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Annals of the ICRP
Published on behalf of the lnternational Commission
on Radiological Protection
Editor:
M. C. THORNE,
ICRP, Sutton, Surrey
This report was adopted by the
International Commission on Radiological Protection 1981-f985
Chairman: Professor Bo Lindell, Statens strdlskyddsinstitut,
Vice-Chairman:
Dr. D. J.
Box,
60 204, 104 01 Stockholm, Sweden
Beninson, Comisiin Nacional de Energia At6mica, Auenida Libertador 8250,
1429 Buenos Aires, Argentina
Scientific Secretary: Dr. F. D. Sowby, ICRP, Clifton Aaenue, Sutton, Surrey SM2 SpU, England
Radiati
Members of the Main Commission of the ICRP
H. J. Dtnster, Chilton
W. Jacobi, Neuherberg
C. B. Meinhold, Upton
H. P. Jammet, Fontenay aux
Roses
H-H. Wu, Beijing
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E. E. Pochin, Chilton (Emeritus)
W. K. Sinclair, Bethesda
J. Linieckl Lodz
T. Maruyama, Mishima
S. Takahashi, Nagoya (Emeritus)Jft
S. Taylor, Bethesda (Emeritus)
L.
J. Vennart, Harwell
International Commission on Radiological Protection 1985-1989
Dr. D. J. Beninson, Comisihn Nacional de Energia At6mica, Aoenida Libertador
Chairman:
82s0,
1429 Buenos Aires, Argentina
Inte
Vice-Chairman: Dr. H. Jammet, Institut de Protection et de Sfireti Nucliaire, CEN FAR. B P. N"6, 92260 Fontenay
aux
Roses, France
Scientific Secretary: Dr.
M. C. Thorne, ICRP, Clifton
Auenue, Sutton, Surrey,
SM2 spu, England
Members of the Main Commission of the ICRP
R. J. Berry, London
C. B. Meinhold, Upton
H. J. Dunster, Chilton
A. K. Poznanski, Chicago
P. V. Ramzaev, Leningrad
W. Jacobi, Neuherberg
D. Li, Taiyuan
l.
E. Tajima, Tokyo
B. Lindell, Stockholm (Emeritus)
K. Z. Morgan, Atlanta (Emeritw)
E. E. Pochin, Chilton (Emeritus)
L. S. Taylor, Bethesda (Emeritus)
G. Silini, Vienna
W. K. Sinclair, Bethesda
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References
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SINflINOJ
PREFACE
In 1977, the Commission issued ICRP Publication 24, “Radiation Protection in Uranium and
Other Mines”. In 1982, ICRP Committee 4 on the Application of the Commission’s
Recommendations asked one of its members, R. Coulon, to prepare a revised version of the
report, to take account of important new information that had become available in ZCRP
Publication 32, “Limits for Inhalation of Radon Daughters by Workers”; the revised report was
also to be modified in the light of the Commission’s basic recommendations in ZCRP
Publication 26.
During the preparation of the report help was received from a number of colleagues, notably
A. Bouville, D. Cool, R. E. Cunningham and P. Zettwoog. The Commission wishes to express its
gratitude to all these individuals for their contributions.
The membership of Committee 4 at the time the report was adopted was:
H. Jammet (Chairman)
R. M. Alexakhin
R. Coulon
R. E. Cunningham
A. J. Gonzalez
0. Ilari
E. Kunz
J. Mehl
D. W. Moeller
R. V. Osborne
J. 0. Snihs
S. D. Soman
G. A. M. Webb
L. X. Wei
B. C. Winkler
Y. Yoshizawa
1. INTRODUCTION
1. The purpose of this report is to describe the principles and applications of methods by
which radiation hazards may be controlled in mines. Although primarily directed to the
uranium mining industry, the information presented in this report may be applied in varying
degree to all mines.
2. Miners are exposed to airborne radon, thoron, and their short-lived decay products, to ore
dust and, in some mines (particularly uranium and thorium mines) to external gamma and beta
radiations. In general, the short-lived radon decay products present the dominant radiation
risk. Radon is a member of the decay chain of uranium which makes up about 3 ppm of the
earth’s crust. Consequently, radon is not limited to mines; it occurs everywhere, outdoors in
usually low concentrations and indoors in higher concentrations. In underground mines, the
concentration of these radioactive contaminants, in the absence of adequate control measures,
can reach relatively high values.
_‘. Exposure of miners to high concentrations of radon and radon decay products has been
correlated with the induction of lung cancer in several mining groups. Miners’ deaths probably
attributable to the inhalation of radon and radon decay products are recorded as far back as the
sixteenth century.
4. The recognition of the role of radon and its decay products in the induction of lung cancer
in uranium miners led to exposure limitation guides. The establishment of a limit for the
inhalation of radon and its decay products has encountered substantial problems during the last
30 years. The Commission has recommended limits which have evolved during recent years
with the improvement of knowledge. For the purpose of radiation protection in mines, the
Commission recommended in ZCRP Publication 24, issued in 1977,’ a limit for the annual
average concentration of z22Rn, in equilibrium with its short-lived decay products.
5. In 1977, the Commission, in ZCRP Publication 26,2 introduced a new system of dose
limitation; more recently, in ZCRP Publication 303 the Commission proposed secondary limits,
expressed in terms of Annual Limits on Intake, derived on the basis of the most recent metabolic
and dosimetric data. Regarding the special case of occupational exposure to 222Rn, 220Rn, and
their decay products, the Commission recommended new limits for inhalation of radon decay
products by workers in ZCRP Publication 32.4
6. Exposures of personnel in underground mines are maintained within the recommended
limits primarily by mechanical ventilation in combination with other protective techniques. The
effort required to maintain satisfactory control is quite variable, depending on mining methods,
the geological formation, the concentrations of uranium and thorium in the rocks and minerals,
and climate.
7. The general principles of monitoring for radiation protection of workers have been
established by the Commission in ZCRP Publication 35.’ These principles provide the basis for
establishing monitoring programmes which contribute to meeting the objectives of the
Commission’s recommendations both effectively and economically. The main functions and the
various forms of monitoring are analysed with particular attention given to the design of a
monitoring programme and the interpretation of results for external radiation and for surface,
air, skin and internal contamination. The requirements for both ambient and personnel
monitoring in mines should conform with these general principles.
8. The scope of this report excludes the treatment of the other hazards, mechanical and toxic,
that are characteristic of all mining operations. However, the protective measures developed to
2
REPORT
OF COMMITTEE
4
control radiation exposures may influence the situation regarding other hazards. The high
ventilation rates usually needed to control the concentration of radon decay products are likely
to be more than sufficient for the dilution of toxic air contaminants, but will also tend to dry
surfaces in a normally wet mine, thereby enhancing the dispersion of dust, possibly containing
silica or other harmful agents in addition to radioactive nuclides, unless appropriate measures
are taken.
2. DESCRIPTION OF THE MINE ENVIRONMENT
9. The radiation environment in mines is complex and variable. Miners are exposed to
airborne radon, thoron, short-lived radon and thoron decay products, long-lived radionuclides
in ore dust, and to external gamma and beta radiation. All of these types of exposure warrant
consideration in formulating control procedures.
10. The noble gas “‘Rn produced by decay of 226Ra in ore bodies, migrates through rock
and emanates continuously from mine surfaces into all air spaces. After emanation, it is carried
along in ventilation currents and produces the solid decay products 218Po, 214Pb, 214Bi and
214Po (RaA, RaB, RaC and RaC’). The build-up in concentration of radon and its decay
products is particularly complex because of the physical properties of the respective species.
Being a noble gas, radon itself remains in mine air until the air is discharged above ground.
