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Radon - PowerPoint PPT Presentation


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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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introduction
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
sources of radon
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
factors affecting transport of radon to the surface
Factors affecting transport of Radon to the surface
  • Soil permeability
  • Porosity
  • Water content
  • Temperature
  • Pressure difference between soil and building structure
sources of radon1
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
sampling methods
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%
sampling methods1
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
integrated sampling
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
radon concentration calculation
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
source removal
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
new construction considerations
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
source control by sealing entry paths
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
sealing agents available and their characteristics
Sealing agents available and their characteristics
  • Caulking agents
  • Paints
  • Membranes
  • Cement-type materials
  • The sealants used should be moisture resistant
  • Paints for walls.
sunslab ventilation
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
basement pressurization and air cleaning
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
electronic air cleaners and increased ventilation
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)
adsorption
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)