Why Houses Have Radon

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Why Houses Have Radon




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Presentations text content in Why Houses Have Radon

Slide1

Why Houses Have Radon

Problems

Bruce Snead

MURC and NRPS at KSU

May 23, 2012

Slide2

Because they suck……The Predominant Driving Force is Building Induced Soil Suction

Buildings can create vacuums that will draw in soil gas

These vacuums may be very small and are referred to as air pressure differentials

Slide3

Radon Entry

Uranium

Radium

Radon

Slide4

Radon Entry Varies

from Building to Building

Sandy Soil

Strong

Source

Clay

All Homes Should be Tested!

Slide5

The Concentration of Radon in a Building Depends Upon:

1. Source of radon and its strength

2. Transport of radon

A. Pathways and B. Driving Forces (1) air pressure differences (2) diffusion (3) emanation (4) well water -- Environmental Effects 3. Ventilation rate of building

Slide6

How Long Does it Take for Radon to Accumulate in a Home? Dynamic Equilibrium

Once the radon entry rate into a building has been altered, time is needed for radon and RDP levels to stabilize

12 hours

is normally sufficient for dynamic equilibrium to occur in a home

12 Hours

House Closed

House

Open

Time

Rn

WL

Measurable Radioactivity

Slide7

Radon Concentrations Fluctuate

Slide8

Environmental Effects

Seasonal changes

Meteorological (weather) changes

Barometric Pressure RainWind

Slide9

Factors Affecting Indoor Radon

SourceUranium concentration in underlying geologic unit and emanated fraction of radonDetermined from Radium by measurements of core samples & flyover Radon (Bi-214) gamma raysTransport PathwaysSoil porosity and permeability, allowing radon to move under diffusion and pressure drive air flowDetermined from field soil & laboratory soil studiesOpening into the house, allowing diffusion and pressure drive air flowDetermined on a case by case analysisDriving Force (especially house depressurization)Factors causing house and basement depressurization bring radon indoors through the openings

Slide10

Radon Concentration in Soil Gas Vary from Location to Location

Simple soil gas source and ingress models fail to accurately predict indoor concentrations

Within short distances, depending on:Radium concentrationAirflow through soilSoil gas concentrations also change over time.

89,100 pCi/L

12,664 pCi/L

668 pCi/L

111 pCi/L

112 pCi/L

351 pCi/L

77,194 pCi/L

Lawrence Berkeley Laboratory

Slide11

Other Subsurface Contaminants that Pose Indoor Health Risks

An understanding of radon movement in soil is a useful beginning point to understand other subsurface contaminants

Methane and vinyl chlorides from landfills and other sources

Benzene, toluene and xylene from gasoline contamination

Tetrachloroethylene from dry cleaning

Slide12

Radon Surveys and Mapping of Potential Areas of Concern

Generally, high radon areas can be associated with radon rich soils, i.e., source strength

However, some areas not expected to have significant problems due to geology have indicated high potential, thus implicating the interaction of other factors

Sweden was the first country to make use of airborne gamma spectrometry data to make radon potential maps

(

Slide13

Granites

ShalesPhosphatesBased largely upon uranium exploration experiencesAerial radiometric data from gamma emissions from Bi-214

Geology Based Uranium Mapping: Pre-1986

Slide14

U.S. Radon Zone Map: 1993

Map based on

Geologic factors

Aerial surveys ~ uranium prospectingResults of home surveysPrimarily short-term tests in lowest livable level Home foundation typeSoil surveys Expected average short term Radon (pCi/L):Red = Zone 1 > 4.0High probabilityOrange = Zone 2 > 2 < 4.0Yellow = Zone 3 < 2.0Low probability

Should use map with EPA manual explaining methodology. Areas of high and low radon may be found in any zone.