Because of its relatively long half-life (3.82 days) compared with the residence time of air in a
mine, radon concentrations increase in proportion to its rate of emanation and to its travel time
along different mine passages. By contrast, “*PO has a half-life of only 3.05 min and thus builds
up rapidly with time, giving rise to its immediate decay products, all of which have fairly short
lives (214Pb, 26.8 min; 214Bi, 19.9 min; 214Po, 2.74 x lob6 min). After formation, “*PO exists
briefly in atomic form, before becoming attached to aerosol particles or solid surfaces. In aerosol
form, the radon decay products tend to remain suspended, although they are subject to
electrostatic, inertial and diffusive forces by which they can be removed from mine air. In any
case, activity concentrations of these radon decay products increase rapidly with increasing
residence time of the air in the mine. The factors which contribute further to the variability in
concentration of these radionuclides are changes in radon emanation rate into mine spaces
brought about by alterations in the differential air pressure (both naturally and mechanically
induced), changes in ventilation rate and variations in mining activity. Consequently, the
relative composition and concentration of the mixture of radon decay products at any given
location can only be determined by measurement. Even in a mine under adequate control, the
concentration of radon decay products may vary considerably within the mine, from that of
ambient air at the point where fresh air is drawn into the mine, to high levels in exhaust air. This
must be taken into account in monitoring and control.
11. It is recognized that ‘*‘Rn exhalation from rock is also a source of radiation exposure;
220Rn (also called thoron) is a decay product of 232Th. The physical properties of 220Rn and its
decay products, and consequently their behaviour in mines, are almost the same as those of
222Rn and its decay products. However, when the masses of uranium and thorium per unit mass
of rock are similar, the relative importance of “ORn is expected to be less than that of 222Rn,
since its half-life is only of the order of one minute, and also because the specific activity of 232Th
in ore bodies is less than that of 238U . However, in some mines, high concentrations of thorium
are present and, in these circumstances, exposure to “‘Rn and its decay products may be
predominant.
12. Ore dust, containing members of the uranium and thorium decay series, is dispersed
RADIATION
PROTECTION
OF WORKERS
3
IN MINES
directly from mining operations and may be resuspended from surfaces by rapid air currents or
mechanical disturbances. Concentrations are quite variable with time, location and moisture of
the ore, ranging from essentially zero in quiescent conditions to extremely high values near
blasting.
13. Gamma radiation is emitted from radionuclides in the mine rock and results in external
irradiation of workers within the mine. The most important contributors to the gamma dose
rate are two short-lived decay products of “‘Rn retained in the rock, namely 214Bi and 214Pb.
The dose rate varies with location in a mine, depending on the radium content of the
surrounding rock and its presence in minerals. In shafts and tunnels through barren rock in
uranium mines, the absorbed dose rate is low, generally < 1 pGy h-‘. In workings, dose rates
are higher, typically 5-15 pGy h-‘, depending on the geometry, for ores of 0.2% U,O, or
equivalent by mass. In richer ores, the values are correspondingly larger. Dose rates of the order
of 1 mGy h- ’ have been observed, corresponding to exceptional ore lenses of about 2&30%
U,O, or equivalent. A rule of thumb is that d= 50 C where b is the absorbed dose rate in air,
expressed in pGy h - ‘, and C is the ore content, expressed in % U,O, or equivalent. Beta
radiation is of less importance. The ratio of the absorbed doses in air from beta and gamma
radiation is typically 0.5 near, and 0.2 at one meter from, the surfaces of uranium-bearing
material.
14. In a comparison between uranium or thorium mines and non-uranium mines (such as
coal or metalliferous mines), the situation is not found to be fundamentally different, except that
exposure due to external irradiation and inhalation of ore dust, containing radionuclides of the
uranium and thorium decay series, is generally small in non-uranium mines. The main problem
is the inhalation of 222Rn and of its decay products as well as, but to a lesser extent, the
inhalation of “‘Rn and its decay products. As in uranium mines, 222Rn is mainly transported
from the surrounding rocks to the galleries through water or air circulation. The importance of
each transfer process depends on the geological and tectonic fractures of the formation and of
the hydrologic behaviour of the aquifer during the mining operations. Measurements have been
made in several countries and are reported in various publications.6-8
15. Although the individual doses may be similar in non-uranium mines to those in uranium
and thorium mines, the collective dose in mining occupations other than uranium mining is
likely to be greater because of the larger number of people employed. Radiation protection in
non-uranium mines should be given more consideration than it has received in the past.
3. GENERAL PRINCIPLES FOR THE LIMITATION
OF EXPOSURE
16. The system of dose limitation recommended by the International Commission on
Radiological Protection is given in ICRP Publication 26,2 and is based on three principles:
-no practice shall be adopted unless its introduction produces a positive net benefit;
-all exposure shall be kept as low as reasonably achievable, economic and social factors
being taken into account; and
-the dose equivalent to individuals shall not exceed the limits recommended for the
appropriate circumstances by the Commission.
17. These three components are usually identified by the abbreviated terms “justification of
the practice”, “optimization of radiation protection” and “application of dose limits”.
18. The [email protected] of a practice that results in radiation exposure must take into account all
of the considerations, including social, economic and radiological impacts, necessary to
4
REPORT
OF COMMITTEE
4
determine if a positive net benefit is obtained. The requirement of justification does not apply
independently to ore exploitation because this activity is simply one part of a practice (e.g. the
coal or uranium cycle for energy production) which should be justified as a whole.
19. The optimization of radiation protection consists of selecting a level of protection such
that the efforts required to achieve further reductions in the radiation detriment are greater than
the resulting improvement. The use of this principle implies, taking into account operational
and other constraints and changing conditions, a comparison between the costs due to the
implementation of the various measures of protection that can be envisaged (for example those
aiming at the reduction of radon exhalation and at its extraction from exploited areas) and the
resulting reduction in terms of individual and collective dose equivalents.
20. The Commission, in ICRP Publication 26, proposed differential cost-benefit analysis as
one method for implementing the optimization principle. This procedure assists in the selection
of a protection level by comparing the marginal cost necessary to obtain an increased level of
protection with the marginal cost assigned to the detriment saved. These concepts have been
defined clearly in ICRP Publication 37,’ which also includes a number of application examples,
one of which is relevant to uranium mines. In ICRP Publication 37, it was also noted that
techniques other than cost-benefit analysis, such as multicriteria methods, may be used in the
optimization of radiation protection; these permit the inclusion of factors other than collective
dose, for instance the distribution of individual doses.
21. The dose limits act as a constraint in the procedure of optimization and constitute a
guarantee of sufficient protection for each individual. The dose-equivalent limit recommended
by the Commission applies to the sum of the dose equivalent resulting from external irradiation
during a year and the committed effective dose equivalent resulting from any intake of
radionuclides during the same year. The dose from radon decay products is virtually all
delivered within a few hours of intake.
4. LIMITS FOR INDIVIDUAL EXPOSURES
22. The System of Dose Limitation requires that the annual doses incurred by occupationally-exposed persons do not exceed the dose limits recommended for the appropriate
circumstances by the Commission. For stochastic effects, the Commission recommends that the
sum of the dose equivalent from external irradiation and the committed effective dose
equivalent from internal irradiation be limited to 50 mSv in any year. For non-stochastic effects,
the corresponding annual limit is 500 mSv for any organ or tissue, except the lens of the eye for
which the limit is 150 mSv.
23. The summation of external and internal contributions will often be necessary in mines
because miners may be exposed simultaneously to a number of different sources, including
external gamma radiation; radon, thoron and their decay products; and ore dusts containing
uranium, thorium and their radioactive decay products. In the following sections of this chapter,
each of these sources of exposure, together with their respective limits, are discussed separately
so that the unique terms and units used in describing each source may be clearly defined. Overall
compliance with the recommended individual limits is determined by summing the various
sources of exposure, and is treated in paragraphs 4143.
