Radon Gas & What You Need to Know. Bob Caskanette, B.A.Sc., CEC, CAQS, CRS, CIEC, C.E.T., EP (C-NRPP Certified) Caskanette Udall Consulting Engineers

Transcription

1 Radon Gas & What You Need to Know Bob Caskanette, B.A.Sc., CEC, CAQS, CRS, CIEC, C.E.T., EP (C-NRPP Certified) Caskanette Udall Consulting Engineers

2 What is Radon? Naturally occurring radioactive soil gas colourless & odourless Produced by the breakdown of Uranium in soil, rock, and water Colourless and odourless 2nd leading cause of lung cancer deaths in the US & Canada after smoking Leading cause of lung cancer in Canada for non-smokers (~16% of total) Largest environmental cause of lung cancer (3200 per year in Canada) Found in all areas of the world at varying levels Only testing will identify concentration within a building 2

3 Chemistry Refresher Element #86 on periodic table of elements (Rn) Atomic weight 222 (86 Protons+136 Neutrons) Often expressed as Rn 222 (Isotope) Passes through most filters, adsorbs to charcoal Noble gas - non-reactive chemically Carcinogen (causes cancer) Heavier than air tends to sink 3

4 Half Life of Radon Rn-222 has half life of days Half-life is time required for half of the atoms in radioactive element to decay In 3.8 days, you will have half as much Rn In another 3.8 days, half as much again Continues forever and never reaches zero Typically after 10 half lives, quantity is however considered zero Decays into other Radon Decay Products (RDPs) Mainly concerned with RDPs - PO-218 and PO-214 4

5 Types of Radiation Non-Ionizing radio waves, infrared, visible light Ionizing alpha, beta, gamma rays and X-rays; ability to produce ions Radioactivity result of instability in energy relationships between protons, neutrons and electrons that make up atom Rn mainly emits ionizing alpha particles 5

6 Radon Decay Chain 6

7 Mechanism of Lung Cancer Radon and RDP s breathed in Some Radon exhaled RDP s remain stuck to lung tissue PO-218 and PO-214 emit alpha particles Alpha particles strike lung cells Causes physical or chemical damage to DNA Can lead to lung cancer 7

8 Radiation Sources Data as per World Nuclear Association February

9 Radon Potential Map 9

10 How does Radon Enter Homes? 10

11 Main Source of Radon Soil Gas 11

12 Radon Measurement Guidelines Radon measured in Becquerels (Bq) in Canada Expressed as Bq/m 3 (1 m 3 = 1000 L of air) Maximum allowable indoors is 200 Bq/m 3 Avg. indoor = 45 Bq/m 3 & outdoor = 10 Bq/m 3 USA uses Curies, expressed as picucurie per litre (pci/l) To convert, divide Bq/m 3 by 37 for pci/l Example: 200 Bq/m 3 /37 = 5.4 pci/l US Standard is lower at 4 pci/l (148 Bq/m 3 ) Additional requirements for mining industry 12

13 When and How Long to Test? Should be long term test of at least 3 months (91 days) Sometimes short term tests are done (min. 48 hours), then long term tests are followed up (schools, real estate deals, etc.) Best to do in winter months if possible (highest concentrations) since doors/windows are closed, snow cover etc. Measurement device should have tamper proof protocols in place (tilt/movement sensors, special seal tapes, locks, etc.) Test lowest level occupied for at least 4 hours/day 13

14 Measurement Devices Electret Ion Chamber (EIC) - E-PERM (Electret Passive Environmental Radon Monitor) - Electret surface is Teflon disc with positive static charge. Attracts negative ions from Radon decay in ion chamber which is measured by voltage drop at sample collection time. Sample time from 2 days to 1 year. 14

15 Measurement Devices Alpha Track uses plastic chip to record alpha energy damage tracks Lab etches surface to reveal damage pits Can be stored as permanent record Minimum 1 month test 15

16 Measurement Devices Activated Charcoal adsorbs Radon (only for short term tests of ~2-7 days) Affected by temperature, air currents and humidity Air current and higher temperatures can produce higher results than actual Can be: Open Face Diffusion Barrier Bags or Vials (liquid scintillation) type 16

17 Measurement Devices Continuous Radon Monitor direct read instrument, typical for shorter term tests Can be many types: solid state with ion chamber, pulse ionization chamber or scintillation cell instrument Requires computers for setup & to produce reports 17

18 Measurement Devices Digital Detectors plugs into standard wall outlet Continuous display of past 7 days or since turned on Homeowner use only Alarms if high levels Rn Not suitable for professional use 18

19 Measurement Devices Continuous Working Level Monitors Measures Radon decay products (working levels) to measure direct health risk Not very common other than in mining Miners at higher risk of lung cancer due to more increased exposures to Radon 19

20 When to Mitigate? Mitigation needed when above 200 Bq/m 3 Cannot be determined by short term test If Bq/m 3, remediate within 2 years Above 600 Bq/m 3, remediate within 1 year Radon cannot be completed eliminated, should be reduced to as low as reasonably achievable (ALARA) 20

21 Radon Mitigation Intro Active sub-slab depressurization most effective and most common 21

22 Radon Mitigation Sump-hole depressurization sump capped and sealed, variation of sub-slab depressurization Drainage system depressurization homes with drain tiles or perforated pipe to drain water away; suction placed on tiles or pipes to draw Radon away from homes; good for block wall foundations especially 22

23 Radon Mitigation Active sub-membrane depressurization good for homes with soil crawlspaces; uses thick plastic (polyethylene) membrane over soil, sealing air tight to foundation walls and placing pipe with fan to draw Radon out and vent to outdoors; good seals around pipes/soil are critical 23

24 Radon Mitigation Assessing building pressure differentials negative building pressure will draw more Radon gas in Sealing major entry routes sump pits, floor drains, cracks in poured foundation walls and floor slabs, floor/wall joints, voids in block walls Covering exposed soils with plastic membrane Increasing mechanical ventilation in homes dilutes and reduces Radon levels Can be assisted by Heat Recovery Ventilators (HRV s) or Energy Recovery Ventilators (ERV s) 24

25 Testing and Mitigation Radon re-test should be performed at least 24 hours after fan for mitigation system is turned on Should be done in same place as previous test Should have long term re-test intervals established Consultants and contractors should be Canadian National Radon Proficiency Program (C-NRPP) trained and certified to undertake testing or mitigation Only testing can identify Radon concentrations in a building Will be different in every building, cannot rely on use of maps or comparisons to neighbouring homes and buildings 25

26 New Construction Cannot predict prior to construction whether new home will have high Radon levels 2010 National Building Code (NBC) includes requirements to address Radon Parts 5 and 6 requires engineers and designers consider Radon protection in their designs Part 9 includes consolidating air barrier requirements (sealed plastic membrane under foundation slab), granular fill needed under slab and rough-in for future radon reduction system Provinces have or will soon be adopting 2010 NBC Some cities have mitigation programs which requires new buildings undergo mandatory or voluntary testing 26

27 More Information Radiation Protection Bureau Health Canada - -Phone: Province of Ontario - -Toll free: Health Canada Website C-NRPP ; 27