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: