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Lesson 3

Lesson 3. How does radon enter a home?. Predicted average indoor radon levels (U.S.). Zone 1 (red): greater than 4 pCi/L Zone 2 (orange): 2-4 pCi/L Zone 3 (yellow): less than 2 pCi/L.

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Lesson 3

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  1. Lesson 3 How does radon enter a home?

  2. Predicted average indoor radon levels (U.S.) Zone 1 (red): greater than 4 pCi/L Zone 2 (orange): 2-4 pCi/L Zone 3 (yellow): less than 2 pCi/L This map cannot be used to determine the radon level of a particular home. Homes with high levels of radon have been found in all three zones. All homes—regardless of their zone—should be tested.

  3. Predicted average indoor radon levels (Connecticut) Zone 1 (red): greater than 4 pCi/L Zone 2 (orange): 2-4 pCi/L Zone 3 (yellow): less than 2 pCi/L This map cannot be used to determine the radon level of a particular home. Homes with high levels of radon have been found in all three zones. All homes—regardless of their zone—should be tested.

  4. Requirements for radon to enter a home • A source of radon • A mechanism to transport radon from the source into the home • An opening or pathway into the home

  5. Level of radon in a home Depends on • Strength of radon sources: most important factor • Distanceof the sources from the home • Ease of transportinto the home • Ventilationin the home • Environmental factors

  6. Uranium decay series Uranium-238 Thorium-234 Protactinium-234 Thorium-230 Radium-226 Radon-222

  7. Sources of radon • Soil and rock • Uranium is present at about 0.5 to 5 parts per million (ppm) in common rocks and soil • Uranium decays into radium • Radium decays into radon • Groundwater • Building materials containing uranium and radium

  8. Radon from soil and rock • Soil gas, including radon, seeps from the ground into the air in the home • Usually enters through the foundation • Cracks in walls and floors • Drains • Sump holes • Dirt floors • Construction joints • Spaces around service pipes

  9. Radon in groundwater Usually a problem only in small, closed water systems • Where underlying rocks contain high levels of uranium • Where homes rely on groundwater from private wells or small public waterworks as the main water source

  10. Radon in small, closed groundwater systems • Radon does not have time to decay into harmless by-products before entering a home • Once inside the home, radon escapes from the water into the air during normal household activities: • Showering • Washing clothes or dishes • Flushing toilets

  11. Usually not a problem where homes Use surface water (lakes, streams, rivers, and reservoirs) Radon usually escapes into the air before it reaches a home Use groundwater from large public systems Water is aerated (mixed with air), which allows radon to escape Longer transit times allow most of remaining radon to decay into harmless products Radon in other water

  12. Radon in building materials • Materials sometimes contain radium or uranium • Brick • Granite • Concrete products • Sheet rock • Materials contaminated with radioactive refuse (rarely used) • Usually contribute little to indoor radon

  13. Strength of radon sources Even homes next to each other may have different radon sources, with different strengths. Soil: moderate to weak radon source Groundwater containing radon Rock: moderate radon source Rock: strong radon source Rock: strong radon source

  14. Radon transport mechanisms Push or pull radon into a home

  15. Radon transport mechanismsAir pressure differences • Home creates small vacuum (negative air pressure) • Draws in soil gas, including radon • Vacuum caused by • Temperature differences between outside and inside air (stack effect) • Mechanical systems • Environmental factors

  16. Air pressure differencesStack effect • Heated indoor air rises and moves out of cracks and holes at the top of the house • Creates positive air pressure at the top of the home • Creates negative air pressure (vacuum) at the bottom • Vacuum draws in soil gas, including radon • Effect is greatest during coldest months, when homes are closed up Positive pressure  Warm air  Negative pressure   Soil gas (including radon) • Effect increases because of thermal bypasses

  17. Heating, ventilation, and air conditioning (HVAC) systems Air distribution blowers Furnaces Boilers Wood-burning fireplaces Woodstoves Other combustion systems Home exhaust systems (vent air to outside) Clothes dryers Exhaust fans in bathrooms, kitchens, or attics Central vacuum cleaners Air pressure differencesMechanical systems

  18. Weather Seasons Rain, snow, and frost Wind Other factors that seal the soil around a home Air pressure differences Environmental effects

  19. Warm weather Open windows Equal pressure indoors and outdoors L ess radon enters Good ventilation dilutes radon concentration Cold weather Closed windows Lower pressure indoors More radon enters Poor ventilation traps radon inside Environmental effectsSeasons Usually more radon enters in winter

  20. Reduces vacuum effect Generally reduces radon entry Dilutes radon in home But may also increase stack effect Thereby increases radon entry When you measure radon in short-term tests, should windows be open or closed? Complex effects of good ventilation (open windows)

  21. When you measure radon in short-term tests, windows must be kept closed Reduces vacuum effect Generally reduces radon entry Dilutes radon in home But may also increase stack effect Thereby increases radon entry Complex effects of good ventilation (open windows)

  22. Environmental effects Rain, snow, and frost • Rain, snow, and frost can seal the soil • Prevent radon from escaping from around the foundation • Rain can force soil gas into the home

  23. Environmental effectsWind Downwind draft effect • Changes pressure around the home • Higher pressure in soil as wind pushes beneath soil Don’t measure radon during high winds because results may not show typical levels. Wind Higher pressure upwind Lower pressure down-wind

  24. Environmental effectsFactors that seal the soil Prevent radon escape into outdoor air • Asphalt or concrete driveways • Concrete patios

  25. Radon transport mechanismsDiffusion Diffusion = movement through materials • Radon concentration is higher at its source (underlying soil or foundation) than in indoor air • Radon moves from area of higher concentration to area of lower concentration Lower radon concentration  Higher radon concentration

  26. Radon transport mechanismsEmanation Emanation = emission of gas from a surface by radioactive decay • Some rocks and other building materials contain uranium or radium • As these elements decay, radon may be created on their surfaces • The radon may be emitted into a room • Emanation rate depends on • Amount of radioactive materials • Surface area of the materials Uranium  Radium  Radon

  27. Radon transport mechanismsOutgassing

  28. Radon transport Pathways into the home • Natural • Pores or empty spaces in soil • Cracks in underlying rocks • Earthen areas in basements • Artificial • Fill below foundations • Trenches for utility lines and plumbing • Water drainage systems • Other openings in foundations

  29. Pathway characteristics • Ease with which air moves through the pathway • Distance from radium (radon source) • Connections with other pathways

  30. Radon entry and levels vary • In space • From geographic area to geographic area • From home to home • From level to level within a home • In time • From season to season • From day to day • From hour to hour • With changes to the home (such as additions)

  31. Usually highest in lower levels of home Higher readings in upper levels suggest unusual radon entry factors Levels vary because air pressure factors vary Temperature Rain, snow, and frost Use of mechanical exhaust systems Radon levels vary Because radon levels vary, testing must be done over a period of time

  32. SummaryHow radon enters a home

  33. Summary • Every home should be tested for radon • Requirements for radon to enter a home: • Radon source • Mechanism to transport radon • Pathway

  34. Sources Soil and rock Groundwater Building materials Mechanisms Air pressure differences Diffusion Emanation Outgassing Pathways Natural Artificial Variation in radon levels In space In time With changes in the home Summary

  35. Activity For a hypothetical client, summarize how radon enters a home • Importance of testing every home • Factors that determine the radon level in a home • Most common sources of radon • Common mechanisms of radon entry • Pathways into the home • Variations in radon levels over space and time

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