INSTRUCTION CONCERNING RISKS FROM OCCUPATIONAL RADIATION EXPOSURE
A. INTRODUCTION
This document is intended to be one of several possible sources of information that The University of Chicago is required by 32 Illinois Administrative Code Chapter II, Part 400 "Notices, …." to make available to its employees who work with radioactive materials. In it we borrow heavily from the United States Nuclear Regulatory Commission's Regulatory Guide 8.29 "Instruction Concerning Risks from Occupational Radiation Exposure". We have updated certain sections to reflect the current regulations of our Illinois Agreement State regulatory body the Illinois Department of Nuclear Safety. While some of the material has been extracted more or less intact from the Regulatory Guide, some sections have been deleted and others substantially modified to reflect our understanding of the current thinking on risk associated with low level radiation exposure.
B. DISCUSSION
It is known that exposure to high levels of ionizing radiation can cause biological effects that are harmful to the exposed organism. At lower levels of exposure these effects have not been observed in humans, but may occur at rates so low that they have not been statistically detected in studies involving exposed populations. To be conservative for radiation protection purposes it is assumed for the purpose of establishing regulatory limits that the rates of delayed effects from exposure to low level radiation is proportional to the dose. The observed effects at high exposures is then used to estimate the effects at low exposure. This is the so call "Linear No Threshold Model". Health effects from exposure to ionizing radiation are classified into three categories:
Somatic Effects: Effects occurring in the exposed person that, in turn, may be divided into two classes:
Prompt effects that are observable soon after a large or acute dose (e.g., 100 rems or more to the whole body in a few hours), and
Delayed effects such as cancer that may occur years after exposure to radiation.
Genetic Effects: Abnormalities that may occur in the future children of exposed individuals and in subsequent generations. Note: Genetic effects exceeding normal incidence have not been observed in any of the studies of exposed humans.
Teratogenic Effects: Effects that may be observed in children who were exposed during the fetal and embryonic stages of development.
Concerns about these biological effects have resulted in controls on doses to individual workers and in efforts to control the collective dose (person-rems) to the worker population. The controls are made on the basis of risk estimates.
At the relatively low levels of occupational radiation exposure in the United States, it is difficult, if not impossible, to demonstrate a relationship between exposure and effect. There is considerable uncertainty and controversy regarding estimates of radiation risk. In the appendix to this guide, a range of risk estimates is provided (see Table 1). Information on radiation risk has been included from such sources as the 1980 National Academy of Sciences' Report of the Committee on the Biological Effects of Ionizing Radiation (BEIR-80), the International Commission on Radiological Protection (ICRP) Publication 27 entitled "Problems in Developing an Index of Harm," the 1979 report of the science work group of the Interagency Task Force on the Health Effects of Ionizing Radiation, the 1977 report of the United Nations Scientific Committee on the Effects of Atomic Radiation (UNSCEAR report), and numerous published articles (see the bibliography to the appendix).
INSTRUCTION CONCERNING RISKS FROM OCCUPATIONAL RADIATION EXPOSURE
1. What is meant by risk?
Risk can be defined in general as the probability (chance) of injury, illness, or death resulting from some activity. However, the perception of risk is affected by how the individual views its probability and its severity. The intent of this document is to provide estimates of and explain the basis for possible risk of injury, illness, or death resulting from occupational radiation exposure. (See Questions 9 and I 0 for estimates of radiation risk and comparisons with other types of risk.)
Controversy in the scientific community exists over the application of risk estimators. This stems in part from the different types of applications for risk estimators, and also from the perspective of the scientists. Risk estimators can be applied in at least three ways:
In establishing regulatory exposure limits to protect the public and work force, it is desirable to use an appropriately conservative risk estimate so that adequate protection from harm is achieved. In our opinion the Linear No Threshold Model is adequate for this purpose. Most of the debate over the use of this model is between scientists who believe it is accurate and those who believe it to be overly conservative. Only a few believe that it may underestimate the risks, and we know of no accepted studies indicating that the linear model underestimates the risk.
