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Radon mitigation is any process used to reduce radon concentrations in the breathing zones of occupied buildings. Mitigation of radon in the air is accomplished through ventilation, either collected below a concrete floor slab or membrane on the ground, or by increasing the air changes per hour in the building. Treatment systems are available to remove radon from domestic water supplies.
The first step in mitigation is testing to see if the indoor-air and/or domestic water radon concentrations should be reduced. No level of radiation is considered completely safe but it cannot be totally eliminated so governments around the world have set action levels to provide guidance on when radon concentrations should be reduced while recognizing that radon cannot be eliminated. Radon in the air is considered to be a larger health threat than radon in domestic water.
Air-radon levels fluctuate naturally on a daily and seasonal basis. A short term test (90 days or less) might not be an accurate assessment of a home's average radon level, but are recommended for initial testing to quickly determine unhealthy conditions. Transient weather such as wind and changes in barometric pressure can affect short-term concentrations as well as ventilation such as open windows and the operation of exhaust fans.
Testing for radon in the air is accomplished using passive or active devices placed in the building. Some devices are promptly sent to a laboratory for analysis, others calculate the results on-site. Radon-in-water testing requires a water sample being sent to a laboratory.
Retesting is recommended in several situations such as to double check test results before spending money on the installation of a mitigation system. Test results which exceed accuracy tolerances also require re-testing. When a mitigation system installation is warranted, a retest after the system is functional is advised to be sure the system is effectively reducing the radon concentration below the action level, and after any mitigation system repairs such as replacing a fan unit. Retesting is also recommended every ten years.
Testing in the United States
ASTM E-2121 is a US standard for reducing air-born radon in homes as far as practicable below the action level of 4 picocuries per liter (pCi/L) (148 Bq/m3).  Some states recommend achieving 2.0 pCi/L or less.
Radon test kits are commercially available and can be used by homeowners, tenants and in limited cases by landlords, except when a property is for sale. Radon testing at the time of a real estate transaction or in larger, more complicated buildings such as schools and multi-unit apartment buildings must be completed by qualified, certified measurement service providers.
Commercially available test kits includes a passive collector that the user places in the lowest livable floor of the house for 2 to 7 days. The user then sends the collector to a laboratory for analysis. Long-term kits, taking collections from 91 days to one year, are also available. An open land test kit can test radon emissions from the land before construction begins, but are not recommended by the EPA because they do not accurately predict the final indoor radon level. The EPA and the National Environmental Health Association have identified 15 types of radon test devices. A Lucas cell is one type of device.
Retesting is specifically recommended in several situations. Measurements between 4 and 10 pCi/L (148 and 370 Bq/m3) warrant a follow-up short term or long-term radon test before mitigation. Measurements over 10 pCi/L (370 Bq/m3) warrant only another short-term test (not a long term test) so that abatement measures are not unduly delayed.
Purchasers of real estate may delay or decline a purchase if the seller has not successfully abated radon to less than 4 pCi/L.
Management of radon service provider certification has evolved since being introduced by the EPA in 1986. In the 1990's this service was "privatized" and the National Environmental Health Association (NEHA) helped transition the voluntary National Radon Proficiency Program (NRPP) to be administered by private firms. As of 2012 the NRPP is administered by the American Association of Radon Scientists and Technologists (AARST).
Testing in Canada
Canadian Government, in conjunction with the territories and provinces, developed the guideline to indicate when remedial action should be taken was originally set at 800 Bq/m³ (becquerels per cubic meter) and since reduced to 200 Bq/m³. This new guideline of was approved by the Federal Provincial Territorial Radiation Protection Committee in October 2006.
Methods of mitigation
Because high levels of radon have been found in every state of the United States, testing for radon and installing radon mitigation systems has become a specialized industry in the last two decades. Many states have implemented programs that affect home buying and awareness in the real estate community, however radon testing and mitigation systems are not generally mandatory unless specified by the local jurisdiction.
According to the EPA's "A Citizen's Guide to Radon", the method to reduce radon "primarily used is a vent pipe system and fan, which pulls radon from beneath the house and vents it to the outside", which is also called sub-slab depressurization, active soil depressurization, or soil suction. Generally indoor radon can be mitigated by sub-slab depressurization and exhausting such radon-laden air to the outdoors, away from windows and other building openings. "EPA generally recommends methods which prevent the entry of radon. Soil suction, for example, prevents radon from entering your home by drawing the radon from below the home and venting it through a pipe, or pipes, to the air above the home where it is quickly diluted" and "EPA does not recommend the use of sealing alone to reduce radon because, by itself, sealing has not been shown to lower radon levels significantly or consistently" according to the EPA's "Consumer's Guide to Radon Reduction: How to fix your home". Ventilation systems can utilize a heat exchanger or energy recovery ventilator to recover part of the energy otherwise lost in the process of exchanging air with the outside. For crawlspaces, the EPA states, "An effective method to reduce radon levels in crawlspace homes involves covering the earth floor with a high-density plastic sheet. A vent pipe and fan are used to draw the radon from under the sheet and vent it to the outdoors. This form of soil suction is called submembrane suction, and when properly applied is the most effective way to reduce radon levels in crawlspace homes."
The most common approaches are active soil depressurization (ASD) and mechanical ventilation (MV). Experience has shown that ASD is applicable to most buildings since radon usually enters from the soil and rock underneath and MV is used when the indoor radon is emitted from the building materials. A less common approach works efficiently by reducing air pressures within cavities of exterior and demising walls where radon emitting from building materials, most often concrete blocks, collects.
