Proceedings of the 2006 International Radon Symposium September 17 - 20,2006 IN SITU AIRBORNE RADON MONITORING FOR STANDARDS COMPLIANCE WITH OSHA-NRC-EPA P. ~ a ~ a m and' P. 11a2 ~ e ~ a r t m eof n tPhysics, University of Guelph, Guelph, ON, N I G 2W 1, Canada, The NORM ~ r o u5~Maplewood , Drive, Guelph, ON, N I G 1L9, Canada, Email: pjagam@uoguelph.ca, jagam@thenormgroup.ca ~ e ~ a r t m eofn tEarth Atmospheric and Planetary Sciences, Massachusetts Institute of Technology, Cambridge, MA 02 139, U. S. A. The NORM Group Organization, Cambridge, MA 02139, U. S. A. Email: pila@mit.edu, ila@thenormgroup.org ABSTRACT In situ radon monitoring is necessary to characterize and qualify workplace and other environments in order to determine the need for occupational exposure assessments, to demonstrate compliance with standards and to verify the effectiveness of mitigation efforts. A web-based, energy sensitive electrostatic chamber radon monitoring system, developed at the University of Guelph, can be used to accomplish such occupational and environmental monitoring needs. This presentation illustrates the application of this monitoring system to radon monitoring challenges such as dynamic surveillance to define restricted "airborne radioactive areas", assessing the need for radon exposure monitoring of workers via real-time radon concentration measurements, and performing this monitoring INTRODUCTION Exposure to high concentrations of radon and radon decay products correlated with the incidence of lung cancer in several groups. In the United States of America (USA), National Research Council's report of the sixth Committee on Biological Effects of Ionizing Radiations (BEIR VI) addresses the risk of lung cancer associated with exposure to radon and its radioactive progeny [I]. Many countries around the world adopted the limits of exposure recommended by the International Commission on Radiological Protection (ICRP) [2] at the national and regional level. Accordingly, in USA the regulations and guidelines are provided by Nuclear Regulatory Commission (NRC), and federal agencies such as Occupational Safety and Health Administration (OSHA), Environmental Protection Agency (EPA), Department of Energy (DOE), and Agency for Toxic Substances and Disease Registry (ATSDR) [3-61. Seasonal variations were reported at above ground locations around the world with maximums occurring at different times of the year at different locations. Since radon concentration in air is dependent on the ventilation parameters, variations can be readily Copyright 0 2007 by the American Association of Radon Scientists and Technologists, Inc. www.aarst.orq 21 Proceedings of the 2006 International Radon Symposium September 17 - 20,2006 detected in the surface buildings as well as at underground sites. Depending on the ventilation at the underground location, the measured radon concentrations and working level values fell in different ranges stated by the regulatory authorities. Different monitoring schedules are then required in the different ranges of measured values in order to meet the recommendations of ICRP, and the regulations issued by the national and the regional regulatory agencies. The Environmental Protection Agency (EPA) in USA identified that the continuous monitoring of radon is the most accurate method of measuring the actual radon exposures. Continuous monitoring of radon and radon decay products aids in optimization of compliance efforts, and in recording actual occupational exposure levels. Remedial actions can then be justified based on recorded data and compliance can be demonstrated in real-time. For the purpose of developing policy for the radiation protection of the public, there is a need to measure and characterize the possible risks across the range of exposures received by the population. The higher end of that range of exposures is comparable to those exposures that caused lung cancer in underground miners. The lower end of that range includes exposures received from an average indoor lifetime exposure, which is at least one order of magnitude lower. For many years in USA, radiation, even at low levels, was considered to present some risk to health. This risk model is referred to as the "linear, no-threshold (LNT)" hypothesis. Over the years, successive scientific studies have been done resulting in publication of the Biological Effects of Ionizing Radiation (BEIR) reports. Recent studies have led to an increasing debate whether the LNT model is appropriate. In this context, high sensitivity continuous monitoring of radon aids in optimization of compliance efforts and in recording actual exposure levels at the low end of the exposure range. The present work reports on the use of the Sabre-system developed at the University of Guelph for the continuous monitoring of radon concentrations in air simultaneously with the working level values for the radiation protection of the workers and the public from the point of view of compliance with ICRP Recommendations. REGULATIONS AND GUIDELINES ICRP Publication 35 [7] discussed the general principles of monitoring for radiation protection of workers. ICRP Publication 37 [a] examined the same from the point of view of a cost-benefit analysis in the optimization of radiation protection. The radiation protection standards for all DOE workers