Lesson 3 How does radon enter a home?

Slide 3-1 Predicted average indoor radon levels (U.S.) This map cannot be used to determine the radon level of a particular home. Homes with high levels of radon have been found in all three zones. All homes—regardless of their zone—should be tested. Zone 1 (red): greater than 4 pCi/L Zone 2 (orange): 2-4 pCi/L Zone 3 (yellow): less than 2 pCi/L

Slide 3-2 Predicted average indoor radon levels (Connecticut) Zone 1 (red): greater than 4 pCi/L Zone 2 (orange): 2-4 pCi/L Zone 3 (yellow): less than 2 pCi/L This map cannot be used to determine the radon level of a particular home. Homes with high levels of radon have been found in all three zones. All homes—regardless of their zone—should be tested.

Slide 3-3 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 3-4 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 3-5 Where radon comes from Uranium-238 Thorium-234 Thorium-230 Radium-226 Radon-222 Protactinium-234 See handout 3-1

Slide 3-6 Sources of radon Soil and rock: most common source Groundwater Building materials containing uranium and radium

Slide 3-7 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 3-8 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 3-9 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 3-10 Radon in small, closed groundwater systems 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 3-11 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 3-12 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 3-13 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 3-14 Questions? About radon sources Next –Mechanisms that transport radon into a home

Slide 3-15 Radon transport mechanisms Push or pull radon into a home

Slide 3-16 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 3-17 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  Warm air  Negative pressure  Soil gas  (including radon)  

Slide 3-18 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 3-19 Air pressure differences Environmental effects Weather –Seasons –Rain, snow, and frost –Wind Other factors that seal the soil around a home

Slide 3-20 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 3-21 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 3-22 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 3-23 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 3-24 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 3-25 Environmental effects Factors that seal the soil Asphalt or concrete driveways Concrete patios Prevent radon from escaping into outdoor air

Slide 3-26 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 3-27 Other radon transport mechanisms 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 Higher radon  concentration  Lower radon concentration  Diffusion = movement through materials

Slide 3-28 Radon Other radon transport mechanisms Emanation 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 3-29 Other radon transport mechanisms Outgassing Outgassing = release of radon gas from water

Slide 3-30 Questions? About mechanisms that transport radon into a home Next –Pathways that allow radon to enter a home

Slide 3-31 Radon pathways into the home Natural –Pores or empty spaces in soil –Cracks in underlying rocks –Earthen areas in basements Artificial –Fill below foundations –Trenches for utility lines and plumbing –Water drainage systems –Other openings in foundations

Slide 3-32 Pathway characteristics Ease with which air moves through the pathway Distance from radium (radon source) Connections with other pathways

Slide 3-33 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 3-34 Radon levels vary in space 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 3-35 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 3-36 Why this information matters Air pressure differences Ventilation Environmental effects Procedures for measuring radon are designed to control for these factors:

Slide 3-37 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 3-38 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 3-39 Summary How radon enters a home

Slide 3-40 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 3-41 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 3-42 Questions About how radon enters a home

Slide 3-43 Check your understanding See handout 3-4