4.1. External Exposure
24. In principle, external exposure to both beta and gamma irradiation has to be considered
for individuals present in uranium and thorium mines. Because of the wide distribution of the
RADIATION
PROTECTION
OF WORKERS
IN MINES
5
radiation sources in such mines and the high gamma energies associated with the uranium and
thorium decay series, external gamma irradiation can be considered to result in essentially
uniform whole-body exposure. Because beta doses to the skin are generally much lower than
whole-body doses from gamma irradiation and because the limit on effective dose equivalent is
a factor of ten lower than the limit on dose equivalent in the skin, it is not generally necessary to
take into account skin doses due to beta irradiation.
4.2. Internal Exposure
Decay products of 222Rn and 220Rn
25. In recent years, substantial epidemiological and dosimetric information has been
collected, upon which the exposure limits to radon decay products can be based. These data, and
the recommended limits for inhalation of radon decay products by workers, are presented in
ZCRP Publication 32.4 The Annual Limit on Intake, ALI,, for the potential alpha energy of any
mixture of short-lived radon decay products, is the quantity for which the Commission has
recommended a primary limit. As indicated in ICRP Publication 32, for decay products of 222Rn
the ALI, is 0.02 joule. The corresponding value for decay products of 220Rn is 0.06 joule.
26. Derived quantities, such as the Annual Limit on potential alpha energy Exposure (ALE,)
and the Derived Air Concentration (DAC) may be obtained from the ALI, in the practical units
used by the mining industry. Numerical values are summarized in Table 1, based on
information presented in ICRP Publication 32.4
27. Since the limits given in Table 1 all relate to a Committed Effective Dose Equivalent
(CEDE) of 0.05 Sv, the corresponding dosimetric conversion coefficients are as listed in Table 2.
The dosimetric conversion coefficients have been reviewed in an OECD/NEA report, lo which
includes consideration of the physical characteristics of 222Rn and 220Rn decay-product
aerosols under different environmental conditions in mines.
Table 1. Recommended
Annual
Limits on Intake (ALI) and exposure (ALE) and Derived
(DAC) for ‘**Rn and s2”Rn Decay Products”
Air Concentrations
Decay products
Type of limit
ALI,
Quantity
Unit
ALE,
Potential a energy
Equil.-equiv.
Rn activity’
Time integ. potential a energy concentration
DAC?
Time integ. equil.-equiv. Rn concentration
Potential a energy concentration
J
Bq
Jhme3
or
WLMd
Bqhme3
Jme3
Equil.-equiv.
:L’
Bq mm3
Rn concentration
Notes.
a Primary limits are underlined. For practical application,
b Based on a mean breathing rate of 1.2 m3 h-i during
’ See paragraph
28.
d Working Level Month.
’ Working Level.
f *‘sPo (RaA) to ‘14Po (RAC’).
8 “‘Pb (ThB) to =‘Po (The’).
Z22RnT
=0Rn8
0.02
3.6 10
0.017
0.06
8.0 lo*
0.050
4.8
3.0 lo6
8.3 1O-6
14
6.6 105
2.5 10-s
0.4
1500
1.2
330
the derived values can be rounded to one significant
a,working period of 2 000 h per year.
figure.
REPORT OF COMMITTEE 4
Table 2. Committed effective dose equivalents corresponding to unit values of various quantities relating
to levels of radon and thoron decay products in air
Dosimetric Conversion Coefficient
Quantity
Equil.-equiv.
Rn-activity
Time-integrated
equil.-equiv.
Rn-cont.
Equil.-equiv.
Rn-cont.
“‘Rn
r2*Rn decay products
220Rn decay products
1.4 lo-sSv/Bq
6.2 10-s sv/Bq
1.7 10-s Sv/(Bq h rne3)
or
1.0 1O-2 Sv/WLM
3.5 10-s (Sv y-r)/(Bq me3)
7.6 10-s Sv/(Bq h rns3)
or
3.5 1O-3 Sv/WLM
1.5 10e4 (Sv y-t)/(Bq m-s)
and “‘Rn
28. As discussed in the previous section, the Commission recommends that the primary
control quantity in mines should be the potential alpha energy intake. However, some national
authorities may wish to use the measurement of radon concentrations to exercise control of
radon decay product concentrations, since it is an easier quantity to measure than the potential
alpha energy. The relationship between the equilibrium equivalent 222Rn concentrations,
given in Table 1 and the activity concentration, C,,, for 222Rn itself in air is given by:
EC2224
G,
=EC222JF
For any given co-existing concentration of radon and short-lived decay products in the
atmosphere, F is the ratio of the total potential alpha energy of the actual decay product
concentrations to the total potential alpha energy that the decay products would have if they
were in equilibrium with the radon, The limits given in Table 1 may, therefore, be expressed in
terms of the 222Rn activity concentration by division of the appropriate value (ALE or DAC) by
the equilibrium factor F.
29. The use of 222Rn activity concentration limits for assessing the significance of radon
measurements requires that the value of the equilibrium factor F be available. If measured
values for Fare not available, an applicable value can still be determined for some situations
from information relating to the ventilation rates and aerosol conditions in the mines. In
ventilated mines, where the ventilation conditions are normal, the value of F can usually be
taken as 0.5. However, national authorities should establish the values of F to be used in the
operations for which actual measurements of the equilibrium factor are not required. Further
considerations are given in Appendix C of ICRP Publication 37.
30. In some special circumstances, the value of Fmay be very low, so that exposure to radon
gas becomes relatively important: this is the case, for instance, when air filtration or electrostatic
precipitation of radon decay products is performed, and also when respirators are used.
31. The Commission’s recommendations related to exposure to radon gas were given in
ZCRP Publication 32, and are summarized in Table 3. The DAC for 222Rn decay products and
the DAC for 220Rn decay products being respectively l/100 and l/500 of the DAC for 222Rn and
the DAC for 220Rn, the contribution of “‘Rn gas and 220Rn gas can be neglected in most
conditions.
32. The dosimetric conversion coefficients that can be derived from these limits are given in
Table 4.
RADIATION
PROTECTION
OF WORKERS
IN MINES
7
Table 3. Recommended Annual Limits on Exposure (ALE) and Intake (ALI)
and Derived Air Concentrations (DAC) for “*Rn and ‘a”Rn in the absence
of decay products. The primary limits are underlined. For practical
application, the derived values can be rounded to one significant figure
Type of limit
ALE
ALI
DAC
Unit
222Rn
Bq h m-3
Bq
Bq m-3
3
3.6 10”
1.5 105
5
6.0 lo*
2.5 lo5
a Assuming a mean breathing rate of 1.2 m3 h- ’ during a working period of
2 000 h per year.
Table 4. Committed effective dose equivalents corresponding to unit values of various quantities
relating to levels of 222Rn and ‘*‘Rn in air
Dosimetric conversion coefficient
Quantity
Activity
Time integ.
activity cont.
Activity cont.
1.5 10-r’ Sv/Bq
0.9 lo- lo Sv/Bq
1.8 10-r’ Sv/(Bq h md3)
3.3 lo-’ (Sv y-r)/(Bq rne3)
1.1 10-r’ Sv/(Bq h rnm3)
2.0 lo-’ (Sv y-r)/(Bq rnm3)
Ore dust
33. Although, in the case of ore dust, inhalation is generally the most important route of
exposure, ingestion should not be ignored without some consideration of its potential
importance.
34. Following the methodology presented in ICRP Publication 30,3 the Annual Limit on
Intake for a mixture of long-lived alpha-emitting nuclides, ALI,, is defined as the largest value
of I which satisfies both of the following inequalities:
Ix&
(Hi per unit intake)l0.5
j
Zxf,
(Hi,,,
Sv for all T
per unit intake) SO.05 Sv
where: I(Bq) is the intake of the mixture, expressed as the total activity of long-lived a-emitters,
fj
the ratio of the activity of radionuclide j in the mixture to the total activity of
long-lived a-emitters,
is
Hi per unit intake (Sv Bq- ‘) is the committed
dose equivalent in organ or tissue T
resulting from an intake of unit activity of radionuclide j, and
HEj,5o per unit intake (Sv Bq-‘) is the committed effective dose equivalent correspond-
ing to an intake of unit activity of radionuclide j.