are described in 10 CFR 835. The Occupational Safety and Health Administration's (OSHA) standard for ionizing radiation can be found in 29 CFR 1910.1096. The permissible radiation exposure levels are contained in Table G-18 of the standard. Some pertinent regulations are quoted below in Tables 1 and 2 for the sake of illustrating the salient points in the present work. Copyright 0 2007 by the American Association of Radon Scientists and Technologists, Inc. www.aarst.org 22 Proceedings of the 2006 International Radon Symposium September 17 - 20,2006 Table 1. Occupational Standards and Regulations for Radon [6] Organization Pertinence Level Notes 1 WLM */year Advisory; National Institute for Occupational Occupational Safety and Health (mining) exposure limit and ALARA' Occupational Safety and Health occupational 4 WLMJyear Regulation Administration Mine Safety and Health Mining 4 WLMJyear Regulation Administration American Conference of 4 WLWyear radon Advisory daughters for Governmental Industrial Occupational Hygienists *WLM (Working Level Month): a unit of measure commonly used in occupational environments. 'ALARA: As Low As Reasonably Achievable. Table 2. Radon-222 [9] I Occupational Values 1 I Radionuclide Radon-222 , Category 1 With daughters removed 1 Ingestion ALI (uCi) With daughters present - - 3-. Inhalation ALI DAC (pCi) (pCi/ml) lE+4 1 4E-6 level) ALI: Annual Limit on Intake DAC: Derived Air Concentration HIGH SENSITIVITY CONTINUOUS MONITORING WITH SABRE SYSTEM The Sabre detector system was designed for continuous monitoring of radon and radon progeny in the ambient room air with high sensitivity and high precision, and display the results on the Internet based World Wide Web (web) automatically in real time. The high sensitivity design was based on the earlier design of a Guelph Electrostatic Chamber (ESC)reported by Wang et a1 [lo]. Jagam and Simpson [ l 11 reported the early results obtained with the Sabre-system for the continuous monitoring of radon at a typical workplace. Copyright 0 2007 by the American Association of Radon Scientists and Technologists, Inc. 23 www.aarst.org Proceedings of the 2006 International Radon Symposium September 17 - 20,2006 Alpha-ray energy spectrometry of the decay products of radon (Radon 2 2 2 ~and n Thoron Rn) from the ambient air by electrostatic precipitation on to a PiN diode is the basic principle by which radon concentrations and working level (WL) values were determined by this system. Air was continuously monitored in a well-defined sensitive volume of the detector. The sensitive volume of the detector was not isolated from the room in any way, and was an integral part of the room because of diffusion. Digital data were sent at preset time intervals over the Internet to a server. The server displayed the time variation of the data as an X-Y plot available on the World Wide Web (Web). The data were also stored locally on the personal computer. 220 The focus in the continuous monitoring of radon was on the variations in the concentration of radon with time. When all other conditions remained the same, the radon concentration measured by the Sabre-system remained the same. The time variation of radon concentration should be zero under these conditions in ambient air as monitored by the system. RADON CHARACTERIZATION OF WORK ENVIRONMENTS Variation in the measured concentration of radon at an above ground location in Sudbury ON, Canada, is shown in Figure 1 over a period of approximately three years. The breaks in the data collection resulted from equipment down time and 1 or changes in the priorities assigned to the data collection at that time. Run lime (h) Figure I . Variation of the concentration of radon over a period of three years at an above ground location in Sudbury, ON, Canada. Copyright 0 2007 by the American Association of Radon Scientists and Technologists, Inc. www.aarst.orq 24 Proceedings of the 2006 International Radon Symposium September 17 - 20,2006 Variations of nearly an order of magnitude can be clearly seen in Figure 1. The maximums in the variation of the concentration of radon occur in the spring in each year at this location. Also, because of the energy spectrometry capability of the Sabre-system, the two polonium progeny (^PO and ^PO) of ^ ~ nwere monitored independently of each other. The variation of the ratio of 2 ' 8 ~ and o ^PO was found to be constant within experimental errors, and confirms the variation in time independently at this above ground location. Variation in the measured concentration of radon at an underground industrial location is shown in Figure 2 over a period of one year. The breaks in the data collection resulted from equipment downtime and 1 or changes in the priorities assigned to the data collection at that time. The variation in the concentration of radon was found to be a lot less than at the above ground location over the period of one year except for a systematic shift over a one month period. The shift was caused by changes in the ventilation due to changes in operational parameters of the ventilation system. The ratio of the two polonium progeny (^PO and ^PO) was found to be much more variable underground than above ground. The variations in humidity and temperature were found to be constant to within 5% over the entire period, and were not sufficient to produce