Metal/Nonmetal Health Inspection Procedures Handbook PH06-IV-1(1)
October 2006 10-1
Chapter 10
IONIZING RADIATION
I. Introduction
This chapter includes sampling procedures for evaluating four types of ionizing radiation
hazards
: alpha, beta, gamma, and x-ray. Ionizing radiation can cause cancer. At high
doses, ionizing radiation causes radiation sickness. Ionizing radiation can be emitted by
the mined ore, the surrounding rock, or nuclear gauges such as those that monitor the
flow of materials. Miners can be exposed to hazardous levels of ionizing radiation at
mines other than those producing radioactive minerals.
II. Definitions
Alpha Counter/Scaler
- an instrument that counts alpha decay events when used with a
scintillation detector.
Alpha Radiation
- a particle that has a positive (+2) charge and is emitted from the
nucleus of an atom. An alpha particle consists of two protons and two neutrons. When
inhaled, dust containing alpha producing particles can cause lung cancer. While alpha
particles travel at a high energy rate, they are so large that a sheet of paper or a few
centimeters of air can block their path. Alpha particles are emitted by radon, uranium,
and thoron. Examples of alpha emitters are uranium-238, radium-226, and radon-222.
Beta Radiation
- a particle that has a negative (-1) charge and is emitted from the
electron shell of an atom. A beta particle consists of one electron. Beta radiation has
more penetrating capability than alpha radiation because the particle is much smaller.
Even so, a light-weight barrier material, such as cardboard or sheet metal, can block beta
radiation.
Gamma Radiation
- short wavelength electromagnetic radiation emitted from
radioactive elements such as uranium. Lead or concrete can block this type of radiation.
Geiger-Mueller counter
- small hand-held meter designed to measure x-ray and gamma
radiation.
Half-life
- the time required for a radioactive substance to lose 50 % of its activity by
decay. Each radionuclide has a characteristic half-life.
Ionizing Radiation
- a form of energy capable of changing a stable, electrically-neutral
atom into an unstable electrically-charged particle (ion). Radiation from uranium, radon,
and other radioactive sources is ionizing.
Metal/Nonmetal Health Inspection Procedures Handbook PH06-IV-1(1)
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Isotope
- a form of an element that differs from other forms of the same element in the
number of neutrons in each atom’s nucleus. Isotopes of the same element may have
different levels of stability and potential radioactivity.
Kusnetz method -
a method for determining exposure to alpha radiation emitted from
radon and thoron daughters/progeny. It was developed in the 1950's by H. L. Kusnetz.
Radioactive decay
- the natural process of a radioactive material shedding mass from its
nucleus. After each decay event, another element or isotope of lesser mass is formed.
The decay process trends toward more stable elements with elemental lead (Pb 207) the
most stable.
Radon
- the radioactive gas produced by the radioactive decay of the element radium.
Radon Daughters/Radon Progeny
- unstable, short-lived decay products of radon gas
which emit alpha particles during the decay process. (Terms are used interchangeably.)
REM
- abbreviation of Roentgen Equivalent Man - a unit for measuring the absorbed
dose by humans (and biological effects) of ionizing radiation. Personal exposure limits
for gamma and X-Ray radiation are expressed in REMs.
Roentgen (R)
- a unit for measuring X-rays or gamma rays. For radiation protection, one
R equals the dose measurement of one REM.
Scintillation detector
- type of detector used to determine alpha emissions from filter
samples. Operates as photons are released from a zinc sulfide phosphor and amplified
with a photo-multiplier tube. Works in train with an alpha scaler/counter.
Thoron
- a gas formed from the radioactive decay of thorium (Th), an element. Thoron
is similar to radon as a health hazard in that respirable thoron daughters/progeny emit
alpha radiation. It is an isotope of radon gas.
Working level (WL)
- the unit of measurement of airborne radon or thoron alpha
particles in an area. Working levels are used to express the concentrations of radon
daughters in underground mines for compliance sampling. It is calculated by the
general formula:
WL = Radiation Level X Time (hours)
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Working level months (WLM)
- the unit of measurement for determining compliance
with the annual exposure limit for miners. A lung dose of 10 REM is equal to 1.0 WLM.
For compliance determination, 30 CFR § 57.5040 requires WLM be calculated by the
following formula:
WLM = Number of hours exposed in a month X average WL
173 hours per month
X-ray radiation
- is similar to gamma radiation in that it is a ray and not a particle but
different in that it is man-made versus naturally-occurring radiation. X-rays are produced
when a focused electron beam is aimed at a Tungsten surface resulting in an emanation of
high energy, highly penetrating radiation. Lead or thick concrete can block this type of
radiation.
III. Standards Applicable to Ionizing Radiation
A. Exposure Limits
Title 30 CFR §§ 57.5037 through 57.5047 contain the ionizing radiation exposure
limits for miners:
1.
Miners shall not be exposed to air having a radon daughter concentration
exceeding 1.0 working level (WL) in active workings.
2.
Ventilation is the primary means for controlling radon daughters to below
the allowable exposure limits. However, respirators approved by NIOSH
for radon daughters shall be used in atmospheres whose radon daughter
concentrations exceed 1.0 WL.