In evaluating the probability of causation of an observed illness, it is also appropriate to use the Linear No Threshold Model since that is the basis of the regulatory limits. If the employer can demonstrate that the exposure receive by the employee is within the regulatory limits, then the probability of causation calculated should be small compared to the natural probability of getting the illness.
In estimating the probability that an exposed individual or population will develop illness related the exposure, it is, in our opinion, scientifically improper to apply any of the existing models. This is because none of the proposed risk estimators can be demonstrated with existing data to be applicable at low dose. In fact, some scientists claim that there is a dose below which there is no harmful effects. There are also some highly controversial studies that claim a small health benefit from low level exposure (radiation hormesis).
The debate among radiation professionals is likely to remain for the foreseeable future. At low exposures the risks or lack thereof calculated are so small compared to the natural incidence rate of illnesses that radiation can cause that it require huge exposed populations and control groups to generate the required statistical power to show any deviation from the natural rate. Confounding this even more is the variation of cancer rate as a function of location. This can occur for a variety of reasons: other environmental causes, difference in typical lifestyles, different population age distributions etc.
To demonstrate the difficulty, the increase in cancers observed in the total Hiroshima and Nagasaki survivor study cohort was only 5% greater than the expected natural rate as of 1985. According to 1985 American Cancer Society data shows a +/- 20% variability in cancer death rate by state in the United States. One might ask the question, do areas of the country with higher backgrounds have higher cancer rates? The answer is no, in fact there is an inverse correlation. Does this show that low exposures to radiation is beneficial? No, unfortunately this is an example of what epidemiologists call the "ecological fallacy". It is impossible to know the individual exposures received by these populations, and the confounding factors mentioned earlier may play a larger role than the radiation exposure. For example, low background areas tend to be located at low altitude where large industrial cities are located. These areas may exposed to higher levels of other carcinogens from pollution that over shadow any detrimental effects of low level radiation exposure
The biological effects that are known to occur after exposure to high doses (hundreds of rems 2) of radiation are discussed early in the document; discussions of the estimated risks from the low occupational dose (<S rems per year) follow. It is intended that this information will help develop an attitude of healthy respect for the risks associated with radiation, rather than unnecessary fear or lack of concern.
2. What are the possible health effects of exposure to radiation?
Some of the health effects that exposure to radiation may cause are cancer (including leukemia), birth defects in the future children of exposed parents, and cataracts. 3 These effects (with the exception of genetic effects) have been observed in studies of medical radiologists, uranium miners, radium workers, and radiotherapy patients who have received large doses of radiation. Studies of people exposed to radiation from atomic weapons have also provided data on radiation effects. In addition, radiation effects studies with laboratory animals have provided a large body of data on radiation-induced health effects, including genetic effects.
The observations and studies mentioned above, however, involve levels of radiation exposure that are much higher (hundreds of rems) than those permitted occupationally today ( <5 rems per year). Although studies have not shown a cause-effect relationship between health effects and current levels of occupational radiation exposure, it is prudent to assume that some health effects do occur at the lower exposure levels.
3. What is meant by prompt effects, delayed effects, and genetic effects?
Prompt effects are observable shortly after receiving a very large dose in a short period of time. For example, a whole-body 4 dose of 450 rems (90 times the annual dose limit for routine occupational exposure) in an hour to an average adult will cause vomiting and diarrhea within a few hours; loss of hair, fever, and weight loss within a few weeks; and about a 50 percent chance of death within 60 days without medical treatment. At doses less than about 100 rem (100,000 mrem) no clinical symptoms of prompt effects are observed. It may be possible to detect radiation exposures at the 10 rem level or below through clinical blood tests. However at these levels, no ill effects are felt.
Delayed effects, such as cancer, may occur years after exposure to radiation.
