lesson 3
DESCRIPTION
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. - PowerPoint PPT PresentationTRANSCRIPT
Slide 4-2
Predicted average indoor radon levels (U.S.)
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.
Zone 1 (red): greater than
4 pCi/L Zone 2 (orange):
2-4 pCi/LZone 3 (yellow):
less than 2 pCi/L
Slide 4-3
Predicted average indoor radon levels (Connecticut)
Zone 1 (red): greater than
4 pCi/L Zone 2 (orange):
2-4 pCi/LZone 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.
Slide 4-4
Requirements for radon to enter a home
1. A source of radon2. A mechanism to transport
radon from the source into the home
3. An opening or pathway into the home
Slide 4-5
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
Slide 4-6
Uranium decay series
Uranium-238
Thorium-234
Thorium-230
Radium-226
Radon-222
Protactinium-234
Slide 4-7
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
Slide 4-8
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
Slide 4-9
Radon in groundwater
• 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
Usually a problem only in small, closed water systems
Slide 4-10
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
Slide 4-11
Radon in other water
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
Slide 4-12
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
Slide 4-13
Strength of radon sources
Soil: moderate to weak radon source
Rock: strong radon
sourceRock: strong radon source
Rock:moderate
radon source
Even homes next to each other may have different radon sources, with different strengths.
Groundwater containing radon
Slide 4-14
Radon transport mechanisms
Average contribution to radon in a home
Diffusion(1-4%)
Emanation (2-5%)
Outgassing (less than
1%)
Air pressure differences (85-90% )
Push or pull radon into a home
Slide 4-15
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
Slide 4-16
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
Slide 4-17
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
Slide 4-18
Air pressure differences Environmental effects
• Weather– Seasons– Rain, snow,
and frost– Wind
• Other factors that seal the soil around a home
Slide 4-19
Environmental effectsSeasons
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
Usually more radon enters in winter
Slide 4-20
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?
Slide 4-21
Complex effects of good ventilation (open windows)
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
Slide 4-22
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
Slide 4-23
Wind
Lower pressure
down-wind
Higher pressure upwind
Don’t measure radon during high winds because results may not show typical levels.
Downwind draft effect • Changes pressure around the home• Higher pressure in soil as wind pushes
beneath soil
Environmental effectsWind
Slide 4-24
Environmental effectsFactors that seal the soil
Prevent radon escape into outdoor air
• Asphalt or concrete driveways
• Concrete patios
Slide 4-25
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 Higher radon
concentration
Lower radonconcentration
Slide 4-26
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
Slide 4-28
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
Slide 4-29
Pathway characteristics
• Ease with which air moves through the pathway
• Distance from radium (radon source)• Connections with other pathways
Slide 4-30
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)
Slide 4-31
Radon levels vary
• 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
Because radon levels vary, testing must be done over a period of time
Slide 4-33
Summary
• Every home should be tested for radon
• Requirements for radon to enter a home:– Radon source– Mechanism to transport radon– Pathway
Slide 4-34
Summary
• 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
Slide 4-35
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