the observed . the ratio of the polonium progeny detected variations in the ratio of 2 ' 8 ~ and o 2 ' 4 ~ 0Also, at this location was larger than at the above ground location and much more variable in time. This sensitivity of the Sabre-system leads to a much more precise measurement of the actual exposure of the workers in real time. Figure 2. Variation of the concentration of radon progeny over a period of one year at an underground location in Sudbur ON, Canada. The upper distribution is from 2 ' 4 ~ o and the lower distribution is from /Â'PO. Notice that the scaling factor is different for the two isotopes. Copyright 0 2007 by the American Association of Radon Scientists and Technologists, Inc. www.aarst.org 25 Proceedings of the 2006 International Radon Symposium September 17 - 20,2006 The time variation of the relative ratio of the two progeny in Figure 2, demonstrates the effect of the changes in the concentration of the ambient trace gases at the detector location. The calibration is determined dynamically from the continuous monitoring of ambient air at this location in order to account for these variations in the concentration of the individual progeny. The above two examples demonstrate the need for dynamic surveillance to define restricted "airborne radioactive areas" as required by the regulatory agencies. In essence, the regulations require that more frequent monitoring is done under changing operating conditions. Continuous monitoring with energy sensitive spectrometry fulfills this need as shown above with high sensitivity. DISCUSSION The Sabre-system is a WEB-enabled Internet based system capable of operating unattended for prolonged periods of time. The time variation of the raw data obtained from the radon monitor may be presented as equilibrium equivalent radon concentration or as working level values depending on the relevant calibration factors as needed. The calibration factors are determined dynamically as a function of time from the relative ratio of the ^PO and ^PO. Calibration of the radon measurements with the Sabre-system was based on a n in air at I m ~ ~ level / m ~ methodology developed by Kiko [12] for 2 2 2 ~measurements and above. This methodology allowed for the dynamic self-calibration of the Sabresystem under varying ambient conditions in air at any given location. The dynamic selfcalibration capability allowed for the reporting of radon concentration values in ambient air without assuming an arbitrary equilibrium ratio for the radon progeny at a measured location. The Working Level (WL) values were measured with high sensitivity in realtime because of the large volume of air continuously sampled with the Sabre-system. The self-calibration capability and the high sensitivity of the Sabre-system make it a unique radon monitoring system for demonstrating compliance with regulations in real-time. The data in Figure 1 show the variation of the concentration of radon over a 3 y period at an above ground location in Sudbury, ON, Canada. The observed seasonal variations at this location with maximum radon levels occurring in the spring indicate a range of radon concentration values from 0.2 pCi/L to 2 pCi/L. The variation of the two polonium progeny tracked each other indicating that the relative ratio of the unattached fractions of the radon progeny at the detector location was quite stable over the measurement period. Working level values indicated that this location was compliant with the regulatory guideline for monitoring in the lowest range of permissible exposure < 0.06 WL for Ontario. The data in Figure 2 demonstrate the need for continuous monitoring in the assessment of the actual exposure received both at the above ground and underground locations. When the operating conditions were changed in the ventilation provided at this location, the Copyright 0 2007 by the American Association of Radon Scientists and Technologists, Inc. www.aarst .orq 26 Proceedings of the 2006 International Radon Symposium September 17 - 20,2006 radon concentration levels and the working level values measured at this location fell into different regulatory requirements for monitoring radon at different times during the monitoring period. The required monitoring schedules were more frequent than the low radon environment above ground as per regulations. This is a demonstration of the continuous radon monitoring in real-time for the characterization of the ambient radon levels as discussed below, and for assessing the actual exposures received by the workers. Compliance with the ICRP recommendations on the exposure requires in Ontario, Canada, that a different schedule for monitoring is required at different ranges of WL values as quoted below: "(3) The air to which workers may be exposed in an underground mine shall be retested, (a) at least monthly, if the concentration of radon daughters in a sample exceeds 0.1 WL; and (b) at least quarterly, if the concentration of radon daughters in a sample is greater than 0.06 WL up to and including 0.1 WL. (4) If the concentration of radon daughters in a sample is less than or equal to 0.06 WL, a competent person shall assess once a year whether to retest the air in the work area in the underground mine and in making the assessment shall consider previous test results and changes in the mine or its operations." [I 