Radiation and Granite Counters
If you are concerned about the radiation risk to you and your family in your home, the first thing to do is perform a radon test. Radon is the primary cause of lung cancer among non-smokers and is the second leading cause of lung cancer after smoking. Radon at the average indoor level of 1.3 pCi/l constitutes the single largest source of radiation exposure for the average American. Radon comes from the radioactive breakdown of naturally occurring radium found in most Florida soils, and in most earthen material used in the building process. In the vast majority of buildings with radon problems, the largest source of radon is soil gas entering the building through small openings in the foundation. Since any building has a limited volume of air, indoor radon concentrations can be many times that of outdoor air, about 0.4 pCi/l. Radon testing can be a simple first step for determining if there is any chance that the granite in your home could be a significant radiation risk. If you perform a radon test and the radon level is low, then the likelihood of there being a significant amount of radiation emanation from your countertops is extremely low. To test for radon, you can use radon test kits from your local home improvement store or internet retailers, or you may contact a State of Florida certified measurement business. If you use a home test kit, only use a kit listed with either the National Radon Proficiency Program or the National Radon Safety Board. Follow the testing procedures in the US EPA's "A Citizen's Guide to Radon" and mitigate for elevated radon if appropriate. There have been thousands of radon mitigations in Florida. Never has a Florida radon mitigation required that a granite counter top be removed to protect the home occupants.
With the concern over the radioactive risk potential of granite countertops, it is important to remember that we are always exposed to a certain level of background radiation. All granite, and most earthen materials, contain trace amounts of uranium and radium, emit gamma radiation and release radon gas. While the Florida Department of Health has never performed a study specifically designed to evaluate any health risks of granite counter tops, staff from the Florida Department of Health's (DOH) Bureau of Radiation Control and from DOH's Radon Program have had the opportunity over the years to survey various granite samples for gamma emissions, including a few granite counter tops, and have yet to find granite to be a significant gamma radiation hazard. The term 'significant' is used because there is measurable gamma radiation from granite as radiation is always around us, just not at levels of concern.
If you still wish to have your granite counter tops evaluated for their potential for radiation exposure, please be aware there are no state or federal standards for analysis or the professionals performing the service. Evaluating the gamma radiation and radon emanations from the granite are two separate steps that may require different specialists with slightly different knowledge sets and experience. Should the professional make a determination of your risk from radon, provide radon in air measurement services, make recommendations on strategies to reduce radon levels, they must be certified by this office.
The gamma radiation exposure evaluation would start with a survey performed with a dose rate meter. This is a device that evaluates not only the rate of radioactivity, but the energies of the gamma photons. The individual performing the survey would then need to be able to evaluate the measured dose rates against occupancy and use patterns in the area to determine an estimated annual exposure. While there are no radiation exposure standard standards specific to granite counter tops, there are two standards that may be referenced in any professional evaluation:
1) There is general guidance on radiation exposures in buildings and radiation exposure from naturally occurring radioactive materials. Chapter 64E-5.1001 of the Florida Administrative Code recommends that the mean gamma exposure rate in a building should not exceed 20 micro roentgens per hour including the background. This standard allows for localized areas in the building to have a higher gamma exposure rate provided that the overall mean does not exceed the standard. There is no guidance on how to interpret or implement this standard. Whether it should be calculated based on actual occupancy and usage patterns or as a simple average across the entire building space.
2) The Nuclear Regulatory Commission has a public dose limit due to licensed activities of 100 mrem/year. This is a dose above the average person's exposure of 360 mrem/year. This standard has been used in proposed standards for exposures to the public from naturally occurring radioactive materials.
Evaluating the radon producing potential of any material involves the evaluation of how much radon comes out of the surface per unit time. The technique used is often referred to as a 'radon flux' or 'flux bucket' measurement. A container of a known volume of air is sealed to the surface to be measured for a set period of time. A radon testing device is used to measure the change in concentration of radon in the container. A calculation must then be applied to evaluate the contribution from the radon in the container to the entire volume of air in the building. In Florida, the department certifies persons who perform radon gas or radon progeny measurements, including sample collection, analysis, or interpretation of such measurements. Most of the state certified professionals only have experience in radon for indoor air measurements. You may need to ensure that the radon measurement specialist of the radon testing company has reviewed and approved any procedures related to the radon emanation measurements.