Slide15

Iowa Radon Screening Tests

Slide16

Indoor Radon in a Community

Source: Mike Mudrey, 2005, UW-Madison

Test Results

< 4 pCi/L

4 - 10 10 - 12 12 - 16 16 – 20 20 – 30>30

Slide17

Radon Transport

Two components:

A. Pathways

Soil - high soil porosity or utility trenches, etc.

Building Shell - joints, cracks, earthen areas, utility penetrations, etc.

in the foundation

B. Driving Forces

Forces that pull or push radon toward the building and indoors.

Slide18

Pathways in Soil and Geology

Soil permeability

Greatest when soil is driest

Greatest in foundation backfill region compared to subslab zone

However, no measurable change in indoor entry rate ~ soil moisture or soil permeability

Conclusion: major entry rate factor is advection

Karst geology

Extraordinary soil and indoor fluctuations

Slide19

Pathways Through Foundations

Slide20

Foundation Type: Basement

(e.g., Poured, Masonry [Concrete Block] Walls)

Radon enters through

Cracks and penetrations in poured floors/walls

Concrete block sides and top row

Excavation makes soil more permeable

Slide21

Floor-to-Wall Joints are Important Entry Points

Soil around footing is disturbed by construction and permeable

Extends completely around perimeter.Interior finishing does not stop radon

Cold Joint

Channel Drain

Expansion Joint

Slide22

Radon Entry Through Water Drainage Systems

Radon can pass through porous drainage beds or “French Drains” into the home

Draintile (aka weeping tile) is frequently routed to interior sumps

Soil Gas

Upper Floor of Home

Sump Pit

Sump Pump

Perforated Foundation Drain

Sump Discharge

Soil Gas

CVC

©

Slide23

Foundation Type: Slab-on-Grade

Many openings:

Cracks,

Penetrations,Joints,Cold, ExpansionHollow blocks

Aggregate/Sand

Undisturbed Soil

Footing

Poured

Concrete

Wall

Plumbing

Penetration

Concrete

Block

Wall

Slab

Slide24

Slab Penetrations

Plumbing block-outs for tubs, commodes, showers, etc

Most slab penetrations are hidden during construction

Radon follows loose fill in plumbing trench and is drawn in through slab openings

Slide25

With fiberglass showersThe plumbing block-out typically remainsRadon can follow the plumbing trench and enter through block outIf this opening remains, it can limited the effectiveness of active soil depressurizationWith ceramic tile showersThe block-out is filled with concrete

Plumbing Block-Outs

Slide26

Foundation Type: Crawl Space

Large soil surface where suction from house is applied

Crawl vents are little help, especially in winter

Floor insulation is not a radon barrier

Slide27

Driving Forces

1) Air pressure differences

2) Diffusion

3) Emanation

4) Well water

Slide28

The Predominant Driving Force is Building Induced Soil Suction

Buildings can create vacuums that will draw in soil gas

These vacuums may be very small and are referred to as air pressure differentials

Slide29

Indoor to Outdoor Negative Pressures Causes Most Radon Entry

There are two causes of radon entry into a closed house due to pressure differences:

Environmental factors

indoor to outdoor temperature differencerain windfalling barometric pressureBuilding operating conditionshuman factorsmechanically induced

Slide30

www.eren.doe.gov/buildings/weatherization_assistance/stckeff.html

Neutral pressure plane refers the elevation in a home where there is no pressure difference between the indoors and outdoors

The elevation of the neutral plane is influenced by:The air tightness of the home The lower the indoor/outdoor exchange rate, the higher the neutral pressure planeThe operation of exhaust devices in the homeWind

The Concept of Neutral Pressure Plane and Air Exchange Rate

Slide31

Indoor to Soil Air Pressure

Slide32

Units of Measurement of Air Pressure or Vacuum

Air pressure (aka vacuum or differential pressure) are measured in terms of

Inches of water column or

Pascals (Pa) 248 Pa = 1 inch W.C.0.004 inch W.C. = about 1 Pa1 inch of water column is the difference in pressure needed to raise a column of water 1 inch (in the example to the right, 1 + 1 inch = 2 inches)

IN. W.C.

