Lesson 3

How does radon enter a home?

Slide 3-2

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 3-3

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

Slide 3-4

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 3-5

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 3-6

Where radon comes from

Uranium-238

Thorium-234

Thorium-230

Radium-226

Radon-222

Protactinium-234

See handout 3-1

Slide 3-7

Sources of radon

• Soil and rock: most common source• Groundwater• Building materials containing

uranium and radium

Slide 3-8

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 3-9

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

Slide 3-10

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 3-11

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 3-12

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

Slide 3-13

Radon sourceBuilding 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 3-14

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 3-15

Questions?

• About radon sources

• Next– Mechanisms that transport radon into a

home

Slide 3-16

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

• Air pressure differences

• Diffusion

• Emanation

• Outgassing

Slide 3-17

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 3-18

Air pressure differencesStack 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)

Slide 3-19

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 3-20

Air pressure differences Environmental effects

• Weather– Seasons– Rain, snow,

and frost– Wind

• Other factors that seal the soil around a home

Slide 3-21

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 3-22

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, should windows be

open or closed?

Slide 3-23

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 3-24

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 3-25

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 3-26

Environmental effectsFactors that seal the soil

• Asphalt or concrete driveways

• Concrete patios

Prevent radon from escaping into outdoor air

Slide 3-27

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

Slide 3-28

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 concentration

Lower radonconcentration

Diffusion = movement through materials

Slide 3-29

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 3-30

Outgassing = release of radon gas from water

Other radon transport mechanisms

Slide 3-31

Questions?

• About mechanisms that transport radon into a home

• Next– Pathways that allow radon to enter a

home

Slide 3-32

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 3-33

Pathway characteristics

• Ease with which air moves through the pathway

• Distance from radium (radon source)• Connections with other pathways

Slide 3-34

ReviewRequirements for radon entry

1. Radon source2. Mechanism to transport radon from

source into home3. Pathways into the home

These factors determine the amount of radon that enters a home.

Slide 3-35

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 3-36

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

Slide 3-37

Why this informationmatters

• Air pressure differences• Ventilation• Environmental effects

Procedures for measuring radon are designed to control for these factors

Slide 3-38

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

Slide 3-39

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

Slide 3-40

SummaryHow radon enters a home

Slide 3-41

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 3-42

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

Slide 3-43

Questions

• About how radon enters a home

Slide 3-44

Check your understanding

• See handout 3-4