radon overview how radon enters the home. learning outcomes upon completion of this module you will...
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Radon OverviewHow Radon Enters the Home
Learning Outcomes
Upon completion of this module you will be able to:
Recall the predominant source of radon in the home
Identify the three requirements for radon to enter a home
Recognize what household activities release radon in water into the air
Learning Outcomes
Determine why one home has high radon levels but the next door neighbor does not
Identify the main radon transport mechan-ism into a home
Examine why radon levels in a home are higher in the winter than in the summer
Upon completion of this module you will be able to:
Radon in the Home
For most Americans, the greatest exposure to radon is in the 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 Every type of home
▪ Old or new▪ Drafty or well sealed▪ With or without a
basement
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
Requirements for Radon to Enter a Home
1. A source of radon2. A mechanism to transport radon from
the source into the home3. An opening or pathway into the home
Sources of Radon
Soil and rock: most common source Groundwater Building materials containing uranium
and radium
Overview: Radon From Soil and Rock
Radon enters soil gas. Soil gas moves from the ground into air in the home, usually through the foundation in:
Drains Cracks in walls and floors Sump holes Dirt floors Construction joints Spaces around service
pipes
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
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
Radon Source: Emanation
Building materials sometimes contain radium or uranium Brick Granite Concrete products Sheetrock Materials contaminated with radioactive refuse
(rarely used) Usually contribute little to indoor radon
Strengths of Radon Sources
Even homes next to each other may have different radon sources with different strengths.
Rock: strong source
Groundwater: weak source
Soil: moderate source
Radon Transport Mechanisms
Push or pull radon into a home Air pressure differences Diffusion Emanation Outgassing
Average contribution to radon in a home
Diffusion(1-4%)
Emanation (2-5%)
Outgassing (less than
1%)
Air pressure differences (85-90% )
Main Radon Transport Mechanism: Air Pressure Differences
Home creates a 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
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
Positive pressure
Warm air
Negative pressure
Soil gas (including radon)
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
Another Transport Mechanism: Diffusion
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 radonconcentration
Higher radon concentration
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
Summary
In this module we discussed:
The predominant source of radon in the home
The three requirements for radon to enter a home
What household activities release radon in water into the air
Summary
Why one home has high radon levels but the next door neighbor does not
The main radon transport mechanism into a home
Why radon levels in a home are higher in the winter than in the summer
In this module we discussed: