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Measuring Radon in Residential Properties How does radon enter a home?
Connecticut Radon Training Program 2006 31
Lesson 3
How does radon enter a home?
Slide 31
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
Slide 32
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
Measuring Radon in Residential Properties How does radon enter a home?
Connecticut Radon Training Program 2006 32
Slide 33
Requirements for radon to enter a home
1. A source of radon 2. A mechanism to transport radon from the source into the home
3. An opening or pathway into the home
Slide 34
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 35
Where radon comes from
Uranium238
Thorium234
Thorium230
Radium226
Radon222
Protactinium234
See handout 31
Measuring Radon in Residential Properties How does radon enter a home?
Connecticut Radon Training Program 2006 33
Slide 36
Sources of radon
• Soil and rock: most common source • Groundwater • Building materials containing uranium and radium
Slide 37
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
Slide 38
Overview Radon from soil and rock
– Drains – Sump holes – Dirt floors – Construction joints – Spaces around service pipes
• Radon enters soil gas • Soil gas moves from ground into air in home
• Usually enters through foundation – Cracks in walls and floors
Measuring Radon in Residential Properties How does radon enter a home?
Connecticut Radon Training Program 2006 34
Slide 39
Radon source 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 310
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
Slide 311
Radon in other water
• 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
Usually not a problem where homes
Measuring Radon in Residential Properties How does radon enter a home?
Connecticut Radon Training Program 2006 35
Slide 312
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
Slide 313
Strength of radon sources
Soil: moderate to weak radon source
Rock: strong radon source
Rock: 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 314
Questions?
• About radon sources
• Next –Mechanisms that transport radon into a home
Measuring Radon in Residential Properties How does radon enter a home?
Connecticut Radon Training Program 2006 36
Slide 315
Radon transport mechanisms
Average contribution to radon in a home
Diffusion (14%)
Emanation (25%)
Outgassing (less than 1%)
A ir pressure differences (8590%)
Push or pull radon into a home
• Air pressure differences
• Diffusion
• Emanation
• Outgassing
Slide 316
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
Slide 317
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
á Warm air á
Negative pressure
á Soil gas á (including radon)
á á
Measuring Radon in Residential Properties How does radon enter a home?
Connecticut Radon Training Program 2006 37
Slide 318
Air pressure differences Mechanical systems
• Heating, ventilation, and air conditioning (HVAC) systems – Air distribution blowers
– Furnaces – Boilers – Woodburning 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 319
Air pressure differences Environmental effects
•Weather –Seasons –Rain, snow, and frost –Wind
• Other factors that seal the soil around a home
Slide 320
Environmental effects Seasons
Warm weather • Open windows • Equal pressure indoors and outdoors – Less 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
Measuring Radon in Residential Properties How does radon enter a home?
Connecticut Radon Training Program 2006 38
Slide 321
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 shortterm tests, should windows be
open or closed?
Slide 322
Complex effects of good ventilation (open windows)
When you measure radon in shortterm 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 323
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
Measuring Radon in Residential Properties How does radon enter a home?
Connecticut Radon Training Program 2006 39
Slide 324
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 effects Wind
Slide 325
Environmental effects Factors that seal the soil
• Asphalt or concrete driveways
• Concrete patios
Prevent radon from escaping into outdoor air
Slide 326
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
Measuring Radon in Residential Properties How does radon enter a home?
Connecticut Radon Training Program 2006 310
Slide 327
Other radon transport mechanisms
• 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
á concentration á
Lower radon concentration
á á
Diffusion = movement through materials
Slide 328
Radon
• Some rocks and other building materials contain uranium or radium
Radon ↑
Radium ↑
Uranium
Emanation = emission of gas from a surface by radioactive decay
• 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
Other radon transport mechanisms
Slide 329
Outgassing = release of radon gas from water
Other radon transport mechanisms
Measuring Radon in Residential Properties How does radon enter a home?
Connecticut Radon Training Program 2006 311
Slide 330
Questions?
• About mechanisms that transport radon into a home
• Next –Pathways that allow radon to enter a home
Slide 331
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
Slide 332
Pathway characteristics
• Ease with which air moves through the pathway
• Distance from radium (radon source) • Connections with other pathways
Measuring Radon in Residential Properties How does radon enter a home?
Connecticut Radon Training Program 2006 312
Slide 333
Review Requirements for radon entry
1. Radon source 2. Mechanism to transport radon from source into home
3. Pathways into the home
These factors determine the amount of radon that enters a home.
Slide 334
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
Slide 335
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)
Because radon levels vary, testing must be done over a period of time
Factors – Air pressure changes – Wind speed and direction
– Indoor and outdoor temperature changes
– Rain, snow, and frost – Use of mechanical exhaust systems
Measuring Radon in Residential Properties How does radon enter a home?
Connecticut Radon Training Program 2006 313
Slide 336
Why this information matters
• Air pressure differences • Ventilation • Environmental effects
Procedures for measuring radon are designed to control for these factors
Slide 337
Summary
• Every home should be tested for radon
• Requirements for radon to enter a home –Radon source –Mechanism to transport radon –Pathway
See handout 33
Slide 338
Summary
• Sources – 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
Measuring Radon in Residential Properties How does radon enter a home?
Connecticut Radon Training Program 2006 314
Slide 339
Summary How radon enters a home
Slide 340
Activity
• 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
For a hypothetical client, summarize how radon enters a home
Slide 341
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 32 for a sample explanation
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