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Investigation of Radon Decay Products: Case Studies and Review of Key Scientific Literature

This presentation explores the background of radon decay products (RDPs), important factors related to their inhalation and potential lung damage, and a literature review of key scientific studies. Two case studies are presented, along with recommendations and an opportunity for questions.

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Investigation of Radon Decay Products: Case Studies and Review of Key Scientific Literature

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  1. Investigation of Radon Decay Products: Case Studies and Review of Key Scientific Literature Lisa Gregory, PhD AARST Symposium October 2, 2018 2018 International Radon Symposium™

  2. Outline • Radon Decay Product (RPD) Background • Important Factors • Alpha Particles • Working Levels • Literature Review • Case Study 1 • Case Study 2 • Summary • Recommendations • Questions 2018 International Radon Symposium™

  3. Radon Decay Product Background Half Life Radon-222 • RDPs come from the radioactive decay (“breakdown”) of radon gas. • A portion of these RPDs “plate out” and attach to surfaces and are not inhaled. • The other portion of these RDPs stay suspended in the air and may be inhaled. • Some inhaled RDPs release alpha particles in lungs that can damage lung tissue and cause cancer. 3.8 Days αγ Polonium-218 3 Minutes αγ Lead-214 27 Minutes βγ Bismuth-214 19.7 Minutes βγ Polonium-214 .0096 Seconds αγ Lead-210 19.4 Years 2018 International Radon Symposium™

  4. Important Factors • The potential that someone may experience damage to lung tissue by an alpha particle is directly related to the amount of suspended RDPs that are inhaled and reach the lung tissue. • Once RDPs adhere to lung tissue, the probability that irreparable damage may occur increases with: • Shorter half-life • Higher energy alpha particles • Thinner protective layer of lung surface epithelial cells • Lower genetic resilience • Random: It’s only by chance whether the alpha particle hits the DNA of a sensitive cell and causes damage. 2018 International Radon Symposium™

  5. Alpha Particles are the “Bad Guys” 2018 International Radon Symposium™

  6. Alpha Particles are the “Bad Guys” DNA • Mucus layer (~10 microns thick) • Epithelial layer (40-80 microns thick) • Basal epithelial cells frequently divide and are sensitive to development of cancer • Alpha particles with higher energy penetrate further and have greater probability of causing double strand DNA breaks • DNA double strand breaks are hard to repair α 2018 International Radon Symposium™

  7. RDP Equilibrium Factor • The Equilibrium Factor (EF) is the ratio of suspended RDPs to the total RDPs produced by radon gas. • EFs were originally determined by uranium mining studies that measured both radon and RDP working levels (WL). • Different organizations assume different EFs. • Currently, the EPA and World Health Organization assume an EF of 40%. 40% • Airborne • Breathable • Measureable Radon-222 RDPs • Plated Out • Not Breathable • Not Measurable 60% 2018 International Radon Symposium™

  8. Equilibrium Factor Assumptions EF = 0.4 EF = 1.0 EF = 0.5 50% Suspended Past EPA protocol 100% Suspended OSHA assumption 40% Suspended Current EPA protocol World Health Org. 2018 International Radon Symposium™

  9. Working Level (WL) • RDPs concentration measured in WL is a true measure of actual exposure to radiation • WL was developed in the 1950s and is commonly used to measure RDP exposure by underground miners • One WL refers to the concentration of RDPs in equilibrium with 100 pCi/L of radon • A WL of 0.02 is referred to in U.S. law as the “not to exceed” radiation level • Radon levels are not accurate measures of exposure to radiation and the guidance of 4.0 pCi/L is not in codified in law 2018 International Radon Symposium™

  10. 2018 International Radon Symposium™

  11. Literature Review 2018 International Radon Symposium™

  12. AARST Protocol (2014) • AARST and EPA used to have more information regarding RDPs. This information was removed for awhile. • The most recent AARST protocol has included RDP measurement info. • Current protocol tells how RDPs can be used to further characterize home and room conditions. • Says that RDP measurements alone do not tell you everything and cannot be solely used to assess mitigation needs. 2018 International Radon Symposium™

  13. Seasonal Behavior of RDPs (2014) • Essential to characterize attached vs. unattached RDPs • Observed highest RDP dose during winter and lowest during Spring • We see similar seasonal findings between RDP dose and radon concentration • Due to seasonal differences of aerosol particle sizes and RDP dose 2018 International Radon Symposium™

  14. Deposition of Radon Progeny (1997) • Investigates the concept of RDP plate-out and the use of different deposition models • Homogeneous turbulence model • Higher fan speeds increase air turbulence and therefore RDP deposition rates • Changes in air temperature can also cause mixing and higher deposition rates • Concluded that increased air circulation lowered working levels, thereby lowering EF 2018 International Radon Symposium™

  15. Effect of Air Cleaners on Radon Progeny (1996) • Suggests there are three main ways to control RDPs • Prevent radon infiltration • Dilute radon/RDPs inside the house • Directly remove RDPs • Utilized a model to reflect nasal/oral RDP deposition • Most air cleaners alone are insufficient to reduce RDPs • They can greatly reduce aerosols • Combination of air movement and air cleaners can work well in reducing RDPs 2018 International Radon Symposium™

