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1 Why Houses Have Radon Problems Bruce Snead MURC and NRPS at KSU May 23, 2012.

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Presentation on theme: "1 Why Houses Have Radon Problems Bruce Snead MURC and NRPS at KSU May 23, 2012."— Presentation transcript:

1 1 Why Houses Have Radon Problems Bruce Snead MURC and NRPS at KSU May 23, 2012

2 2 Because they suck……The Predominant Driving Force is Building Induced Soil Suction n Buildings can create vacuums that will draw in soil gas n These vacuums may be very small and are referred to as air pressure differentials

3 3 Radon Entry Uranium Radium Radon

4 4 Radon Entry Varies from Building to Building Sandy Soil Strong Source Clay All Homes Should be Tested!

5 5 The Concentration of Radon in a Building Depends Upon: 1. Source of radon and its strength 2. Transport of radon A. Pathways and A. Pathways and B. Driving Forces B. Driving Forces (1) air pressure differences (1) air pressure differences (2) diffusion (2) diffusion (3) emanation (3) emanation (4) well water (4) well water -- Environmental Effects -- Environmental Effects 3. Ventilation rate of building

6 6 How Long Does it Take for Radon to Accumulate in a Home? Dynamic Equilibrium n Once the radon entry rate into a building has been altered, time is needed for radon and RDP levels to stabilize n 12 hours is normally sufficient for dynamic equilibrium to occur in a home 12 Hours House Closed HouseOpen Time Rn WL Measurable Radioactivity

7 7 Radon Concentrations Fluctuate

8 8 Environmental Effects n Seasonal changes n Meteorological (weather) changes l Barometric Pressure l Rain l Wind

9 9 F actors Affecting Indoor Radon  Source  Uranium concentration in underlying geologic unit and emanated fraction of radon  Determined from Radium by measurements of core samples & flyover Radon (Bi-214) gamma rays  Transport  Pathways  Soil porosity and permeability, allowing radon to move under diffusion and pressure drive air flow  Determined from field soil & laboratory soil studies  Opening into the house, allowing diffusion and pressure drive air flow  Determined on a case by case analysis n Driving Force (especially house depressurization) l Factors causing house and basement depressurization bring radon indoors through the openings

10 10 Radon Concentration in Soil Gas Vary from Location to Location n Simple soil gas source and ingress models fail to accurately predict indoor concentrations n Within short distances, depending on: l Radium concentration l Airflow through soil n Soil 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

11 11 Other Subsurface Contaminants that Pose Indoor Health Risks n An understanding of radon movement in soil is a useful beginning point to understand other subsurface contaminants l Methane and vinyl chlorides from landfills and other sources l Benzene, toluene and xylene from gasoline contamination l Tetrachloroethylene from dry cleaning

12 12 Radon Surveys and Mapping of Potential Areas of Concern n n Generally, high radon areas can be associated with radon rich soils, i.e., source strength n n However, some areas not expected to have significant problems due to geology have indicated high potential, thus implicating the interaction of other factors n n Sweden was the first country to make use of airborne gamma spectrometry data to make radon potential maps (

13 13 n Granites n Shales n Phosphates n Based largely upon uranium exploration experiences l Aerial radiometric data from gamma emissions from Bi-214 Geology Based Uranium Mapping: Pre-1986

14 14 U.S. Radon Zone Map: 1993 n Map based on n Geologic factors n Aerial surveys ~ uranium prospecting n Results of home surveys n Primarily short-term tests in lowest livable level n Home foundation type n Soil surveys n Expected average short term Radon (pCi/L): l Red = Zone 1 > 4.0 l High probability l Orange = Zone 2 > 2 < 4.0 l Yellow = Zone 3 < 2.0 l Low probability Should use map with EPA manual explaining methodology. Areas of high and low radon may be found in any zone.

15 15 Iowa Radon Screening Tests

16 16 Indoor Radon in a Community Source: Mike Mudrey, 2005, UW-Madison Test Results < 4 pCi/L – – 30 >30

17 17 Radon Transport Two components: A. Pathways l Soil - high soil porosity or utility trenches, etc. l Building Shell - joints, cracks, earthen areas, utility penetrations, etc. in the foundation in the foundation B. Driving Forces l Forces that pull or push radon toward the building and indoors.