The first inequality relates to the limitation of non-stochastic effects and the second to stochastic
effects.
35. In the absence of information on the physical and chemical characteristics of ore dust in
mines, it may be assumed that all of the radionuclides in the 238U decay series are in secular
equilibrium, that the Activity Median Aerodynamic Diameter (AMAD) of ore dust is 1 pm and
8
REPORT
OF COMMITTEE
4
Table 5. Values used for the calculation of the Annual Limits on Intake for inhalation of long-iived nuclides of the
zOsU and r3rTh series
Radionuclide
238Uranium series
238U
2341J
230,
2z6Ra
“‘Pb
2’0Po
Inhalation
class
Y
Y
Y
W
D
W
ALI,
232 Thorium series
“‘Th
““Th
““Ra
ALI,
Y
Y
W
H E,5,, per unit intake
HT per unit intake
(Sv Bq - ‘)
(Sv Bq- ‘)
3.2
3.6
7.0
2.1
3.4
2.1
1O-5
10-s
10-S
10-s
1o-6
1o-6
8.7 1O-4
7.6 1o-6
5.5 10-s
-
1700Bq
2700Bq
3.1 lo-‘+
8.3 1O-5
7.9 lo-’
5.0 10-s
-
380 Bq
300 Bq
/
0.2
0.2
0.2
0.2
0.2
0.33
0.33
0.33
that the chemical form of the radionuclides corresponds to the most non-transportable form
considered in ZCRP Publication 30. Table 5 presents the values used for the calculation of ALI,
extracted from ZCRP Publication 30. Only alpha emitters were taken into consideration, since
the contribution of beta emitters is negligible. However, ” ‘Pb, which is a beta emitter, has been
included, since its decay in the body leads to alpha irradiation from *l”Po. With regard to
non-stochastic effects, the data presented in Table 5 refer to bone surfaces as tissue T, since bone
surfaces accumulate the highest tissue doses on the basis of the assumptions given above.
36. The Annual Limit on Intake corresponding to the inhalation of long-lived alpha emitters
of the 232Th series contained in ore dust is calculated under the assumption that 232Th, **‘Th
and 224Ra are in secular equilibrium and in the most non-transportable form considered in
ZCRP Publication 30.
37. The resulting Annual Limits on Intake for alpha activity of long-lived radionuclides
of
the 238U series and the 232Th series are given in Table 5. The AL1 for the 238U series is 1.7 kBq,
based upon the limitation of stochastic effects. The AL1 for the 232Th series is 0.3 kBq, and is
based upon the limitation of non-stochastic effects.
38. It may be the case that not all a-activity associated with the ore particles is due to the
long-lived a-emitters listed in Table 5. In particular, ***Rn- and **‘Rn-decay products may be
present in, or on, the particles. Because these are of relatively low toxicity, the committed dose
per unit of total particle-associated a-activity will be reduced, and higher derived limits will be
applicable in monitoring. Alternatively, an appropriate delay time between sampling and
measurement can be introduced, so that the a-activity assayed is that associated with the longlived a-emitters listed in Table 5.
From calculations taking into account the possibility of short-lived a-activity being
associated with ore particles, and also including various other factors, l1 it appears that ALIs for
ore dusts, defined on the basis of total a-activity and corresponding to the stochastic limit, could
range from about 1 kBq to 10 kBq for the inhalation of uranium ore dust and from about
0.3 kBq to 5 kBq for the inhalation of thorium ore dust. The parameter with the most
substantial effect on the ALIs is the particle size distribution: the lowest and highest values of the
RADIATION
PROTECTION
OF WORKERS
9
IN MINES
ranges are obtained for particle sizes of0.5 and 10 nrn respectively. Calculations for particle sizes
greater than 10 pm may result in even higher values.
4.3. Derived Limits and Reference Levels
39. Many of the measurements made in the course of a monitoring programme cannot be
expressed directly in terms of the quantitative recommendations of the Commission. Derived
limits are generally introduced to provide a quantitative link between the quantity being
measured in the monitoring programme and the dose equivalent limits, or annual limits on
intake, recommended by the Commission. In mines, derived limits may refer to the gamma dose
rate, the concentrations of 222Rn, 220Rn and of their decay products, or the concentrations of
natural radionuclides in ore dust.
40. It may also be desirable to set reference levels for each exposure pathway. A reference
level is the pre-determined value for any of the quantities that may be encountered in the
monitoring programme which, if exceeded, will require particular action, such as investigation
or corrective measures. This concept is defined in ZCRP Publication 26, and its use for the
purpose of monitoring is discussed in ZCRP Publication 35. Exceeding an investigation level
may, in some cases, determine an enquiry into the causes of this event. These levels, and the
conditions of their application, are dependent on the mining conditions, and must take into
account changes in these conditions.
4.4. Combination of Limits
41. As indicated in the introduction to this chapter, the Commission’s recommended
individual dose limits are intended to apply to the sum of both external and internal dose
contributions. This condition will be fulfilled if the relationship:
is satisfied, where HE is the annual effective dose equivalent from external radiation, HE,L is the
annual limit on the effective dose equivalent, 4 is the annual intake of the group of nuclidesj, and
ALIj is the annual limit on intake for the group of nuclides j.
42. The requirement for additivity has the effect of reducing the allowable inhalation of
222Rn decay products below their recommended limit by an amount dependent upon the
concurrent exposure to external radiation, 220Rn decay products, and ore dust. For the
limitation of stochastic effects, the combination formula can be expressed as:
H
-_-E”“‘+++ITn+++IThg
a
C
e
where: H E.ext is the annual effective dose equivalent from external radiation,
4, is the annual intake of potential a-activity from 222Rn decay products,
4, is the annual intake of potential a-activity from 220Rn decay products,
(, is the annual intake of a-activity associated with uranium ore dust, and
&,, is the annual intake of a-activity associated with thorium ore dust.
a, b, c, d and e are the corresponding
d= 1700 Bq and e=380 Bq.
annual limits: i.e. a=0.05
Sv, b=0.02
J, c=O.O6 J,
10
REPORT
OF COMMITTEE
4
43. In practice, since intakes of thorium ore dust alone are limited by non-stochastic
considerations, and because such dust invariably constitutes only a small component of total
exposure, compliance with the above formula will ensure that non-stochastic limits are
complied with.
4.5. Levels for Special Operational Decisions
44. In mines with potentially high radon and thoron concentrations, situations may arise
requiring special operational decisions. In order to maintain, in such situations, a good control
of exposures, the following reference levels may be used in practice:
(a) Access to mine areas that are not currently worked, in which the radon decay product
levels are unknown, should, as a rule, be controlled, unless there are reasons to believe
that the average equilibrium-equivalent
radon concentration
is less than about
1 kBq rnw3.
(b) The use of filtering respirators approved for protection against radon decay products
should be satisfactory in areas with ECZZZ~, up to about 10 kBq m-j, and the use of
approved supplied-air respirators should be satisfactory up to about 100 kBq rne3. In
areas with ECmR,, between about 10 kBq mm3 and 100 kBq me3 the use of filtering
respirators should be combined with a proportional reduction of the working-time.
(c) Parts of the mine with ECmRn expected to be higher than about 100 kBq me3 should be
marked with a sign indicating the radon hazard.
(d) The release of radon from radon-rich water in the mine may occasionally cause high
radon and radon decay product levels. Therefore, the air concentrations resulting from
the use of radon-rich water for drilling or for dust suppression should be measured,
particularly if the water radon concentration exceeds about 50 kBq rnm3.
5. CONTROL
OF RADIATION
EXPOSURE
45. There are two considerations that must always be kept in mind when establishing the
system for controlling radiation exposure. The first of these is the optimization of protection.