2

1

0

1

2

2

1

0

1

2

IN. W.C.

Slide33

Air Pressure Differentials Affect Soil Gas Entry Rates

If radon is present in soil, air pressure differentials will cause radon to enter building

Pressure differences and radon entry vary with time

(Pa)

0

540 (20)

1080

(40)

1620 (60)

2160 (80)

1

2

3

4

Days

Vacuum (Pa)

0

20

40

60

80

Bq/m

3

(pCi/L)

Radon

Slide34

Forced Air HVAC Systems Create Pressure Differences

Heating, Ventilation, and Air Conditioning (HVAC)

Indoor to outdoor and indoor zone to zone pressure differences

Use of exhaust fans

In forced air HVAC systems

Operation of blower increases upper floor radon

Unbalanced air flows

Leaky ductwork

Leaky return ducts in basements have been observed to depressurize the basement by 3 to 10 Pa

Sub slab ductwork

Slide35

Effect of Unbalanced HVAC System and Leaky Ductwork

Leaks in return create vacuums in specific levels of home

Levels of home with no supply vents can have high vacuums

Slide36

Return Ducts Beneath Slab – or How to Mine Radon!

Fresh

Air

HVAC

Fan

HVAC fan draws radon into leaky ducts

Highest entry when fan is on

Supply ducts can also be below slab

Sub-slab ducts are more common in big buildings

Slide37

Home Exhaust Systems:

Estimated Air Flows

Air-Tight Wood Stove Bathroom FansCentral Vacuum Clothes Dryer Combustion AppliancesConventional Range HoodDowndraft Range Exhaust Forced Air BlowerOpen Wood StoveWood Fireplace

~ 65 ~ 30 ~ 110~ 100~ 21 - 72~ 100 - 300up to 400Variable~ 24 - 90~ 170

Typical CFM

Slide38

Unplanned Thermal By-Passes Enhance Stack Effect

Slide39

Transport Mechanism: Soil Gas Entry Due to Air Pressure Differences

Building vacuums or soil pressures cause air from soil to enter through foundation openings

Soil gas enters all buildings and radon in the soil enters with it

This is the primary: entry mechanismfocus of mitigation

Slide40

Effects of Building Ventilation

Ventilation is the interaction of

A. Dilution

B. Changes in air pressure relationships

Slide41

Factors Generally Influencing Residential Ventilation Rates

Temperature and weather conditions

Occupant use of exhaust devices

Dwelling characteristics

(Sherman and Dickerhorf, 1998)

Leakage in ducts outside conditioned space when air handlers operate

Multistory dwellings are typically leakier than single story dwellings

Dwellings built before 1980 are leakier than newer dwellings

Retrofitted or weatherized dwellings are tighter than those without retrofitting or weatherization

Slide42

Residential Ventilation Rates and Indoor Radon Concentrations

Generally, indoor pollutant concentrations show an inverse relationship to ventilation. However, with radon . . .

Not found in Chicago-area house over a 5 months period Little correlation found in 101 houses

17 energy-efficient in 8 states and Canada,

55 conventional houses in Maryland,

29 houses in San Francisco area

Concluded radon source strength responsible for differences

No correlation found in 58 homes in

Charleston, Colorado Springs, Fargo and Portland, ME

Slide43

Residential Ventilation Rates and Indoor Radon Concentrations

Ventilation of houses is driven by 3 factors

Winter stack effect

General, most important in terms of indoor radon concentrations especially in houses with basements

Mechanical exhaust ventilation

General, second most important in terms of indoor radon concentrations

Wind effect

General, third most important in terms of indoor radon concentrations

However, this pattern has considerable variation across groups of houses

Source: Sherman, 1992

Slide44

Summary: Effect of Ventilation Rates on Indoor Radon Concentrations

Studies on groups of homes and individual homes

do NOT show a strong correlation between low ventilation rates and high radon

The radon source strength is the controlling variable

Low ventilation rates do not cause high radon, but rather the final concentration after entering the building