Genetic effects can occur when there is radiation damage to the genetic material. These effects may show up as birth defects or other conditions in the future children of the exposed individual and succeeding generations, as demonstrated in animal experiments. However, excess genetic effects clearly caused by radiation have not been observed in human populations exposed to radiation. It has been observed, however, that radiation can change the genes in cells of the human body. Thus, the possibility exists that genetic effects can be caused in humans by low doses even though no direct evidence exists.
4. In worker protection, which effects are of most concern to the regulatory agencies?
The main concern to the NRC and IDNS is the delayed incidence of cancer. The chance of delayed cancer is believed to depend on how much radiation exposure a person gets; therefore, every reasonable effort should be made to keep exposures low.
Immediate or prompt effects are very unlikely since large exposures would normally occur only if there were a serious radiation accident. Accident rates in the radiation industry have been low, and only a few accidents have resulted in exposures exceeding the legal limits. The probability of serious genetic effects in the future children o workers is estimated in the BIER 5 report, based on animal studies, at less than one-third that of delayed cancer (5-65 genetic effects per million rems compared to 160-450 cancer cases). A clearer understanding of the cause-effect relationship between radiation and human genetic effects will not be possible until additional research studies are completed.
5. What is the difference between acute and chronic?
Acute radiation exposure, which causes prompt effects and may also cause delayed effects, usually refers to a large dose of radiation received in a short period of time; example, 450 rems received within a few hours or less. The effects of acute exposures are well known from studies radiotherapy patients, some of whom received whole-body doses; atomic bomb victims; and the few accidents that have occurred in the early days of atomic weapons and reactor development, industrial radiography, and nuclear fuel processing. There have been few occupational incidents that have resulted in large exposures. NRC data indicate that, on the average, 1 accidental overexposure in which any acute symptoms are observed occurs each year. Most of these occur in industrial radiography and involve exposures of the hands rather than the whole body.
Chronic exposure, which may cause delayed effects not prompt effects, refers to small doses received repeatedly over long time periods; for example, 20-100 mrem (a mrem is one-thousandth of a rem) per week every week several years. Concern with occupational radiation risk primarily focused on chronic exposure to low levels
6. How does radiation cause cancer?
How radiation causes cancer is not well understood. It is impossible to tell whether a given cancer was caused radiation or by some other of the many possible causes. However, most diseases are caused by the interaction several factors. General physical condition, inherited traits, age, sex, and exposure to other cancer-causing agents such as cigarette smoke are a few possible contributing factors.
One theory is that radiation can damage chromosomes in a cell, and the cell is then directed along abnormal growth patterns. Another is that radiation reduces the body's normal resistance to existing viruses which can then multiply and damage cells. A third is that radiation activates an existing virus in the body which then attacks normal cells causing them to grow rapidly.
What is known is that, in groups of highly expose people, a higher than normal incidence of cancer is observed Higher than normal rates of cancer can also be produced laboratory animals by high levels of radiation. An increase incidence of cancer has not been demonstrated at radiation levels below the regulatory limits for exposure.
7. If I receive a radiation dose, does that mean I am certain to get cancer?
It is extremely unlikely that occupational radiation exposure will cause you to develop cancer. Even in the data from the survivors of Hiroshima and Nagasaki there is only a slight elevation in cancer rate, and even then only in the more highly exposed individuals. We know from studies of groups exposed to radiation, that at high exposures radiation is a carcinogen, but not a very good one.