18 18 Pathways in Soil and Geology n Soil permeability l Greatest when soil is driest l Greatest in foundation backfill region compared to subslab zone l However, no measurable change in indoor entry rate ~ soil moisture or soil permeability F Conclusion: major entry rate factor is advection n Karst geology l Extraordinary soil and indoor fluctuations

19 19 Pathways Through Foundations

20 20 Foundation Type: Basement (e.g., Poured, Masonry [Concrete Block] Walls) n Radon enters through l Cracks and penetrations in poured floors/walls l Concrete block sides and top row n Excavation makes soil more permeable

21 21 Floor-to-Wall Joints are Important Entry Points n Soil around footing is disturbed by construction and permeable n Extends completely around perimeter. n Interior finishing does not stop radon Cold Joint Channel Drain Expansion Joint

22 22 Radon Entry Through Water Drainage Systems n Radon can pass through porous drainage beds or “French Drains” into the home n 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 CVC ©

23 23 Foundation Type: Slab-on-Grade n Many openings: l Cracks, l Penetrations, l Joints, F Cold, F Expansion l Hollow blocks Aggregate/Sand Undisturbed Soil Footing PouredConcreteWall PlumbingPenetration Concrete Block Wall Slab

24 24 Slab Penetrations n Plumbing block-outs for tubs, commodes, showers, etc n Most slab penetrations are hidden during construction n Radon follows loose fill in plumbing trench and is drawn in through slab openings

25 25 n With fiberglass showers l The plumbing block-out typically remains l Radon can follow the plumbing trench and enter through block out l If this opening remains, it can limited the effectiveness of active soil depressurization n With ceramic tile showers l The block-out is filled with concrete Plumbing Block-Outs

26 26 Foundation Type: Crawl Space n Large soil surface where suction from house is applied n Crawl vents are little help, especially in winter n Floor insulation is not a radon barrier

27 27 Driving Forces 1) Air pressure differences 2) Diffusion 3) Emanation 4) Well water

28 28 The Predominant Driving Force is Building Induced Soil Suction n Buildings can create vacuums that will draw in soil gas n These vacuums may be very small and are referred to as air pressure differentials

29 29 Indoor to Outdoor Negative Pressures Causes Most Radon Entry There are two causes of radon entry into a closed house due to pressure differences: l Environmental factors l indoor to outdoor temperature difference l rain l wind l falling barometric pressure l Building operating conditions l human factors l mechanically induced

30 30  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 plane The operation of exhaust devices in the home Wind The Concept of Neutral Pressure Plane and Air Exchange Rate

31 31 Indoor to Soil Air Pressure

32 32 Units of Measurement of Air Pressure or Vacuum n Air pressure (aka vacuum or differential pressure) are measured in terms of n Inches of water column or n Pascals (Pa) l 248 Pa = 1 inch W.C. l inch W.C. = about 1 Pa n 1 inch of water column is the difference in pressure needed to raise a column of water 1 inch (in the example to the right, inch = 2 inches) IN. W.C

33 33 Air Pressure Differentials Affect Soil Gas Entry Rates n If radon is present in soil, air pressure differentials will cause radon to enter building n Pressure differences and radon entry vary with time (Pa) (20) 1080(40) 1620 (60) 2160 (80) 1234 Days Vacuum (Pa) Bq/m 3 (pCi/L) Radon

34 34 Forced Air HVAC Systems Create Pressure Differences n Heating, Ventilation, and Air Conditioning (HVAC) n Indoor to outdoor and indoor zone to zone pressure differences l Use of exhaust fans l In forced air HVAC systems F Operation of blower increases upper floor radon F Unbalanced air flows F Leaky ductwork Leaky return ducts in basements have been observed to depressurize the basement by 3 to 10 PaLeaky return ducts in basements have been observed to depressurize the basement by 3 to 10 Pa F Sub slab ductwork

35 35 Effect of Unbalanced HVAC System and Leaky Ductwork n Leaks in return create vacuums in specific levels of home n Levels of home with no supply vents can have high vacuums

36 36 Return Ducts Beneath Slab – or How to Mine Radon! Fresh Air HVAC Fan n HVAC fan draws radon into leaky ducts n Highest entry when fan is on n Supply ducts can also be below slab n Sub-slab ducts are more common in big buildings

37 37 Home Exhaust Systems: Estimated Air Flows Air-Tight Wood Stove Bathroom Fans Central Vacuum Clothes Dryer Combustion Appliances Conventional Range Hood Downdraft Range Exhaust Forced Air Blower Open Wood Stove Wood Fireplace ~ 65 ~ 30 ~ 110 ~ 100 ~ ~ up to 400 Variable ~ ~ 170 Typical CFM

38 38 Unplanned Thermal By-Passes Enhance Stack Effect

39 39 Transport Mechanism: Soil Gas Entry Due to Air Pressure Differences n Building vacuums or soil pressures cause air from soil to enter through foundation openings n Soil gas enters all buildings and radon in the soil enters with it n This is the primary: l entry mechanism l focus of mitigation

40 40 Effects of Building Ventilation Ventilation is the interaction of A. Dilution B. Changes in air pressure relationships

41 41 Factors Generally Influencing Residential Ventilation Rates n Temperature and weather conditions n Occupant use of exhaust devices n Dwelling characteristics (Sherman and Dickerhorf, 1998) l Leakage in ducts outside conditioned space when air handlers operate l Multistory dwellings are typically leakier than single story dwellings l Dwellings built before 1980 are leakier than newer dwellings l Retrofitted or weatherized dwellings are tighter than those without retrofitting or weatherization

