• Measurement of Radon Decay Products
• Equilibrium Ratios
• Factors Affecting Equilibrium Ratios
• Illustration of Equilibrium Ratios
• Working Level Measurements
  (Testing for Radon Decay Products)
• CVC Offers WL Tests

Measurement of Radon Decay Products
Although radon testing has become more and more common throughout the United States and other countries, especially for homes, office buildings, and schools, and one routinely compares the results to a guideline of 4.0 pCi/L, it is important to note that the actual health risk comes from the short-lived decay products of radon – referred to as Radon Decay Products.

The measurement of radon decay products was the primary methodology used during the 1960’s to mid 1980’s as a means to monitor employee exposures in underground mines, and was the basis for clean-up efforts in certain western states where uranium mill tailings had inappropriately been used for building materials.
In determining compliance of these clean-up efforts, fairly intricate measurement equipment was used that actively took air samples and measured the activity of the particulates collected from the air.

Radon decay product measurements are expressed in units of Working Levels (WL) and exposure in terms of a time weighted average referred to as Working Level Months (WLM).

The correlation of actual exposure to radon decay products (WLM) to the incidence of lung cancer is the basis of the health studies from uranium miner exposures that form the foundation of EPA’s recommendations and OSHA regulations, of an action level of .02 WL.

Upon discovery that the health risks of radon was more prevalent than in mines and from uranium mill tailings, and in fact could be found in many homes throughout the United States, research was initiated to identify measurement methods that could more easily estimate radon decay product concentrations. It was found that measuring radon and estimating the amount of radon decay products was a more cost-effective and easier method of testing.

In order to relate the measurement of radon to an equivalent amount of radon decay products, it was necessary to assume a ratio of the amount of radon decay products that are produced and available for inhalation from the amount of radon in the air.

Equilibrium Ratio

This assumption (called the equilibrium ratio) came about from extensive research and statistics available at the time. The assumption of 50%, which is used today, was based upon residential structures with average air recirculation rates, with a typical range of suspended radon decay products at 30% to 70%.

This assumed equilibrium rate of 50% equates to .02 WL measurements (the EPA established "action level.")

Factors Affecting the Equilibrium Ratio
It is well known that increased air movement causes more of the hazardous radon decay products to adhere to fixed objects (they do not detach once in contact with an object), thus, decreasing the amount of radon decay products available for inhalation – and decreasing the equilibrium ratio.

For instance, it has been found that buildings where large airflows or HEPA filters exist, the percentage of airborne radon decay products can be considerably lower.
 

Illustration of Equilibrium Ratio

In this example, when the equilibrium ratio is actually 30%, and assuming the radon levels were 4.0 pCi/L, the actual radon decay products (health risk) would be .01 (less than the action level of .02):

Radon = WL x 100/ 0.5 (Equil Ratio)
4.0 (radon) = .01(radon decay products) x 100 / 0.3 (Equilibrium Ratio)

Working Level Tests - Testing for Radon Decay Products
Testing for Radon Decay Products is now more accessible with more Working Level Test Devices available (see WL Device Report). Although typically more expensive than a radon test, it can be a very cost-effective option for homeowners where radon test results indicated a reading of 4-10 pCi/L, or where the ventilation system of the home creates increased air movement.

This is also very often the most cost-effective method of testing for large buildings, or homes in which a mitigation system would be extensive.

Using a WL meter for testing would not only give a better idea of radiation exposure it could show that a house that tests above the action level of 4 pCi/L may very well be below the 0.02WL guidance. This could provide great savings by eliminating a radon mitigation system.

CASE STUDY:

The graph above was developed from data collected on both radon and radon decay products in a building where initial radon measurements indicated a potential concern.

The upper line represents the radon that was measured and was clearly above the US EPA action level of 4.0 pCi/L. However, the radon decay products were less than the 0.02 WL action level.

The lower radon decay product concentrations was due to the effects of the air handling system in this large building that operated continuously during occupation.

Results:
This clearly indicated that the risk was lower than expected and an expensive mitigation of this hotel was avoided.

CVC has the equipment and Personnel to Offer WL Testing
The only way to know if radon decay products are being beneficially reduced is to use special equipment and qualified operators.

Colorado Vintage Companies has the equipment and personnel to offer testing for RDPs as well as traditional types of radon testing.

Our personnel are NEHA certified for all the methods of testing it performs.

            To contact us:

Colorado Vintage Companies, Inc.
525 E Fountain Blvd; Colorado Springs, CO  80903
Phone:  719-632-1215; Fax:  719-632-9607
Email:  coloradovintage@aol.com

Last modified: 06/04/04