- Above slab air pressure differential barrier technology (ASAPDB) requires that the interior pressure envelope, most often drywall, as well as all ductwork for air conditioning systems, be made as airtight as possible. A small blower, often no more than 15 cubic feet per minute (0.7 l/s) may then extract the radon-laden air from these cavities and exhaust it to the out of doors. With well-sealed HVAC ducts, very small negative pressures, perhaps as little as 0.5 pascal (0.00007 psi), will prevent the entry of highly radon-laden wall cavity air from entering into the breathing zone. Such ASAPDB technology is often the best radon mitigation choice for high-rise condominiums as it does not increase indoor humidity loads in hot humid climates, and it can also work well to prevent mold growth in exterior walls in heating climates.
- In hot, humid climates, heat recovery ventilators (HRV) as well as energy recovery ventilators (ERV) have a record of increasing indoor relative humidity and dehumidification demands on air conditioning systems. It is very clear that serious mold problems have originated in homes that have been radon mitigated with HRV and ERV installations in hot, humid climates. HRVs and ERVs have an excellent record in heating climates.
- A recent technology is based on building science. It includes a variable rate mechanical ventilation system that prevents indoor relative humidity from rising above a preset level such as 50% which is currently suggested by the U.S. Environmental Protection Agency and others as an upper limit for the prevention of mold. It has proven to be especially effective in hot, humid climates. It controls the air delivery rate so that the air conditioner is never overloaded with more moisture than it can effectively remove from the indoor air.
- It is generally assumed that air conditioner operation will remove excess moisture from the air in the breathing zone, but it is important to note that just because the air conditioner cools does not mean that it is also dehumdifying. If delta t is 14 degrees or less, it may not dehumidify at all even though it is cooling.
- Factors that are likely to aggravate indoor humidity problems from mechanical ventilation–based radon installations are as follows and an expert radon mitigator/building scientist will check for and correct any and all of the following when he or she performs radon mitigation procedures:
- Air conditioner duct leaks located outside the breathing zone, such as in the attic.
- Excessive exhaust fan operation
- Oversize or over-capacity air conditioners
- AC air handler fans that do not stop running when the air conditioner compressor stops running.
- Delta t (Δt), which is the amount that the air is cooled as it is passed through the air conditioner's cooling coils. A good delta t performance figure for home air conditioners is about 20 °F (11 °C). In comparison, automobile air conditioners deliver Δt performance of 32 to 38 °F (18 to 21 °C). A delta t of 14 °F (8 °C) will dehumidify poorly if at all.
In South Florida, most all radon mitigation is performed by use of fixed rate mechanical ventilation. Radon mitigation training in Florida does not include any segment addressing mechanical ventilation or of problems associated with mechanical ventilation systems such as high indoor humidity, mold, moldy odors, property damage or health consequences of human occupation in high humidity of moldy environments. As a result, most Florida radon mitigators are unaware of and do not incorporate existing building science moisture management technology into mechanical ventilation radon installations.
Home inspectors are generally unaware of the mold risks associated with radon mitigation by mechanical ventilation even though mold may make occupants sick, destroy their home and property, and/or be very expensive to clean up and then make the home difficult to sell. In Florida the lawsuits are just beginning.
- "You've found radon in your home—what should you do?". Air Chek, Inc. Archived from the original on 2007-12-24. Retrieved 2008-02-02.
- "Recommended Residential Radon Mitigation Standard of Practice". United States Environmental Protection Agency. Archived from the original on 2008-01-16. Retrieved 2008-02-02.
- "ASTM E2121-03 Standard Practice for Installing Radon Mitigation Systems in Existing Low-Rise Residential Buildings". ASTM International. Retrieved 2008-02-02.
- "Commercially Available Radon Kits". Alpha Energy Labs. Retrieved 2012-04-19.
- "Radon Measurement Method Definitions". The National Environmental Health Association—National Radon Proficiency Program. Retrieved 2008-02-02.
- "NEHA and NEHA-NRPP History" http://www.nrpp.info/history.shtml accessed 1/24/2015
- The Canadian Guideline for Radon Control
- http://www.hc-sc.gc.ca/ewh-semt/radiation/radon/faq_fq-eng.php#reaction accessed 1/24/2015
- "Radon: Myth vs Fact". Radon-Rid/EPA. Retrieved 2009-11-13.
- "Listing of States and Jurisdictions with RRNC Codes". EPA. Retrieved 2009-11-13.
- "A Citizen's Guide to Radon". EPA. Retrieved 2010-04-03.
- "Radon Mitigation Methods". Radon Solution. Retrieved 2008-12-02.
- "Consumer's Guide to Radon Reduction: How to fix your home". EPA. Retrieved 2010-04-03.
- Radon at the United States Environmental Protection Agency
- Frequently Asked Questions About Radon ***Link needs updating. Page not found at site.*** at National Safety Council
- National Radon Program Services hosted by Kansas State University
- Home Buyer's and Seller's Guide to Radon An article by the International Association of Certified Home Inspectors (InterNACHI)
- Radon and Lung Health from the American Lung Association
- It's Your Health - Health Canada
- Radon's impact on your health – Quebec Lung Association
- World Radon Solutions Database is an information and experience exchange platform as to the different methods that exist to reduce radon in buildings
- Map referring to radon properties in England and Wales
- Citizens Guide to Radon
- EPA Federal Radon Mitigation Action Plan