Lesson 3 How does radon enter a? Radon in the For most Americans, greatest exposure to radon is in, 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 Old or new Drafty or well sealed With or without a basement Slide 3 1 Importance of testing Even neighboring s may have very different radon levels EPA recommends that all s be tested for radon Testing is the only accurate way to determine the radon level in any Slide 3 2 2006 3 1
Requirements for radon to enter a 1. A source of radon 2. A mechanism to transport radon from the source into the 3. An opening or pathway into the Slide 3 3 Level of radon in a Depends on Strength of radon sources: most important factor Distance of the sources from the Ease of transport into the Ventilation in the Environmental factors Slide 3 4 Where radon comes from Uranium 238 Thorium 234 Protactinium 234 Thorium 230 Radium 226 Radon 222 See handout Slide 3 5 3 1 2006 3 2
Sources of radon Soil and rock: most common source Groundwater Building materials containing uranium and radium Slide 3 6 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, they can be source of radon Uranium decays into radium Radium decays into radon Slide 3 7 Overview Radon from soil and rock Radon enters soil gas Soil gas moves from ground into air in Usually enters through foundation Cracks in walls and floors Drains Sump holes Dirt floors Construction joints Spaces around service pipes Slide 3 8 2006 3 3
Radon source Groundwater Usually a problem only in small, closed water systems Where underlying rocks contain high levels of uranium Where s rely on groundwater from private wells or small public waterworks as the main water source Slide 3 9 Radon from groundwater sources Radon does not have time to decay into harmless byproducts before entering a Once inside the, radon escapes from the water into the air during normal household activities: Showering Washing clothes or dishes Flushing toilets Slide 3 10 Radon in other water Usually not a problem where s Use surface water (lakes, streams, rivers, and reservoirs) Radon usually escapes into air before it reaches a 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 Slide 3 11 2006 3 4
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 12 Strength of radon sources Even s next to each other may have different radon sources, with different strengths. Rock: strong radon source Groundwater containing radon Rock: strong radon source Rock: moderate radon source Soil: moderate to weak radon source Slide 3 13 Questions? About radon sources Next Mechanisms that transport radon into a Slide 3 14 2006 3 5
Radon transport mechanisms Push or pull radon into a Air pressure differences Diffusion Emanation Outgassing Diffusion (1 4%) Average contribution to radon in a Emanation (2 5%) Outga ssing (less than 1%) A ir pressure diffe rences (85 90%) Slide 3 15 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 16 Air pressure differences Stack effect Heated indoor air rises and escapes through cracks and holes at top of Creates positive air pressure at top of 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 17 2006 3 6
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 18 Air pressure differences Environmental effects Weather Seasons Rain, snow, and frost Wind Other factors that seal the soil around a Slide 3 19 Environmental effects Seasons Usually more radon enters in winter 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 Slide 3 20 2006 3 7
Complex effects of good ventilation (open windows) Reduces vacuum effect Generally reduces radon entry Dilutes radon in 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 21 Complex effects of good ventilation (open windows) Reduces vacuum effect Generally reduces radon entry Dilutes radon in But may also increase stack effect Thereby increases radon entry When you measure radon in short term tests, windows must be kept closed Slide 3 22 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 Slide 3 23 2006 3 8
Environmental effects Wind Don t measure radon during high winds because results may not show typical levels. Higher pressure upwind Wind Lower pressure downwind Downwind draft effect Changes pressure around the Higher pressure in soil as wind pushes beneath soil Slide 3 24 Environmental effects Factors that seal the soil Prevent radon from escaping into outdoor air Asphalt or concrete driveways Concrete patios Slide 3 25 Summary Air pressure Main mechanism that brings radon into a 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 26 2006 3 9
Other radon transport mechanisms Diffusion = movement through materials Lower radon concentration Higher radon concentration 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 Slide 3 27 Other radon transport mechanisms Emanation = emission of gas from a surface by radioactive decay Some rocks and other building materials contain uranium or radium 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 Radon Radon Radium Uranium Slide 3 28 Other radon transport mechanisms Outgassing = release of radon gas from water Slide 3 29 2006 3 10
Questions? About mechanisms that transport radon into a Next Pathways that allow radon to enter a Slide 3 30 Natural pathways Radon pathways into the 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 31 Pathway characteristics Ease with which air moves through the pathway Distance from radium (radon source) Connections with other pathways Slide 3 32 2006 3 11
Review Requirements for radon entry 1. Radon source 2. Mechanism to transport radon from source into 3. Pathways into the These factors determine the amount of radon that enters a. Slide 3 33 Radon levels vary In space From geographic area to geographic area From to From level to level within a Usually highest in lower levels of Higher readings in upper levels suggest unusual radon entry factors Slide 3 34 Radon levels vary Over time In time From season to season From day to day From hour to hour With changes to the (such as additions) Factors Air pressure changes Wind speed and direction Indoor and outdoor temperature changes Rain, snow, and frost Use of mechanical exhaust systems Because radon levels vary, testing must be done over a period of time Slide 3 35 2006 3 12
Why this information matters Procedures for measuring radon are designed to control for these factors Air pressure differences Ventilation Environmental effects Slide 3 36 Summary Every should be tested for radon Requirements for radon to enter a Radon source Mechanism to transport radon Pathway See handout 3 3 Slide 3 37 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 Slide 3 38 2006 3 13
Summary How radon enters a Slide 3 39 Activity For a hypothetical client, summarize how radon enters a Importance of testing every Factors that determine the radon level in a Most common sources of radon Common mechanisms of radon entry Pathways into the Variations in radon levels over space and time Hypothetical client: an attorney Slide 3 40 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 41 2006 3 14
Questions About how radon enters a Slide 3 42 Check your understanding See handout 3 4 Slide 3 43 2006 3 15