Everyone gets a radiation dose every day (see Question 25), but most people do not get cancer. Even with doses of radiation far above legal limits, most individuals will experience no delayed consequences. There is evidence that some radiation damage can be repaired. The danger from radiation is much like the danger from cigarette smoke Only a fraction of the people who breathe cigarette smoke get lung cancer, but there is good evidence that smoking increases a person's chances of getting lung cancer. Similarly there is evidence that the larger the radiation dose, the larger the increase in a person's chances of getting cancer
Radiation is like most substances that cause cancer in that the effects can be seen clearly only at high dose. Estimates of the risks of cancer at low levels of exposure are derived from data available for exposures at high do levels and high dose rates. Generally, for radiation protection purposes these estimates are made using the linear model (Curve I in Figure 1). We have data on health effects at high doses as shown by the solid line in Figure 1. Below about 100 rems, studies have not been able to measure the risk, primarily because of the small numbers of exposed people and because the effect, if any, is small compared to difference in the normal incidence from year to year and place to place. Most scientists believe that there is some degree of risk matter how small the dose,(Curves I and 2). Some scientists believe that the risk drops off to zero at some low do (Curve 3), the threshold effect. A few believe that risk level off so that even very small doses imply a significant risk (Curve 4). The majority of scientists today endorse either the linear model (Curve 1) or the linear-quadratic model (Curve 2). While viewed skeptically by many, there are some who argue that there may actually be a slight health benefit to low level exposures. This is supported by some in vitro cell culture studies in which a low level pre-dose of radiation improved the survival rate of cells later exposed to high level radiation. It is thought that the low level exposure may trigger an increase in the cells' repair mechanisms which help them to repair damage more rapidly after the high dose. There are also some flawed environmental studies that show a health benefit, although these studies can't prove that the benefit was derived from the moderately higher radiation exposure.
The NRC endorses the use of linear model (Curve which shows the number of effects decreasing as the dose decreases, for radiation protection purposes. Again, this is for establishing regulatory limits and may or may not accurately reflect the actual risk. It is unlikely that the actual risk could be significantly greater than that predicted by the linear model or exposure studies would be able to measure the risk. If the actual risk is equal to or smaller than that predicted by the linear model, it will be difficult or perhaps even impossible to measure.
It is prudent to assume that smaller doses have some chance of causing cancer. This is as true for natural cancer causers such as sunlight and natural radiation as it is those that are man made such as cigarette smoke, smog, man-made radiation. If there is some chance that even very small doses may entail some small risk, it follows that no dose should be taken without a reason. Thus, a principle of radiation protection is to do more than merely meet the allowed regulatory dose limits; doses should be kept as low as is reasonably achievable (ALARA).
It is important to understand the probability factors here. A similar question would be: If you select one card from a full deck, will you get the ace of spades? This question cannot be answered with a simple yes or no. The best answer is that your chances are 1 in 52. However, if 1000 people each select one card from full decks, we can predict that about 20 of them will get an ace of spades. Each person will have 1 chance in 52 of drawing the ace of spades, but there is no way that we can predict which persons will get the right card. The issue is further complicated by the fact that in 1 drawing by 1000 people, we might get only 15 successes and in another perhaps 25 correct cards in 1000 draws. We can say that if you receive a radiation dose, you will have increased your chances of eventually developing cancer. It is assumed for regulatory purposes, that the more radiation exposure you get, the more you increase your chances of cancer.
Not all workers incur the same level of risk. The radiation risk incurred by a worker depends on the amount of dose received. Under the linear model explained above, a worker who receives 5 rems in a year incurs 10 times as much risk as another worker (the same age) who receives only 0.5 rem. The risk depends not only on the amount of dose, but also on the age of the worker at the time the dose is received. This age difference is due, in part, to the fact that a young worker has more time to live than an older worker, and the risk is believed to depend on the number of years of life following the dose. The more years left, the larger the risk. It should be clear that, even within the regulatory dose limits, the risk may vary a great deal from one worker. to another. Fortunately, only a very few workers receive doses near 5 rems per year; as pointed out in the answer to Question 19, the average annual dose for all radiation workers is less than 0.5 rem.
A reasonable comparison involves exposure to the sun's rays. Frequent short exposures provide time for the skin to repair. An acute exposure to the sun can result in painful burning, and excessive exposure has been shown to cause skin cancer. However, whether exposure to the sun's rays is short term or spread over time, some of the injury is not repaired and may eventually result in skin cancer. Also, it should be remembered that your body needs some exposure to sunlight. It is not healthful to avoid all exposure to light.