3.
If the WL concentration exceeds 10 WL, protection against radon gas
shall be provided by supplied air devices or by face masks containing
absorbent material capable of removing both radon and its daughters.
4.
No miner shall be exposed to more than 4.0 WLM in any calendar year.
5.
Annual individual gamma radiation exposure shall not exceed 5 REMs.
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B. Sampling requirements
1. Underground Non-Uranium Mines
a. Screening Frequency
- Annually sample all metal and nonmetal
mines where radon daughters have exceeded 0.1 WL in the past,
per 30 CFR § 57.5037(a). Sample remaining nonmetal and stone
mines every three years. Sample new or reopened mines as soon
as possible. Sample exhausts (return airways) and poorly
ventilated areas for radon daughters. Where any screening sample
exceeds 0.1 WL, follow the additional procedures below.
b. Concentration 0.1 WL
- Sample all active work areas four times
annually (Full-Time Permanent - FTP) or whenever conducting a
regular inspection (Intermittent - INT). Also evaluate the mine
operator's (quarterly) sampling procedures for possible
inadequacies.
Monitor mine operator compliance with 30 CFR §§ 57.5037(a)(2),
57.5038, 57.5039, 57.5040(a)(2), 57.5041, 57.5044, 57.5045, and
57.5046 where radon/thoron daughters concentrations exceed 0.3
WL.
Check the mine operator's sampling records and thoroughly sample
any work area exceeding 0.3 WL. A mine operator may invoke the
five consecutive week provisions of 30 CFR §§ 57.5037 and
57.5040. If MSHA sampling verifies the mine operator's claims
that alpha emissions have remained under 0.3 WL, the operator
can suspend weekly sampling in favor of quarterly sampling.
However, the mine operator must continue weekly sampling and
worker exposure record keeping if MSHA results exceed 0.3 WL.
2. Underground Uranium Mines
a. Sampling Frequency
- Sample all active work areas for both
radon and thoron daughters four times annually or whenever a
regular inspection is conducted. Also, monitor compliance with
30 CFR §§ 57.5037 and 57.5040. Where any sample exceeds 0.1
WL, follow the additional procedures below:
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b. Concentration 0.1 WL
- Evaluate the mine operator's sampling
procedures and employee exposure records to verify conformity to
the standard.
Monitor mine operator compliance with 30 CFR §§ 57.5037,
57.5038, 57.5039, 57.5041, 57.5044, 57.5045 and 57.5046 where
radon daughters concentrations exceed 0.3 WL.
Check the mine operator's sampling records and thoroughly sample
the area in question if an operator invokes the five consecutive
week provisions of 30 CFR §§ 57.5037 and 57.5040. If MSHA
sampling verifies the operator's findings, the mine operator can
revert to biweekly sampling. If MSHA sampling results exceed
0.3 WL, however, the operator must continue weekly sampling.
c. Screening for Gamma Radiation
- Perform annual gamma
radiation screening in all underground mines where radioactive
ores are mined. Monitor compliance with 30 CFR § 57.5047.
• Average readings in excess of 2 milliroentgens per hour
(mR/hr) require implementation of personal dosimeters for
all persons affected. Note: 2 milliroentgens per hour is
equivalent to 2 millirems per hour.
• Perform calculation presented in Appendix to obtain
projected shift exposure. Multiply projected shift exposure
by the number of shifts per week if doing a one day
screening and divide by 1000 to obtain estimated REM
value for a work week. Compare this calculation with
records to check the consistency of recorded exposures
with calculated exposures. Any significant discrepancy
should be investigated.
• Records of cumulative individual exposures should be
checked to ensure compliance with 5 REM annual
exposure limit.
• Failure to provide personal dosimeters and keep records of
cumulative individual exposures are citable offenses when
circumstances require, (see item 1 above.)
Sampling Uranium Mines
1. For radon samples, select locations that are most representative of the
miner’s average exposure.
2. When in doubt, sample all prominent work stations, giving priority to the
face and out of the way work areas
. Take representative samples in all
active stoping areas, travelways, shops, lunch rooms, and other occupied
mine areas.
C. Guidelines for Enforcement Sampling For Alpha Radiation
1. Follow the sampling strategies outlined in paragraphs A. and B. above.
2. Check air currents at the sampling locations for unusual conditions, using
a smoke-cloud producing apparatus and/or anemometer.
3. Measure and record the ventilation quantity at the time and place of
sampling.
4. Take ample notes regarding all conditions which might affect radon
daughter concentrations in the areas sampled.
5. Follow good sampling procedures.
6. Take all possible precautions to maintain the integrity of the calibration
sampling equipment.
7. Take as many samples as necessary to determine compliance with the
applicable standard and to establish an appropriate time limit for the
abatement of any citations which are issued.
D. Collecting the Sample
1. Pump and Filter Sampling Combination Kusnetz Method
a. Calibrate sampling pump at 2.0 Lpm or more (up to the stable limit
of your personal sampling pump), using the procedures in Chapter
4, and calibrate the readout instrument.
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