The optimization requirement will occur both before the opening of the mine and during the
operation of the mine. In the first case, optimization will influence the design of the mine, and
possibly even the type of operation to be used. Once operations are in effect, however,
optimization is still required to maintain exposures as low as reasonably achievable. The second
consideration is that the individual dose limits, as expressed in ZCRP Publication 26 and detailed
in Chapter 4, must be met for all workers.
46. The principal techniques for controlling exposures in mines are control of the source,
mechanical ventilation, isolation, and air cleaning. Operational activities, such as organization
of work and backfitting, may also be useful, as well as, in certain situations, personal protection
equipment. These techniques are used in both the limitation of individual doses and the
optimization of the level of radiation protection, but are applied somewhat differently. When
determining compliance with the individual dose limits, measurements and models should be
conservative in nature, and the choice of assumptions to be used must ensure that the risk of
RADIATION
PROTECTION
OF WORKERS IN M1NE.S
11
under-estimating the exposure of an individual is acceptably small. However, modelling of the
impact of actions taken to optimize radiation protection should be as realistic as possible, so
that no bias is introduced in the optimization process.
47. In open-pit mines, the relative contributions of external exposure, radon, thoron and
their decay products, and ore dust, may differ somewhat from that in underground mines.
However, the same type of considerations will be required because the same types of hazards are
present. In non-uranium mines, the contribution from ore dust and external exposure will
generally be low. In these cases, the only important factors may be radon and radon decay
products.
5.1. Design of Protection
Choice of mining method
48. When evaluating the various methods of mining, radiation protection requirements
should be given careful consideration in the early stages of design. The choice of a particular
approach, such as open-pit or underground, and the proposed layout of the operation, will have
an influence upon future worker exposure which cannot be ignored. For instance, in the case of
ore bodies with a high uranium content (higher than 1% in underground mines), special mining
methods, such as remotely-operated tools, may have to be considered in order to maintain
external exposure within the limits. Likewise, the integral design of adequate ventilation might
alter the manner in which the mine is designed, or the equipment which is ordered (i.e. a
provision for ventilated cabs in open-pit mining equipment). When optimizing radiation
protection in mines, it must be remembered that the collective dose is related to the total number
of workers and to the total amount of ore extracted. However, it must also be realized that other
technical and economic criteria will generally weigh more heavily than the radiation protection
criteria in the selection of a mining method, although radiation protection criteria can play a
determining role when deciding between two otherwise comparable options.
Source isolation
49. Reducing radon emanation into the mine cavity represents an ideal method of control,
but present capabilities of implementation are limited. Despite considerable experimentation,
application of sealants to rock surfaces has not yet been found to be economically effective.
Nevertheless, all practical measures should be taken to reduce the quantity of radon entering
supply airways.
50. Abandoned workings constitute an increasing source of radon as mining progresses.
These areas are closed off to conserve ventilating air. In the absence of ventilation, radon
concentrations increase enormously behind the barrier. However, the activity released to
working areas of the mine is reduced because of the hold-up time provided by the barrier.
Barriers alone are not completely effective because pressure fluctuations within the mine cause
pressure differentials, which induce radon leakage through the barriers or through adjoining
rock. The effect can be counteracted by maintaining a slight negative pressure in the closed-off
area with respect to the active area. The exhaust air must be discharged above ground or
through a duct into spent ventilating air within the mine. The abandoned workings may be filled
with barren sand or waste rock which impedes diffusion of radon and reduces the amount of
exhaust air needed to maintain negative pressure. In this case, exhausting the air may obviate
the need for a seal, and a simple brattice may suffice. However, for non-uranium mines, waste
12
REPORT
OF COMMITTEE
4
rock itself might be a source of radon, and, because of the large surface-to-volume ratio of waste
rock, its use for this purpose needs to be carefully evaluated. In other respects, if closed-off
workings in uranium mines are reopened, *l”Pb may be a potential radiation hazard that needs
to be considered.
5 1. Water seeping from rock is another potent source of radon. Radon dissolves in water and
reaches equilibrium with the partial pressure of the gas phase in rock pores. Upon exposure to
the lower concentrations in mine air, the water releases most of the radon rapidly. Therefore,
water flowing from rock should be channelled into pipes and conducted away from occupied
areas before the radon is re-emanated.
52. Uranium ore itself is both the major source of external exposure and one of the more
obvious sources of radon. Since the fraction of radon that escapes from broken ore is directly
related to the exposed area, ore should not be cornminuted to sizes smaller than necessary for
efficient loading and hauling. Mined ore should not be stored near areas where active work is
occurring. This relatively simple consideration will reduce both external and internal exposure.
53. Investigations of rock sealants (mentioned above) and overpressure as methods of
reducing radon emanantion have yielded encouraging results, but both methods remain
essentially experimental. Several commercial sealing materials have been shown to be virtually
impermeable to gas diffusion but, for effective reduction of radon emanation, a rock sealant
must also adhere to the rock surface and must be readily applicable over extensive areas. None
of the tested materials to date is fully satisfactory in all three respects.
54. The generation of an overpressure within the mine diminishes the emanation of radon
from surfaces, but this effect is only transient unless a flow can be maintained through rock
interstices from the mine cavity. In shallow mines, especially in porous rock, convective flow
may occur to the surface. In deeper mines, abandoned workings or special vent holes may
constitute air sinks for interstitial air flow. In the present state of technology, the effectiveness of
this technique in specific mines must be determined empirically.
Mechanical ventilation
55. Mine ventilation must be designed to control, to an acceptable degree, the concentration
of radon and its decay products. In uranium mines, ventilation designed for the control of radon
decay products is usually adequate for other air contaminants as well, although it is always
prudent to confirm that the concentration of contaminants such as carbon monoxide, oxides of
nitrogen and silica are within the appropriate limits. The source of 222Rn is 226Ra distributed in
surrounding rock or radon-rich water. Emanation and exhalation of “‘Rn is continuous into
all mine spaces, the rate depending on the radium content of surrounding rock, the porosity and
degree of fracturing of the rock, and pressure gradients, both natural and artificial.
56. Once in the mine air, 222Rn remains entrained until the air is discharged above ground.
Its half-life is too long compared with its residence time in mine air at normal ventilation rates
for its concentration to diminish significantly by radioactive decay. Its control can, therefore, be
regarded as a conventional dilution problem. Although its emanation rate varies with location,
as a first approximation 222Rn concentration is proportional to the distance travelled by the air
through the mine and, consequently, to the transit time of ventilating air, assuming a constant
tunnel cross-section. Thus, the concentration increases continuously with time along airways,
regardless of mining operations.
57. Since immediate decay products of 222Rn have very short half-lives, the concentration of
their potential alpha energy increases with time and, at a constant radon concentration, is
approximately proportional to t O.“, where t is the number of minutes of growth, for t less than
40 min. Therefore, the potential alpha-energy concentration, arr,of air with a concentration, C, of
RADIATION
PROTECTION
OF WORKERS
IN MINES
13
222Rn at a time t min after it was completely cleared of radon decay products, can be estimated
by means of the following general equation:
t 0.85
E,=&;,C
-
0 t;
where t; is 1 min; and
E;, is the potential alpha-energy concentration per unit concentration of 222Rn after
1 min growth (as a simplification, it may be assumed that the equilibrium of radon and
its decay products will not change in the range of the ventilation flow rates usually
encountered in mines).
Therefore, time is a vital consideration in ventilation design. Details on radon ingrowth are
given in Appendix D of ICRP Publication 37.
58 The half-life of 220Rn is only 55.6 s and it decays via 216Po, with a half-life of 0.15 s, to
212Pb with a half-life of 10.64 h. Thus, levels of 212Pb will, in general, reflect concentrations of
220Rn’in air.
59. Most mines consist of complex networks of active workings connected by tunnels and
shafts that serve as haulageways and air conduits. Thus, the foregoing simplified theoretical
representations of the growth of radon and its decay products are useful for predictive purposes
only within discrete segments of the mine, although the general principle of minimizing lengths
and times of air transit remains valid.