The effect upon a group of workers occupationally exposed to radiation may be an increased incidence of cancer over and above the number of cancers that would normally be expected in that group. Each exposed individual has an increased probability of incurring subsequent cancer. We can say that if 10,000 workers each receive an additional I rem in a year, we expect from the linear model for that group to be more likely to have a larger incidence of cancer than 10,000 people who do not receive the additional radiation. An estimate of the increased probability of cancer from low radiation doses delivered to large groups is one measure of occupational risk and is discussed in Question 9.
8. What groups of expert scientists have studied the risk from exposure to radiation?
In 1956, the National Academy of Sciences established advisory committees to consider radiation risks. The first of these was the Advisory Committee on the Biological Effects of Atomic Radiations (BEAR) and more recently it was renamed the Advisory Committee on the Biological Effects of Ionizing Radiation (BEIR). These committees have periodically reviewed the extensive research being done on the health effects of ionizing radiation and have published estimates of the risk of cancer from exposure to radiation (1972 and 1980 BEIR reports). The International Commission on Radiological Protection (ICRP) and the National Council on Radiation Protection and Measurement (NCRP) are two other groups of scientists who have studied radiation effects and published risk estimates (ICRP publication 26, 1977). These two groups have no government affiliation. In addition, the United Nations established an independent study group that published an extensive report in 1977, including estimates of cancer risk from ionizing radiation (UNSCEAR, 1977).
Several individual research groups or scientists such as Alice Stewart, E.S. Gilbert, T.F. Mancuso, T.W. Anderson, to name a few, have published studies concerning low-level radiation effects. The bibliography to this appendix includes several articles for the reader who wishes to do further study. The BEIR-80 report includes analysis of the work of many independent researchers.
9. What are the estimates of the risk of cancer from radiation exposure?
The cancer risk estimates (developed by the organizations identified in Question 8) are presented in Table 1.
In an effort to explain the significance of these estimates, we will use an approximate average of 300 excess cancer cases per million people, each exposed to I rem of ionizing radiation. If in a group of 10,000 workers each receives 1 rem, we could estimate that three would develop cancer because of that exposure, although the actual number could be more or less than three.
TABLE I
Estimates of Excess Cancer Incidence from Exposure
to Low-Level Radiation
Source Number of Additional a Cancers
Estimated to Occur in 1 million People
After Exposure of Each to 1 Rem of
Radiation
BEIR, 1980 160-450b
ICRP, 1977 200
UNSCEAR, 1977 150-350
a Additional means above the normal incidence of cancer.
b All three groups estimated premature deaths from radiation induced cancers. The American Cancer Society has recently stated that only about one half of all cancer cases are fatal. Thus, to estimate incidence of cancer, the published numbers were multiplied by 2. Note that the three groups are in close agreement on the risk of radiation-induced cancer.
The American Cancer Society has reported that approximately 25 percent of all adults in the 20. to 65-year age bracket will develop cancer at some time from all possible causes such as smoking, food, alcohol, drugs, air pollutants, and natural background radiation. Thus in any group of 10,000 workers not exposed to radiation on the job, we can expect about 2,500 to develop cancer. If this entire group of 10,000 workers were to receive an occupational radiation dose of 1 rem each, we could estimate that three additional cases might occur which would give a total of about 2,503. This means that a 1-rem dose to each of 10,000 workers might increase the cancer rate from 25 percent to 25.03 percent, an increase of about 3 hundredths of one percent.
As an individual, if your cumulative occupational radiation dose is 1 rem, your chances of eventually developing cancer during your entire lifetime may have increased from 25 percent to 25.03 percent. If your lifetime occupational dose is 10 rems, we could estimate a 25.3 percent chance of developing cancer. Using a simple linear model, a lifetime dose of 100 rems may have increased your chances of cancer from 25 to 28 percent. Almost all radiation workers at our university receive far less than 0.1 Rem (100 mrem) in one year from occupational sources. In fact the average film badge readings at the University are less than 0.01 Rem (10 mrem), however this omits exposures below the film badge threshold reading. However, from what we know about the properties of the film badges, the isotopes and activities used, and statistics our best estimate is that the average whole body exposure to laboratory personnel from occupational sources can be no more than a few tens of mrem and is probably less than 10 mrem per year.
