compared to the EPA guidance of 0.02WL or this measurement calculated in terms of EER can be compared to the EPA Guidance of 4.0 pCi/L.

Where did the US EPA guidance of 4.0 pCi/L come from?

Although this question could be answered with volumes of statistics. The 4.0 pCi/L guidance was based upon a standard of 0.02Working levels (WL) of radon decay products, for clean-up actions under the purview of the US EPA (see 40 CFR Part 192.12(b)). Using a 50% equilibrium factor which is the assumption that 50% of radon decay products produced remain in the air, a level of radon gas needed to produce 0.02WL can be calculated, which is 4.0 pCi/L of radon.

The advantage of Progeny measurement devices is that an assumption like 50% is not necessary, since they measure the dose causing radon decay products directly, as well as provide the actual radon gas measurement.

Are Radon and Radon Decay product measurements more expensive than radon gas measurements alone?

Yes, they are slightly more expensive. This is because there are two separate measurements being conducted. But the extra cost is well worth the additional information provided to more fully characterize the health risk, which can save a tremendous amount of money in avoiding unnecessary mitigation costs or by better reducing your liability as a seller or financial institution.

Send mail to Progenyltd@aol.com with questions or comments about this web site. Copyright © 2004 Progeny Group, Ltd. Last modified: 06/05/08

Send mail to Progenyltd@aol.com with questions or comments about this web site.
Copyright © 2004 Progeny Group, Ltd.
Last modified: 06/05/08