60. Air is usually impelled through the mine complex by primary and secondary ventilation
systems. For instance, the primary system might consist of high-capacity fans at the surface that
pull or push air through vent holes or shafts and through main tunnels connecting with other
vent holes where the air is drawn in or discharged, respectively. The secondary system consists of
small auxiliary fans within the mine that deliver portions of air from primary airways, often by
means of flexible ducts, to active workings. Secondary systems are modified continually to
maintain proper air distribution as ore bodies are excavated and abandoned. Barriers (doors
and bulkheads) are used to channel air through designated tunnels and to avoid recirculation.
61. Mine layout, a fundamental determinant of ventilation efficiency, should be guided by
requirements for the orderly development of an effective ventilation system. An important
factor is the radon concentration of the air used for supplying the stopes and secondary
ventilation systems. When this air has already passed through a portion of the mine, radon and
radon decay products will be present. A portion of dose received by workers in these areas will
therefore be caused by radon and radon decay products from other areas of the mine. Efforts
should be made to ensure that air provided to work areas and secondary ventilation systems is
as clean as possible. A large volume of air in these systems is also important to reduce dust
concentrations resulting from drilling, blasting, crushing and transport operation. However,
physical arrangements and methods of ore recovery differ so widely between mines, because of
variations in depth, rock hardness, orientation of ore bodies, water, and other factors, that only
very general recommendations have universal application:
(4 Fresh ventilating air should be delivered to active workings as directly as possible
through shafts and tunnels. Generally,
(overpressure systems).
it is preferable
(b) Mechanical ventilation should be operated continuously.
to use forced ventilation
If ventilation is interrupted,
affected areas should not be re-entered until ventilation has reduced radon decay product
concentrations to the previous values.
14
REPORT
(c)
OF COMMITTEE
4
Air velocities should be maximal, compatible with comfort and safety.
(d) Parallel distribution of air to active workings is preferable to series distribution so as to
avoid cumulative air contamination and to minimize resistance to air flow. In practice,
distribution systems in large mines use both parallel and series arrangements.
(e) Haulageways and miscellaneous work stations preferably should be located on the inletair side of the ventilation systems.
(f) Auxiliary fans should be used to distribute adequate fresh air to active workings located
off main air courses. Where ducts are necessary to deliver air to the termini of dead-end
tunnels, the points of discharge should be placed within 10 m of the working face.
(g) Recirculation must be avoided by arrangements
of stoppings and auxiliary fans.
(h) The quantity of primary air available to auxiliary ventilation installations should be at
least 1.5 times the total auxiliary fan capacity.
62. It will be noted that these recommendations are mainly directed to the expeditious use of
air, which is necessary to minimize ingrowth of radon decay products: this distinguishes
effective ventilation in uranium and other mines from ventilation designed to apply to toxic air
contaminants. These factors indicate the procedures that will be useful in meeting the individual
dose limits.
63. Optimization of the ventilation system is best accomplished by the original design of the
mine, rather than by backfitting to improve present circumstances. However, for mines that are
already in operation, optimization can still be achieved through improvements in ventilation
rates and secondary air movements. ZCRP Publication 37 provides an example of optimization
of a ventilation system. Detailed mathematical treatment of air-flow exchange rates, and other
factors that must be considered in designing mine ventilation, may be found in engineering
manuals, ZCRP Publication 37 and documents of the IAEA on this subject.
Air cleaning
64. Air cleaning as a means of reconditioning ventilating air for further use underground is
another control technique that merits wider attention than it is receiving. Some effort has been
made to remove radon itself from mine air, but efficient removal on a large scale is extremely
difficult and not likely to be achieved in the near future. On the other hand, radon decay
products and ore dust are removable by most conventional air cleaning methods although
filtration and electrostatic precipitation are the most efficient because of the small particle sizes
involved. Both of these methods are being applied with good results in a few mines. Air cleaning
is being used to recondition both primary air streams and selected branches of secondary
systems. Its more general use will probably depend mainly on economic considerations, the
most suitable application being in deep mines where the relative cost of air cleaning could be
competitive with the cost of augmenting primary ventilation. The effectiveness of air cleaning in
a given situation depends on the concentration of radon and radon decay products, the
efficiency of air cleaning, and the time delay between cleaning and use of the reconditioned air.
Even if radon decay products are completely removed (100% efficiency), their concentration
will begin to increase immediately (see paragraph 57) and this effect may result in optimum
cleaning being achieved at efficiencies considerably lower than 100%.
65. Enhanced plate-out is an effect associated with any substantial reduction in the
concentration of mine dust, whether the result of deliberate air cleaning or for another cause. It
occurs because, at the lower particle concentrations, the uncombined radon decay products
RADIATION
PROTECTION
OF WORKERS
IN MINES
15
exist in larger fractions and have a greater chance of depositing on solid surfaces. Some
experiments have been performed to determine how the effect might be exploited as a
supplementary means of controlling radon decay product concentrations, but practical
methods have not been established. A point that should be considered in any eventual
application is the possibility that the relatively more hazardous nature of uncombined radon
decay products may decrease the effectiveness of the procedure.
5.2. Operational Protection
Backfitting
66. During the mine operation, improvements can be made and different options are
available for reducing individual and collective doses. Since conditions within the mine are
constantly changing because of exploitation of new areas, reduction or increase in ore grade
being mined, and termination of work in some areas, the measures taken to reduce exposures
should also be changing so that protection is kept optimized. In some cases, this may involve
addition of new ventilation equipment or capacity, changing airflow patterns, or changing
stockpile areas and crushing operation locations.
67. Management must also prevent and/or compensate for reduced efficiency of
ventilation systems that are already in place. In some cases, such as uranium mines with a high
grade of ore, a system for rapidly detecting degradation may be necessary. In other cases, routine
surveillance may be sufficient to detect any problem. In any event, management must be
committed to the continual maintenance of ventilation systems, and the constant evaluation of
actions to reduce exposure.
Personal
68.
protective
equipment
Normally, the mildly radioactive uranium ore dust is not a significant source of external
exposure. A possible exception is beta radiation exposure to the skin from sustained direct
contact with highly-contaminated clothing. An additional source of skin exposure is the
deposition of radon decay products on the skin. Mine personnel should be provided with work
clothes, lockers and shower facilities, in conformance with good hygienic practice. Work clothes
should only be worn in the mine and should be laundered frequently.
69. Filter respirators and supplied-air respirators are used for the protection of individual
miners where air concentrations exceed prescribed reference levels (see paragraph 44). Such
areas consist mainly of unventilated, abandoned workings and developmental sections to which
entries should be infrequent and brief. Filter respirators specifically approved for radon decay
products may be used at concentrations that do not exceed the prescribed operational level by
more than the protection factor (1 -efficiency)- ‘, afforded by the particular respirator.
However, for the special case where approved high-efficiency filter respirators are worn, it is
recommended that the radon decay product exposure be assumed to be 10% of what the
estimated exposure would be without respirator protection.
70. However, it must be noted that the efficiency of respirators, when they are used in actual
mine conditions, may be lower than the efficiency measured in laboratory conditions,
particularly as a result of leakage round the face piece. Also, the use of respirators should be
limited to special cases, owing to the fact that the associated discomfort is hardly compatible
with routine working conditions in mines.
71. Exposure to radon itself in these situations may not be trivial because very high
concentrations are quite possible. Self-contained breathing apparatus may be used if protection
against radon as well as its decay products is warranted. However, these devices are
16
REPORT
OF COMMITTEE
4
cumbersome and their air supplies are limited, thus severely restricting the kinds of activity that
may be conducted. Protection is afforded more conveniently by properly used respirators
equipped with charcoal canisters, which are smaller, lighter in weight, and longer lasting than
compressed-air tanks. It is emphasized that, in the working environment, it is difficult to
maintain a respirator efficiency sufficient to decrease the exposure by a factor of more than
about ten.