42 42 Residential Ventilation Rates and Indoor Radon Concentrations n Generally, indoor pollutant concentrations show an inverse relationship to ventilation. However, with radon... l Not found in Chicago-area house over a 5 months period Little correlation found in 101 houses F 17 energy-efficient in 8 states and Canada, F 55 conventional houses in Maryland, F 29 houses in San Francisco area F Concluded radon source strength responsible for differences l No correlation found in 58 homes in F Charleston, Colorado Springs, Fargo and Portland, ME

43 43 Residential Ventilation Rates and Indoor Radon Concentrations Ventilation of houses is driven by 3 factors 1. 1.Winter stack effect General, most important in terms of indoor radon concentrations especially in houses with basements 2. 2.Mechanical exhaust ventilation General, second most important in terms of indoor radon concentrations 3. 3.Wind effect General, third most important in terms of indoor radon concentrations l However, this pattern has considerable variation across groups of houses Source: Sherman, 1992

44 44 Summary: Effect of Ventilation Rates on Indoor Radon Concentrations n Studies on groups of homes and individual homes do NOT show a strong correlation between low ventilation rates and high radon l The radon source strength is the controlling variable l Low ventilation rates do not cause high radon, but rather the final concentration after entering the building l Two buildings with the same radon concentrations, but different ventilation rates, have different radon entry rates F 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:As a proportion of total infiltration, soil gas ranges from 1 to 20% Source:

45 45 2) Radon Can Move by Diffusion Through Soils to the Indoors n Radon moves by diffusion from its higher concentration at its source to areas of lower concentration n Radon entry indoors from diffusion is about 1/30 of pressure - driven soil gas flow

46 46 3) Transport Mechanism: Emanation of Radon from Surface of Materials n Radon entry from building materials is uncommon and generally insignificant n Sources include n Radium rich aggregate in concrete and plasterboard n If radon created on surface emits into room air n Rate depends on radium content and surface area l Typically dissipated by normal ventilation  There are exceptions Ra Rn Rn Ra

47 47 Where Emanation from Materials Have Been an Issue n In Sweden, light weight concrete with alum shale aggregate was used in housing built between 1926 and 1975 n In the southeast region of the U.S., some concrete mid- and high- rise condominiums have been found to have emanation issues n Florida, Georgia, North Carolina, Tennessee n To have an emanation issue, several variables are needed: n A material with uranium decay products (radium) n The greater the surface area, the greater likelihood of a problem n An enclosed space, such as a dwelling n The smaller the volume, the greater likelihood of a problem n The lower the indoor-outdoor ventilation rate, the greater likelihood of a problem

48 48 4) Well Water Transport n High radon concentrations found in the late 1950s in Maine n The long-term amount of indoor airborne radon depends on several factors: l Radon concentration in the water l Amount of water used l Efficiency of transfer from water to the air l Volume of the house l Air-exchange rate of the house

49 49 Transport Mechanism: Outgassing from Well Water n High entry isolated to some wells l May be significant l Small volume houses with high water use l More released from hot and aerated water use n 10,000: 1 ratio* l Overall, about Bq/m 3 10,000 (or pCi/L) of water, through normal water usage, adds about 1 additional Bq/m 3 (or pCi/L)to house indoor air l Overall, about Bq/m 3 10,000 (or pCi/L) of water, through normal water usage, adds about 1 additional Bq/m 3 (or pCi/L) to house indoor air l Based upon limited sampling l Higher in water use areas, e.g., showers

50 50 Summary: Contributions from Radon Driving Forces in Houses n The movement of soil gas into a home is the predominant entry route n These are averages and a particular home can be different, e.g., n As soil gas entry is reduced, emanation and diffusion can become more important Water < 1% Air Pressure Differences % Diffusion 1 - 4% Emanation < 1% Radium Containing Soil

51 51 Radon Entry Dynamics Summary Can be influenced by the complex interaction of: n Building characteristics l Heating system (e.g., type, use) l Pressure differences F House ~ soil F Intra-zonal l Dynamic ventilation rate l Water source (e.g., radon concentration in well water) l Building materials (emanation) n Diffusive vs. convective flow n Occupant activities l Window opening (e.g., location) l Fireplace and wood stove use l Exhaust fan use n Local geology (including karst) n Soil l Radium content l Moisture content l Temperature differences l Permeability l Water table (e.g., fluctuation) n Metrological factors l Barometric pressure changes l Wind speed and direction l Precipitation (e.g., rate, amount) l Season (e.g., indoor – outdoor temperature difference ~ stack effect) l Snow cover or soil saturation It is complex and varies from house to house and varies over time but we: 1.Attempt to standardize for measurement 2.Attempt to diagnose for mitigation

52 52 Program web site: Contact us at Kansas State University Bruce Snead


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