measuring radon in residential properties how … radon in residential properties how does radon ......

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



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



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



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



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



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



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



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



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



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


Slide 329

Outgassing = release of radon gas from water




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



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



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



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



Slide 342

Questions

• About how radon enters a home

Slide 343

Check your understanding

• See handout 34

measuring radon in residential properties how … radon in residential properties how does radon ......

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