Organization of work
72. The organization of work within a mine can have a great influence on the individual and
collective doses received. Particular attention should be paid to separating the normal
movement of workers from the transport and stockpiling of mined ore. This separation will
reduce the external exposure received and will also reduce the inhalation potential of radon,
radon decay products and ore dust during times when miners are not actively engaged in
mining. The proper organization of work is not intended to mean that workers should be
rotated so as to keep each individual exposure below the dose limits. Job rotation, which may
result in increasing the collective dose, should be used only within the frame of optimization of
radiation protection and should not replace measures for reducing individual doses. However,
rotation between various locations without change of functions would not necessarily increase
collective dose.
6. MONITORING
73. The purposes and principles of monitoring for radiation protection of workers have been
given in ZCRP Publication 35.’ These concepts can be applied to operations in mines. However,
the monitoring programmes have to take into account the exposure conditions found in mines.
External exposure rates are substantially constant with time, and can be predicted, to some
extent, from the ore grade. Internal exposures, on the other hand, are variable and seldom
predictable over any length of time.
74. The environment in a mine can be described as corresponding to a variable, but
essentially continuous, contamination of the workplace as a result of normal operations. There
are two particular purposes for monitoring in this type of environment, and in mines in
particular, which must be kept in mind. The first is to manage and to keep account of individual
exposures to ensure that the dose limits are not exceeded. The second is to gather data related to
the sources of exposure and the effectiveness of control measures to ensure that optimum
conditions of protection are maintained.
75. The necessity of individual monitoring should be determined through measurements
which indicate whether the sum of exposure components exceeds 0.3 of the dose limit (Working
Condition A as defined in ZCRP Publications 26 and 35). Additional information on the
necessity of monitoring has been given in ZCRP Publication 35 and is not further elaborated
here.
6.1. Air Monitoring
76. Air monitoring serves two purposes for monitoring in mines. In addition to indicating
miners’ exposure, it constitutes a check on the effectiveness of existing control measures and
provides data needed for an orderly and optimum extension of controls during the expansion of
mine areas.
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18
REPORT
OF COMMITTEE
4
6.3. Monitoring the Quality of Protective Measures Systems
83. One of the principal purposes for monitoring in mines is to gather the data necessary to
evaluate the effectiveness of control measures and to ensure that optimum conditions of
protection are maintained. The types of measurements to be made are similar to those made to
ensure compliance with the individual dose limits, but the results are applied in a different
manner.
84. Systematic measurements of external dose rates, potential alpha energy concentrations of
radon decay products and concentrations of ore dust should be made to detect as soon as
possible deviations from previously selected reference levels (see paragraph 44). The frequency
of these measurements should depend on the probability of exceeding the reference levels.
Deviations will usually be indicative of a degradation in the protective measures, such as air
cleaning and ventilation, and should result in investigation and corrective actions.
85. Other types of monitoring, related to assessment of the performance of protective
measures systems, such as determinations of primary and secondary ventilation air flow rates,
while not radiation protection measurements per se, will also be useful in maintaining
acceptable working conditions by providing an immediate measure of system performance
which can be compared with the design criterion. It should be remembered that even small
deviations from the design could result in poor ventilation in some areas of the mine, with a
consequent large potential for overexposure.
86. In addition to the monitoring performed to evaluate system operations, measurements of
the basic variables that influence exposure, such as ore grade, radon exhalation into the mine air,
and the radium content of mine water, will be useful in ensuring that the design of protective
systems is adequate. Such measurements should also be made on a routine basis, since these
variables will change during the normal development of mining operations.
7. MEDICAL
SURVEILLANCE
87. The Commission, in ZCRP Publication 26, paragraph
medical surveillance:
184, has defined the objectives of
-to
-to
assess the health of the worker;
help in ensuring initial and continuing compatibility between the health of the workers
and the conditions of their work;
-to provide a base line of information useful in the case of accidental exposure or
occupational disease.
88. In achieving these aims, the physician must comply with the procedures which are based
on the general principles of occupational medicine, and which are commonly used for the
medical surveillance of workers exposed to ionizing radiation. Appropriate information is given
in a joint report of IAEA, WHO and ILO. l3 The physician must also take into consideration the
specificity of working conditions and potential hazards in mines. It must be emphasized that
ionizing radiation is only one of the occupational hazards faced in mining.
89. Where there is a radiation hazard in an underground mine, it will probably be due to high
air concentrations of radon and its decay products. Any respiratory disease, such as chronic
bronchitis, or smoking, may increase the risk of the development of a carcinoma of the lung:
these facts should be drawn to the worker’s attention.
90. The medical surveillance of miners in regard to pulmonary function must be extremely
RADIATION
PROTECTION
OF WORKERS
19
IN MINES
careful and should include, either as regular examinations or as special investigations, chest
radiography, respiratory function tests and sputum cytology.
ANNEX
SPECIAL QUANTITIES
AND UNITS
In Annex B of ICRP Publication 32, detailed explanations are given concerning those special
quantities and units which are used in the case of radon, thoron and their decay products.
The main definitions are presented below.
Potential cI energy
The potential u energy, sp, of an atom is the total a energy emitted during the decay of this atom
along the decay chain down to *“Pb(RaD) or *“Pb respectively. The total potential a energy
per Bq of activity of a radionuclide becomes EJ&, where the decay constant II, is expressed in
S - ‘. Values of E, and cp/A are listed in Table A. 1.
Table A.l. Potential
a energy per atom and per Bq
Potential
Radionuclide
per atom (Q
(lo-l2
(MeV)
J)
t( energy
per Bq &/A,)
(lo-”
(MeV)
J)
ZZZRn(Rn)
“*Po(RaA)
‘14Pb(RaB)
2’4Bi(RaC)
Z’4Po(RaC’)
19.2
13.7
7.69
7.69
7.69
3.07
2.19
1.23
1.23
1.23
9.15 lo6
3 620
17 800
13 100
2.0 lo’-3
14 700
5.79
28.6
21.0
3.0 10-e
“‘Rn(Tn)
‘16Po(ThA)
‘l’Pb(ThB)
212Bi(ThC)
“‘Po(ThC’)
20.9
14.6
7.80
7.80
8.78
3.34
2.34
1.25
1.25
1.41
1660
3.32
4.31 105
4.09 lo4
3.85 1O-6
2.65
5.32 1O-3
691
65.6
6.2 1O-9
Potential a-energy concentration in air
The potential a-energy concentration of any mixture of short-lived ***Rn or **‘Rn decay
products is the sum of the potential alpha energy of all decay product atoms present per unit
volume of air. If C,,i is the activity concentration of a decay product nuclide i in air, the potential
alpha-energy concentration, C,, of the decay product mixture becomes:
summed over all short-lived decay products down to 210Pb or *“Pb respectively.
In Table A.2 the conversion factors between activity concentration (in Bq m-“) and potential
cc-energy concentration are listed for the short-lived decay product nuclides of ***Rn and 220Rn
with three different units.
Equilibrium-equivalent radon concentration (EC,,,) and equilibrium factor (F)
The E& of a non-equilibrium mixture of short-lived radon decay products in air is that
activity concentration of radon in radioactive equilibrium with its short-lived decay products
20
REPORT
Table A.2. Potential
Radionuclide
*16Po(ThA)
=*Pb(ThB)
*12Bi(ThC)
* 1*Po(ThC’)
OF COMMITTEE
a-energy
4
concentration
per Bq
mm3
MeV I-’
1O-1o J mm3
10-e WL
3.62
11.8
13.1
2.0 1o-6
5.19
28.6
21.0
3.0 10-6
21.8
137
101
1.6 lo-’
3.32 1O-3
431
40.9
3.85 1O-9
5.52 lo-”
691
65.6
6.2 1O-9
0.0256
3 320
315
3.0 lo-*
that has the same potential a-energy concentration, CP9as the non-equilibrium mixture to which
the EC&, refers.
