International Conference on Occupational Radiation Protection: Enhancing the Protection of Workers – Gaps, Challenges and Developments Vienna, Austria, 1-5 December 2014 Practical implementation of anticipated radon dosimetry changes in the mining industry Ches Mason Manager Radiation Governance BHP Billiton Olympic Dam Views expressed in this presentation are those of the author alone and may not be construed as having any bearing on those of his employer.
Assessing doses from radon Radiation exposure in a mine Radon Decay Product (RDP) exposure is measured in terms of dust from PAEC (Potential Alpha gamma ore Energy Concentration) from handling in (mJ m -3 ) and time. radon ore from body 222 Rn exposure is ore body measured in terms of activity concentration in (Bq m -3 ) and time. Effective dose is calculated from a Currently: DCF = 1.4 mSv per (mJ h m -3 ) recommended dose conversion factor (DCF) Slide 2
Why the change? Epidemiology ICRP 60 and 65 ICRP 103 and 115 Radon risk: Radon risk: 8 x 10 -5 per (mJ h m -3 ) 8 x 10 -10 per (Bq h m -3 ) Effective dose risk: Effective dose risk: 5.6 x 10 -5 per mSv 4.2 x 10 -5 per mSv Equating risks: Equating risks: DCF: 1.4 mSv per (mJ h m -3 ) DCF: 3.4 mSv per (mJ h m -3 ) Increase: 2.4 times (Dose conversion convention) Dosimetric modelling Statement on Radon † DCF: 3.0 mSv per (mJ h m -3 )* Increase: 2.2 times (Dose coefficient) † Move to dosimetric modelling * Draft OIR Part 3 – for mines Slide 3
What to do? Need for review: Assess effective doses using the new DCF; Review the adequacy of the dose assessment program; Review the optimization of protection of the workforce; and If necessary, take action to reduce exposure to radon. Anticipate the change: Be prepared: all of the above can be assessed in advance; Engage with the workforce: explain what is likely to happen; Engage with the regulatory body: agree on the strategy; and If necessary, source equipment suppliers and service providers, and develop drafts of new procedures. Slide 4
Review dose assessment Greater accuracy needed? Does the current procedure make conservative assumptions which could be reduced? For example, is time in air-conditioned cabins taken into account? Will some (or more) workers need to be assessed through personal monitoring? If doses are high, is characterization of the mine atmosphere needed? For example, would amendment of the DCF for particle size be implied? Note that dose records will need to include the DCF used. Slide 5
Discourage smoking! Nominal risks* from natural background and from 0.5 µJ m -3 at work Risk/y (x 10 -4 ) Non-smoker Risk/y (x 10 -4 ) Non-smoker Risk/y (x 10 -4 ) Regular smoker 7 7 7 6 6 6 5 5 5 4 4 4 3 3 3 2 2 2 1 1 1 0 0 0 *risk coefficients from ICRP103 and ICRP115; cosmic, terrestrial and ingestion global average doses from UNSCEAR 2008; radon: 50 Bq m -3 at home, 0.5 µJ m -3 at work; approximate non-smoker risk (avg /6) and regular (>25 cig/day) smoker risk (avg x5). Slide 6
Optimize protection Do the changes imply a need to reduce exposure? E.g. Could the most exposed workers exceed dose constraints? Review mine ventilation, especially underground. E.g. More clean air? (Watch out for unattached fraction.) Are there sources that can be better controlled? E.g. Dewatering? Control of other pathways? Apply engineering controls where possible. E.g. Air-conditioned cabins on mobile equipment. Automation/robotics? Apply administrative controls. E.g. Review reference levels for mine clearance, etc. Use personal protective equipment. E.g. Respirators, filtered-air hardhats. Slide 7
Increase in assessed doses Dose constraint exceeded? Dose limit exceeded? 160 Number of workers 140 120 100 80 60 40 20 0 0 2 4 6 8 10 12 14 16 18 20 22 24 Annual effective dose (mSv) Slide 8
Optimize protection Do the changes imply a need to reduce exposure? E.g. Could the most exposed workers exceed dose constraints? Review mine ventilation, especially underground. E.g. More clean air? (Watch out for unattached fraction.) Are there sources that can be better controlled? E.g. Dewatering? Control of other pathways? Apply engineering controls where possible. E.g. Air-conditioned cabins on mobile equipment. Automation/robotics? Apply administrative controls. E.g. Review reference levels for mine clearance, etc. Use personal protective equipment. E.g. Respirators, filtered-air hardhats. Slide 9
Engineered controls Some Air-conditioned examples cabins After Before Slide 10
Optimize protection Do the changes imply a need to reduce exposure? E.g. Could the most exposed workers exceed dose constraints? Review mine ventilation, especially underground. E.g. More clean air? (Watch out for unattached fraction.) Are there sources that can be better controlled? E.g. Dewatering? Control of other pathways? Apply engineering controls where possible. E.g. Air-conditioned cabins on mobile equipment. Automation/robotics? Apply administrative controls. E.g. Review reference levels for mine clearance, etc. Use personal protective equipment. E.g. Respirators, filtered-air hardhats. Slide 11
The particle size issue ICRP126: use the default RADEP96 HPA2012 DCF! 160 DCF (dosimetric modelling; mSv/WLM) 150 140 Theoretically, the DCF 130 120 may need to be modified 110 to take account of mine air 100 90 characteristics, such as 80 particle size. 70 60 50 Note: filtering out radon 40 decay products may also 30 20 reduce the concentration 10 of nucleation sites, 0 0.1 1.0 10.0 100.0 1000.0 10000.0 resulting in a higher AMTD/AMAD (nm) unattached fraction. ‘unattached’ | ‘attached’ Slide 12
Planned vs. Existing Exposure Situations Mines currently treated as existing exposure situations Review the radon reference level value: decrease by 2? Continue to optimize protection below the new reference level. If not possible, consult with the regulatory body: the requirements for planned exposure situations may need to be applied. Mines regulated as planned exposure situations (summary) Review dose assessment and optimization of protection. Minor improvements, as outlined, are likely to be adequate to continue to meet regulatory requirements. In some cases of high radon or RDP concentration, The significant reduction of exposure may be needed. end of the world Slide 13
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