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.
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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.
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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
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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.
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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.
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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.
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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.

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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,
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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,
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Protection. Annals of the ICRP loyN0.213~Pergamon Press (1983).
Copyright

2007 by the American Association of Radon Scientists and Technologists, Inc.
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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
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Measurement of Radon and Thoron and Working Level Values in Air, Canadian
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n
in air at the l m ~ ~ level,
/ m Nucl.
~
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Meth A 460: 272-277 (200 I).
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Regulation 854, Amended to 0. Reg. 630105, Mines and Mining Plants, Part XI,
Working Environment, Sections 287-293.
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Rad. Prot. Dosim. 94, 287-292 (2001).

-

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