The “equilibrium factor”, F, with respect to potential a energy is defined as the ratio of the
EC& to the actual activity concentration G,, of radon in air:
Activity and potential a-energy exposure (E)
The “activity exposure” of an individual to ***Rn or **ORn is the time integral over the
activity concentration of ***Rn or **‘Rn, respectively, to which the individual is exposed during
a definite period of time. Its unit is, for example, Bq h m - 3.
The “potential a-energy exposure” of an individual to short-lived 222Rn or **‘Rn decay
products is the time-integral over the potential alpha-energy concentration of the decay product
mixture to which the individual is exposed during a definite period of time. This quantity can be
expressed in J h mV3.
Activity and potential a-energy intake by inhalation
The “potential a-energy intake” of an individual by inhalation of radon decay products is the
inhaled potential alpha energy of the decay product mixture during a definite period of time. If u
is the mean breathing rate during this period, the potential alpha-energy intake, Z,, is related to
the potential alpha-energy exposure, Z$ by the equation:
Table A.3. Conversion factors between activity
(&) and potential a-energy intake (I& of “‘Rn
**‘Rn decay products
I#ORadionuclide
*‘sPo(RaA)
214Pb(RaB)
*‘&Bi(RaC)
‘16Po(ThA)
“‘Pb(ThB)
2’2Bi(ThC)
lo J)
I,(Bq)
5.8
28.6
21.0
0.0053
691
65.6
intake
and
IdlO’ Bq)
Z,,(J)
17.2
3.50
4.16
18900
0.145
1.52
RADIATION PROTECTION OF WORKERS IN MINES
21
“Activity intake” by inhalation is the inhaled activity of a radionuclide during a definite period
of time. The activity intake, I,, and the potential E-energy intake, Z,, of a decay product of “‘Rn
or 220Rn are related by:
Z, = (~#4~ 1,
The conversion factor, EJ&, is the potential ctenergy per unit of activity of the decay product
being considered, which is given in Table A. 1. The rounded values for the ratios (Z,,/Z.)and (Z,/Z,)
given in Table A.3 are recommended for practical purposes.
REFERENCES
1. ICRP Publication 24. Radiation
protection
in uranium and other mines. A report of Committee
4 of the
International
Commission
on Radiological
Protection.
Annals ofthe ICRP 1, No. 1, Pergamon Press (1977).
2. ICRP Publication 26. Recommendations
of the International
Commission
on Radiological
Protection.
Annals of
the ICRP 1, No. 3, Pergamon Press (1977).
3. ICRP Publication 30. Limits for intakes of radionuclides
by workers. Annuls ofthe ICRP 2, No. 3/4,3, Nos l-4,4,
No. 3/4, 5, Nos 14, 6, No. 2/3, 7, Nos l-3, 8, Nos l-3, 8, No. 4, Pergamon
Press (1979-1982).
4. ICRP Publication 32. Limits for inhalation of radon daughters by workers. Annals ofthe ICRP 6, No. 1, Pergamon
Press (1982).
5. ICRP Publication 35. General principles of monitoring for radiation protection of workers. Annals of the ICRP9,
No. 4, Pergamon Press (1982).
6. United Nations Scientific Committee on the Effects of Atomic Radiation. Ionising radiation: sources and biological
effects. 1982 Report to the General Assembly, New York, United Nations (1982).
7. Infernational
Conference on Radiation Hazards in Mining: Control, Measurements and Medical Aspects, Golden
(USA), October 4-9, 1981. (M. Gomez, ed.), New York, Society of Mining Engineering (1981).
8. Internarional Conference on Occupational Radiation safety in Mining. Toronto, October 14-18, 1984. (H. Stocker,
ed.), Toronto, Canadian Nuclear Association (1985).
9. ICRP Publication 37. Cost-benefit
analysis in the optimization of radiation protection. Annals ofthe ICRP 10,No.
2/3, Pergamon Press (1983).
IO. OECD-NEA.
Dosimetry aspects of exposure to radon and thoron daughter products. Report by a Group of
Experts of the OECD Nuclear Energy Agency, OECD, Paris (1983).
11. Johnson, J. R. A review of the dosimetry from inhalation of long-lived alpha activity in ore dust. In: Occupational
Radiation &fery in Mining, Vol. 1,495-502, Toronto, October 1418, 1984. (H. Stocker, ed.), Toronto, Canadian
Nuclear Association (1985).
12. OECD-NEA.
Metrology and monitoring
of radon, thoron and their daughters. Report by a Group of Experts of
the OECD Nuclear Energy Agency, SAN/DOC (84) 6, Paris (1984).
13. IAEA, WHO and ILO. Radiation and occupational
health: A training manual for occupational
physicians. Joint
report in press (IAEA).
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Annals of the ICRP
Aims and Scope
Founded in 1928, the International
5
Commission on Radiological Protection has, since 1950,
been providing general guidance on the widespread use of radiation sources caused by
developments in the field of nuclear energy.
;
3
The reports and recommendations of the ICRP are available in the form of a review journal,
Annals of the ICRP. Subscribers to the journal will receive each new report as soon as it
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Publications of the
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Full details of all ICRP reports can be obtained from your nearest Pergamon
Published reports of the ICRP
ICRP Publication 47 (Annals of the ICRP Vol. 16 No.
Radiation Protection of Workers in Mines
Waste
ICRP Publication 44 (Annals of the ICRP Vol. 15 No. 2)
Protection of the Patient in Radiation Therapy
ICRP Publication No. 43 (Annals of the ICRP Vol. 15 No.
Principles of Monitoring
for
the Radiation Protection of the
ICRP Publication No. 42 (Annals of the ICRP Vol. 14 No. 4)
A Compilation of the Major Concepts and Quantities in use by ICRP
Nonstochastic Efibcts of Ionizing
Radiation
ICRP Publication No. 40 (Annals of the ICRP Vol. 14 No.
0 08 034020
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0 08 033666
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5
0 08 032336
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ICRP Publication No. 41 (Annais ol the ICRP Vol. 14 No.
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ICRP F'ublication 46 (Annals of the ICRP Vol. 15 No. 4)
Radiation Protection Principles for the Disposal of Solid Radioactiue
ICRP Publication 45 (Annals of the ICRP Vol. 15 No. 3)
Quantitatiue Bases for Deueloping a Unified Index of Harm
5
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3)
2)
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Protection of the Public in the Euent of Major Radiation Accidents: Principles
for Planning
0 08 032302
ICRP Publication No. 39 (Annals of the ICRP Vol. 14 No. l)
Principles for Limiting Expo5yyB of the Public to Natural Sources of Radiation 0 08 031503
ICRP Publication No. 38 (Annals of the ICRP Vols. 1l-13)
(Hardcover) 0 08 030760
Radionuclide Transformatiins: Energy anrl Intensity of Emisiions
(Flexicover) 0 08 030761
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ICRP Publication No. 37 (Annals of the ICRP Vol. 10 No. 2/3)
Cost-Benefit Analysis in the Optimization of Radiation
Protection
0 08 029817
6
ICRP Publication No. 36 (Annals of the ICRP Vol. 10 No. l)
Protection against Ionizing Radiation in the Teaching of
Science
0 08 029818 4
ICRP Publication No. 35 (Annals of the ICRP Vol. 9 No. 4)
0 08 029816 8
General Principles of Monitoring for Radiation Protection of Il'orkers
trCRP Publication No. 34 (Annals of the ICRP Vol. 9 No. 2/3)
0 08 029797 8
Protection of the Patient in Diagnostic Radiology
ICRP Publication No. 33 (Annals of the ICRP Vol. 9 No. 1)
Protection Against lonizing Radiation.from External Sources Used in Medicine 0 08 029779 X
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(Continued on inside back cover)
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