  16. Case Studies 2018 International Radon Symposium™

  17. Lowering RDP Risk • The primary goal of radon mitigation is to reduce Radon Decay Product (RDP) exposure. • Reduce radon gas concentration (“source” method) • Direct reduction of RDPs (“direct” method) • Methods for lowering RDPs that do not affect radon gas concentrations include: • Increasing air circulation • Increasing air filtration • These methods can be useful for areas that are unsuitable for traditional radon mitigation techniques. 2018 International Radon Symposium™

  18. Study Descriptions • “Mini” studies were performed in two separate rooms at a military installation after short-term radon tests resulted in elevated radon levels. • Studies investigated effects of HVAC or air filtration/ movement on radon and RDPs. • Purpose of these studies were to investigate radon and RDPs in response to variable conditions and to determine effectiveness of HVAC alterations as a radon mitigation approach. 2018 International Radon Symposium™

  19. Office X • First floor office located over slab on grade. • Initial short-term test showed radon was elevated compared to adjacent rooms. • Office X: 12.3 pCi/L • Adjacent rooms: <4.0 pCi/L • Each office had its own HVAC unit located on exterior wall. • We were told the HVAC unit was plumbed to fresh air. • We were told that occupant sometimes turned off his HVAC unit. 2018 International Radon Symposium™

  20. Office X: Case Study 1 We measured continuous radon and continuous RDPs with HVAC ON for two days and then OFF for two days. This study ran from Wednesday December 6th to Monday December 11th 2017. If the HVAC is bringing fresh air into the room, then when the HVAC is ON ___________________________________. • Radon and RDPs will increase • Radon and RDPs will decrease • Radon and RDPs will remain the same • Radon and RDPs will have variable responses Hypothesis 1: 2018 International Radon Symposium™

  21. Office X: Case Study 1 Hypothesis 2: If the assumed equilibrium factor of 50% is correct, then an increase of radon over 4 pCi/L will be associated with an RDP level ___________ than 0.02 WL. • greater • lower • the same as • impossible to predict 2018 International Radon Symposium™

  22. Office X: Case Study 1 Results

  23. Office X: Case Study 1 Conclusions: • HVAC was NOT bringing fresh air into office. • HVAC seemed to be “mining” radon gas from under slab. Investigate HVAC! • RDPs were way under the action level of 0.02 WL even with radon concentrations almost at 8.0 pCi/L. • Actual EF was much lower than assumed EF when HVAC ON. Action Item? Why? Because increased air circulation from the HVAC fan was causing more RDP plate out to surfaces!

  24. Office X: Investigate HVAC Fresh air intake blocked!

  25. Unit Ventilator pulling soil gas into unit! Air gap to soil!

  26. Office X Solution: • Unblock air intake • Seal opening • Retest using CRM SOLUTION WORKED! Radon was reduced to 0.9 pCi/L with HVAC ON! 2018 International Radon Symposium™

  27. Room Y • Small, basement room with smaller sublevel accessible through door that typically stays open. Room unsuitable for traditional mitigation.

  28. Case Study 2: Room A37 • Results support the idea that RDP reduction is possible through increased air flow and filtration • Working levels were much lower than expected given radon concentration and assumed EF • If RDPs and radon were analyzed together, invasive mitigation may not be needed

  29. Room Y: Case Study 2 Measure continuous radon and continuous RDPs for two days under normal conditions and then with fan and filters ON for four days. Study ran from Monday with HVAC ON for two days and then OFF for the rest of the trial. Study ran from Monday 26 February to Monday 3 March 2018. If air filtration and circulation increase RDP plate out, then RDP measurements will _____________________. • increase • decrease • exhibit no change Hypothesis 1: 2018 International Radon Symposium™

  30. Room Y: Case Study 2 Hypothesis 2: When fan/filter are OFF, if there are relatively high radon levels than RDPs should be relatively ____________. • high • low • no different 2018 International Radon Symposium™

  31. Room Y: Case Study 2 Power-on Power-out

  32. Room Y: Case Study 2 Conclusions: • Power outage resulted in reduction of negative pressure in room as evidenced by greatly reduced radon levels. • Room has definite radon issue (space is under negative pressure). Action Item? Investigate HVACs! • Air filter/movement reduced RDPs to below detectable levels (similar to the air outside) even in the presence of high radon levels. • Room conditions are extremely amenable to RDP plate out. Why? Very large surface to volume ratio and the air movement from ceiling unit.

  33. Room Y Investigations

  34. Takeaways from these studies • HVAC investigation/alteration is a cheap radon mitigation technique that can work to fix radon issues in work spaces. • The military has spaces that are not suitable for traditional mitigation techniques, which are often costly and require penetrations through floors and/or walls. • Consider measuring RDPs and using air movement/ filtration as a relatively cheap and easy technique to ensure the space poses no risk even in the presence of radon levels above 4.0 pCi/L. • Consider measuring RDPs as a standard practice in any space with high radon levels just to confirm the RDP WLs. We have had difficulty finding a space with RDP WL even close to 0.02 WL. Showing low WLs can protect the office owner against possible litigation. 2018 International Radon Symposium™

  35. Recommendations 2018 International Radon Symposium™

  36. Questions? 2018 International Radon Symposium™

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