Two buildings with the same radon concentrations, but different ventilation rates, have different radon entry rates

In part, the indoor radon concentrations depend upon the portion of air infiltrating indoors that is soil gas versus outdoor air

As a proportion of total infiltration, soil gas ranges from 1 to 20%

Source:

Slide45

2) Radon Can Move by Diffusion Through Soils to the Indoors

Radon moves by diffusion from its higher concentration at its source to areas of lower concentration

Radon entry indoors from diffusion is about 1/30 of pressure -driven soil gas flow

Slide46

3) Transport Mechanism: Emanation of Radon from Surface of Materials

Radon entry from building materials is uncommon and generally insignificant

Sources includeRadium rich aggregate in concrete and plasterboardIf radon created on surface emits into room airRate depends on radium content and surface areaTypically dissipated by normal ventilationThere are exceptions

Ra

Rn

Rn

Ra

Slide47

Where Emanation from Materials Have Been an Issue

In Sweden, light weight concrete with alum shale aggregate was used in housing built between 1926 and 1975

In the southeast region of the U.S., some concrete mid- and high-rise condominiums have been found to have emanation issues

Florida, Georgia, North Carolina, Tennessee

To have an emanation issue, several variables are needed:

A material with uranium decay products (radium)

The greater the surface area, the greater likelihood of a problem

An enclosed space, such as a dwelling

The smaller the volume, the greater likelihood of a problem

The lower the indoor-outdoor ventilation rate, the greater likelihood of a problem

Slide48

4) Well Water Transport

High radon concentrations found in the late 1950s in Maine

The long-term amount of indoor airborne radon depends on several factors:

Radon concentration in the water

Amount of water used

Efficiency of transfer from water to the air

Volume of the house

Air-exchange rate of the house

Slide49

Transport Mechanism: Outgassing from Well Water

High entry isolated to some wells

May be significantSmall volume houses with high water useMore released from hot and aerated water use10,000: 1 ratio*Overall, about Bq/m3 10,000 (or pCi/L) of water, through normal water usage, adds about 1 additional Bq/m3 (or pCi/L) to house indoor airBased upon limited samplingHigher in water use areas, e.g., showers

Rn

Rn

Ra

Rn

w

Slide50

Summary: Contributions from Radon Driving Forces in Houses

The movement of soil gas into a home is the predominant entry route

These are averages and a particular home can be different, e.g.,

As soil gas entry is reduced, emanation and diffusion can become more important

Water

< 1%

Air Pressure

Differences

95 - 99%

Diffusion

1 - 4%

Emanation

< 1%

Radium Containing Soil

Radium Containing Soil

Slide51

Radon Entry Dynamics Summary

Can be influenced by the complex interaction of:

Building characteristics

Heating system (e.g., type, use)Pressure differencesHouse ~ soilIntra-zonal Dynamic ventilation rateWater source (e.g., radon concentration in well water)Building materials (emanation)Diffusive vs. convective flowOccupant activitiesWindow opening (e.g., location)Fireplace and wood stove useExhaust fan use

Local geology

(including karst) Soil Radium contentMoisture contentTemperature differencesPermeability Water table (e.g., fluctuation) Metrological factorsBarometric pressure changes Wind speed and directionPrecipitation (e.g., rate, amount)Season (e.g., indoor – outdoor temperature difference ~ stack effect)Snow cover or soil saturation

It is complex and varies from house to house

and varies over time but we:

Attempt to standardize for measurement

Attempt to diagnose for mitigation

Slide52

Program web site:

www.sosradon.org

www.radoncoursesonline.org

www.kansasradonprogram.org

Contact us at Kansas State University

radon@ksu.edu

Bruce Snead

785-532-4992

bsnead@ksu.edu

Slide53

Slide54


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