31 Because of the high cost of providing the ventilation in underground locations, ventilation may be cut back for operational reasons. At such times, the ambient concentration of radon seems to go above the recommended action level for significant periods of time. Therefore, the minimum that is required to be done under the ICRP guidelines is to characterize the radon levels and their progeny concentrations simultaneously in order to identify what the actual WL values are, on an ongoing basis. This can be done with a continuous radon monitor such as the Sabre-system demonstrated in the present work. CONCLUSIONS The data presented above demonstrate the versatility and utility of the Web-based Sabresystem for the continuous monitoring of radon in the workplace and elsewhere with high sensitivity. Sabre-system fills the need for the characterization and identification of compliance with the ICRP recommendations for the radiation protection in a workplace and of the public in real-time. The capabilities of the system presented in this work, and the results presented above demonstrate the need for continuous monitoring for the characterization of the workplace. The added capability of energy spectrometry demonstrates that the actual exposures can be determined with greater precision with real-time measurements as identified by EPA. The results obtained in the present work could stimulate discussion about radon Copyright 0 2007 by the American Association of Radon Scientists and Technologists, Inc. www.aarsl.org 27 Proceedings of the 2006 International Radon Symposium September 17 - 20,2006 monitoring compliance in the mining industry and other high occupancy underground sites for the enforcement of OSHA and NRC regulations in real-time. In their debate five years ago, Thomas and Lindell [14] pointed out that the protection quantities in radiological protection should be expressed in terms of measurable physical quantities. The present work demonstrates that this ideal can be achieved in real-time beyond the compliance requirements, with well-designed continuous radon monitors and working level devices. Determination of the required parameters in a cost effective manner on an ongoing basis will be pursued as part of the next phase of these investigations. ACKNOWLEDGEMENTS This work is supported in part by the N O W Group OrganizationyCambridgeyMAyU. S. A. and Guelph, ONy Canada. The encouragement and guidance given by Mr, Geoff Byford of the Office of Research, University of Guelph is gratefully acknowledged. Biological Effects of Ionizing Radiation BEIR VI Report: The Health Effects of Exposure to Indoor Radon, National Academy Press 1999. International Commission on Radiological ProtectionyRadiation Protection of Workers in Mines. ICRP Publication 47. Pergamon Press, Oxford and New York (I 986). NRC Regulations 1OCFR Part 20 - Standards for protection against radiation: 1OCFWO. h~p:llwww.nrc,gov/~ading-rmldoc-collections/cfrlpa~O2Ol OSHA 29 CFR 1910.1096, Ionizing Radiation published 06/27/74yFederal Register, vo139, ~23502,amended 101241197gYFR vol. 43Âp 49746; 1 1/7/1978 FR vol. 43, p 51759,413011984, FR vole49, p 18295, FR ~0158,no 124, p 35309, 612011996 FR ~01.61 no. 46, p 3 1427. h~p:l/www.osha.gov/pls/oshaweb/owadisp,show~document?p~table=~TEW~TATIONS&p~id =24496 D0E:PNNL- I4 lO8:Occupational exposure to radon and thorony Strom, D. JSyReify R. H. et a!, Department of Energy, USA, 1996. h~p:llwww.pnl.gov~ayesian/strodpdfslS~om 1 996A-PNNL1.pdf 141O8~Occ~Exp~to~Radon~Thoron~DOE-RCCC-1996-0 Radon toxicity standards and regulationsyDepartment of health and human servicesyAgency for toxic substances and disease registry, h~p:llww.atsdr.cdc.gov~EClCSEM/radonls~ndards~regulations.html ICRP Publication 35. General Principles of Monitoring for Radiation Protection of Workers. Annals of the ICRP 9, N0.4ÂPergamon Press (1 982). ICRP Publication 37, Cost-benejit Analysis in the Optimization of Radiation Protection. Annals of the ICRP loyN0.213~Pergamon Press (1983). Copyright 2007 by the American Association of Radon Scientists and Technologists, Inc. www.aarst.orq 28 Proceedings of the 2006 International Radon Symposium September I 7 - 20,2006 9. http:llww.nrc.govlreading-mldoc-collectionslcfrlpa~O2Olappb/Radon-222.html 10. Wang, J.-X., Andersen, T., and Simpson, J. J., An Electrostatic Radon Detector Designedfor Water Radioactivity Measurements, Nucl. Instr. Meth A 42 I :60 1 609 (I 999). I I . Jagam, P., and Simpson, J.J., A High Sensitivity Monitor for Real Time Measurement of Radon and Thoron and Working Level Values in Air, Canadian Radiation Protection Association Bulletin, 23: N0.2: 9-1 I (2002)12. Kiko, J., Detector for 2 2 2 ~measurements n in air at the l m ~ ~ level, / m Nucl. ~ Instr. Meth A 460: 272-277 (200 I). 13. Ontario Ministry of Labor, Occupational Health and Safety Act, R.R.0, 1990, Regulation 854, Amended to 0. Reg. 630105, Mines and Mining Plants, Part XI, Working Environment, Sections 287-293. http:l/ww.e-laws.gov.on.c~BLawslRegs/English/9OO854~e.htm#BKl I 14. Thomas, R.H., and Lindell, B.In Radiological Protection, the Protection Quantities Should be Expressed in Terms ofhleasurable Physical Quantities, Rad. Prot. Dosim. 94, 287-292 (2001). - Copyright 0 2007 by the American Association of Radon Scientists and Technologists, Inc. wv\v.:iarst.orq 29