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Radon

Radon. Introduction. Radon is a colorless and odorless gas produced by the decay of radium – 226 Radon after decay produces radioisotopes known as radon daughters Radon progenies (Po-218 and Po-214) are of health concern, as they tend to retain in the lungs causing cancer

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Radon

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  1. Radon

  2. Introduction • Radon is a colorless and odorless gas produced by the decay of radium – 226 • Radon after decay produces radioisotopes known as radon daughters • Radon progenies (Po-218 and Po-214) are of health concern, as they tend to retain in the lungs causing cancer • The upper limit recommended by US EPA for radon is 4pCi/L • Radon is found in many states in the USA

  3. Sources

  4. Sources of Radon • Sources of radon include • Soil • Rocks beneath or surrounding the building • Water • Building materials • Natural gas • Radon from soil moves slowly from the pores of the soil to the surface by diffusion or pressure induced flow • Radon enters the building from the cracks and joints in the foundation

  5. Effective radon (Rn - 222) Content of Soils

  6. Factors affecting transport of Radon to the surface • Soil permeability • Porosity • Water content • Temperature • Pressure difference between soil and building structure

  7. Permeability of Soils

  8. Sources of Radon • Water is also one of the potential sources due to high solubility of radon • The transfer of radon from water to air decides its contribution to the indoor concentration • Building materials like granite, clay bricks, marble and sandstone are also sources of radon • Fly ash from coal-fired power plant is a major source of radon, which is used in concrete and cement

  9. Sampling and Measurement

  10. Sampling Methods • Radon is measured indoors by the detection of alpha, beta or gamma emissions during the decay • The sampling methods are classified as: • Grab sampling • The study is conducted for a short period indoors by using scintillating flask • This method is advantageous in sensitivity and rapidity but is less accurate • When concentration is less than 10 Bq / m³ the error is more than 30%

  11. Sampling Methods • Continuous sampling • This method gives a real time measurement at short interval over a long time • The devices available for this type are: • Flow through scintillating chamber (two-port Lucas cell) • Solid state detector (wrenn chambers) • The wrenn chamber is the most widely used device capable of measuring concentrations even below 10Bq/m³

  12. Integrated Sampling • The devices used in this technique are: • Alpha tract detectors • Electronic ion detectors • Charcoal canisters • The charcoal canister method is EPA recommended and widely used method • This is easy to use and can be sent through mail to lab for analysis • The disadvantage of this method is an assumption that charcoal never reaches an equilibrium with the atmospheric radon

  13. Radon concentration calculation • Radon concentration is calculated by: • Rn = {net CPM} / { T(s) (E) (CF) (DF)} Where CPM – counts per minute T(s) – exposure time E – efficiency of detector CF – calibration factor DF – decay factor This method is effective for measuring concentrations above 4pCi/L as directed by EPA • Charcoal canister is ineffective for radon below 10Bq/m³

  14. Efficiency of Radon Detection recommended by the EPA

  15. Control Strategies

  16. Source removal • Selection of construction sites having low radium content • Knowledge of local soil characteristics such as permeability and moisture content • Removal and replacement of soil from a perimeter of 3m from the building foundation • The cost for this process is site specific and can range from $5,000 to $20,000

  17. New construction considerations • Radon concentration can be substantially reduced by new construction techniques • Provision of soil gas outlet to the sun slab and crawl spaces • Increasing the permeability by placing minimum of 4 inches of aggregate under slab • Double barrier approach can be used for slab-on-grade and crawl space construction

  18. Source Control by sealing Entry paths • Floor drains and sumps connected to drainage systems • Openings around utility lines • Hollow concrete block walls • Junction between walls and floor and slab • Cracks in building materials • Exposed soil and rocks having radon • Unpaved crawl space

  19. Sealing agents available and their characteristics • Caulking agents • Paints • Membranes • Cement-type materials • The sealants used should be moisture resistant • Paints for walls.

  20. Sunslab ventilation • The design of sunslab ventilation is house specific and depends on nature of foundation • Fan with a capability to create 50 – 100 Pa is installed on end of the pipe running from the basement • This can be made effective by placing multiple collection ports for each wall • This is good for old structures, but excessive cracks diminish its effectiveness • This is very effective if drain tiles surround the entire house

  21. Basement pressurization and Air cleaning • This method is highly effective method if the basement is airtight • Over pressurization of the basement drastically reduces the radon concentration below 4 pCi / L • This method is disadvantageous where there is increased ventilation and excessive windows and doors activity • This is one of the ways of reducing the radon concentration • During this process the air exchange rates are increased using the HVAC systems • Increased ventilation and activated carbon beds can remove the radon gas and its daughter products

  22. Electronic air cleaners and Increased ventilation • These cleaners have the capacity of reducing the radon gas and the potential alpha energy concentration (PAEC) by a factor of 2 – 20 • After various studies combination of ion generator with ceiling fan produced best results (87% reduction) • Another way of decreasing the radon from indoors is plate-out i.e. by pushing the charged progenies to walls or floors and then outdoors • Simple, but rather effective technique is to increase the ventilation rate • For homes with large crawl spaces mechanical ventilation is adopted to decreasge the radon entry into the building (four fold decrease)

  23. Adsorption • The radon adsorption can be another way in reducing its concentration and depends on following factors: • Air flow rates • Radon concentration • Relative humidity • Activated carbon is used as adsorbent (having high capacity for radon and minimum interference with moisture and other VOC’s)

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