0. Measuring Radon in Residential Properties How does radon enter a home?
Lesson 3
How does radon enter a home?
Note that people may also be exposed to radon in schools, offices, other buildings, and mines, but this course focuses on measuring radon in homes.
Connecticut Radon Measurement
Training Program

1. Radon in the home
For most Americans, greatest exposure to radon is in home, especially in rooms that are
Below grade (such as basements)
In contact with the ground
Immediately above the first two categories
High radon levels have been found in
Homes throughout the United States
Homes throughout Connecticut
Every type of home
Old or new
Drafty or well sealed
With or without a basement

2. Importance of testing
Even neighboring homes may have very different radon levels
EPA recommends that all homes be tested for radon
Testing is the only accurate way to determine the radon level in any home

3. 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

4. Level of radon in a home Depends on
Strength of radon sources: most important factor
Distance of the sources from the home
Ease of transport into the home
Ventilation in the home
Environmental factors

5. Measuring Radon in Residential Properties
How does radon enter a home?
Where radon comes from
Uranium-238
Thorium-234
Protactinium-234
Thorium-230
Do not spend a lot of time on this slide. It merely illustrates where radon comes from.
Radium-226
Radon-222
See handout 3-1
Connecticut Radon Measurement
Training Program

6. Sources of radon Soil and rock: most common source Groundwater
Building materials containing uranium and radium

7. Radon source Soil and rock
Measuring Radon in Residential Properties
How does radon enter a home?
Radon source Soil and rock
Uranium is present at about 0.5 to 5 parts per million (ppm) in common rocks and soil
Uranium and radium especially common in granites, shales, and limestones
Under a home, they can be source of radon
Uranium decays into radium
Radium decays into radon
Image:
Connecticut Radon Measurement
Training Program

8. Overview Radon from soil and rock
Measuring Radon in Residential Properties
How does radon enter a home?
Overview Radon from soil and rock
Radon enters soil gas
Soil gas moves from ground into air in home
Usually enters through foundation
Cracks in walls and floors
Drains
Sump holes
Dirt floors
Construction joints
Spaces around service pipes
Image: GSF – National Research Center for Environmental Health, Neuherberg, Germany,
Connecticut Radon Measurement
Training Program

9. Radon source 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 from groundwater sources
Measuring Radon in Residential Properties
How does radon enter a home?
Radon from groundwater sources
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
Shower image:
Dishwashing image:
Connecticut Radon Measurement
Training Program

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

12. Radon source 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. Questions? About radon sources Next
Mechanisms that transport radon into a home

15. Radon transport mechanisms
Push or pull radon into a home
Air pressure differences
Diffusion
Emanation
Outgassing

16. Main radon transport mechanism Air pressure differences
Measuring Radon in Residential Properties
How does radon enter a home?
Main radon transport mechanism Air 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
Graphic: U.S. Environmental Protection Agency, 2004, Consumer’s Guide to Radon Reduction: How to Fix Your Home.
Connecticut Radon Measurement
Training Program

17. Air pressure differences Stack effect
Heated indoor air rises and escapes through cracks and holes at top of home
Creates positive air pressure at top of home
Creates negative air pressure (vacuum) at bottom
Vacuum draws in soil gas, including radon
Effect is greatest during coldest months
Thermal bypasses increase effect
Positive pressure
 Warm air 
Negative pressure  
 Soil gas 
(including radon)

18. Air pressure differences Mechanical systems
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

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

20. Environmental effects Seasons
Usually more radon enters in winter
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

21. Complex effects of good ventilation (open windows)
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?

22. Complex effects of good ventilation (open windows)
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, windows must be kept closed

23. 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

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

25. Environmental effects Factors that seal the soil
Prevent radon from escaping into outdoor air
Asphalt or concrete driveways
Concrete patios

26. Summary Air pressure Main mechanism that brings radon into a home
Difference in air pressure between indoor and outdoor air
Main causes of air pressure differences
Temperature differences between indoor and outdoor air
Mechanical systems
Environmental factors

27. Other radon transport mechanisms
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 

28. Other radon transport mechanisms
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
Radon ↑
Radium
Uranium
Radon

29. Other radon transport mechanisms
Outgassing = release of radon gas from water

30. Questions? About mechanisms that transport radon into a home Next
Pathways that allow radon to enter a home

31. Radon pathways into the home
Natural pathways
Pores or empty spaces in soil
Cracks in underlying rocks
Earthen areas in basements
Artificial pathways
Openings for utility lines and plumbing
Water drainage systems
Other openings in foundations

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

33. Review Requirements for radon entry
Radon source
Mechanism to transport radon from source into home
Pathways into the home
These factors determine the amount of radon that enters a home.

34. Radon levels vary In space
From geographic area to geographic area
From home to home
From level to level within a home
Usually highest in lower levels of home
Higher readings in upper levels suggest unusual radon entry factors

35. Radon levels vary Over time
In time
From season to season
From day to day
From hour to hour
With changes to the home (such as additions)
Factors
Air pressure changes
Wind speed and direction
Indoor and outdoor temperature changes
Rain, snow, and frost
Use of mechanical exhaust systems
Because radon levels vary, testing must be done over a period of time

36. Why this information matters
Procedures for measuring radon are designed to control for these factors
Air pressure differences
Ventilation
Environmental effects

37. Summary Every home should be tested for radon
Requirements for radon to enter a home
Radon source
Mechanism to transport radon
Pathway
See handout 3-3

38. Summary Sources Mechanisms Pathways Variation in radon levels
Soil and rock
Groundwater
Building materials
Mechanisms
Air pressure differences
Diffusion
Emanation
Outgassing
Pathways
Distance from radon source
Ease with which air moves
Connections with other pathways
Variation in radon levels
In space
In time
With changes in the home

39. Summary How radon enters a home
Measuring Radon in Residential Properties
How does radon enter a home?
Summary How radon enters a home
Source: Natural Resources Canada,
Connecticut Radon Measurement
Training Program

40. 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
Hypothetical client:
an attorney

41. Activity review Is the explanation complete? Is the explanation clear?
Does the explanation contain the right level of technical detail for this client?
See handout 3-2 for a sample explanation

42. Questions
About how radon enters a home

43. Check your understanding
See handout 3-4