The normal chance of developing cancer if you receive no occupational radiation dose is about equal to your chance of getting any spade on a single draw from a full deck of playing cards, which is one chance out of four. The additional chance of developing cancer from an occupational exposure of I rem is less than your chances of drawing an ace from a full deck of cards three times in a row.
Since cancer resulting from exposure to radiation usually occurs 5 to 25 years after the exposure and since not an cancers are fatal, another useful measure of risk is years of life expectancy lost on the average from a radiation-induced cancer. It has been estimated in several studies that the average loss of life expectancy from exposure to radiation is about 1 day per rem of exposure. In other words, a person exposed to I rem of radiation may, on the average, lose 1 day of life.
The words "on the average" are important, however, because the person who gets cancer from radiation may lose several years of life expectancy while his coworkers suffer no loss. The ICRP estimated that the average number of years of life lost in a given fatal industrial accident is 30 while the average number of years of life lost from. a fatal radiation-induced cancer is 10. The shorter loss of life expectancy is due to the delayed onset of cancer.
It is important to realize that these risk numbers are only estimates. Many difficulties are involved in designing research studies that can accurately measure the small increases in cancer cases due to low exposures to radiation as compared to the normal rate of cancer. There is still uncertainty and a great deal of controversy with regard to estimates of radiation risk. The numbers used here result from studies involving high doses and high dose rates, and they may not apply to doses at the lower occupational levels of exposure. The NRC and other agencies both in the United States and abroad are continuing extensive long-range research programs on radiation risk.
Some members of the National Academy of Sciences BEIR Advisory Committee and others feel that risk estimates in Table I are higher than would actually occur and represent an upper limit on the risk. Other scientists believe that the estimates are low and that the risk could be higher. However, these estimates are considered by the NRC staff to be the best available that the worker can use to make an informed decision concerning acceptance of the risks associated with exposure to radiation. A worker who decides to accept this risk should make every effort to keep exposure to radiation ALARA to avoid unnecessary risk. The worker, after all, has the first line responsibility for protecting himself from radiation hazards.
10. How can we compare radiation risk to other kinds of health risks?
Perhaps the most useful unit for comparison among health risks is the average number of days of life expectancy lost per unit of exposure to each particular health risk. Estimates are calculated by looking at a large number of persons, recording the age when death occurs from apparent causes, and estimating the number of days of life lost as a result of these early deaths. The total number of days of life lost is then averaged over the total group observed.
Several studies have compared the projected loss of life expectancy resulting from exposure to radiation with other health risks. Some representative numbers are presented in Table 2.
These estimates indicate that the health risks from occupational radiation exposure are smaller than the risks associated with many other events or activities we encounter and accept in normal day-to-day activities.
TABLE 2
Estimated Loss of Life Expectancy from Health Risks
Estimates of Days of Life Expectancy
Lost,
Health Risk Average
Smoking 20 cigarettes/day 2370 (6.5 years)
Overweight (by 20%) 985 (2.7 years)
All accidents combined 435 (1.2 years)
Auto accidents 200
Alcohol consumption (U.S. average) 130
Home accidents 95
Drowning 41
Natural background radiation, 8
calculated
Medical diagnostic x-rays (U.S. 6
average), calculated
AU catastrophes (earthquake, etc.) 3.5
1 rem occupational radiation dose, 1
calculated (industry average for
the higher-dose job categories is
0.65 rem/yr.)
1 rem/yr. for 30 years, calculated 30
10 mrem/yr. for 30 years, 0.3 (7 hours)
calculated
adapted from Cohen and Lee, "A Catalogue of Risks," Health
Physics, Vol. 36, June 1979.
A second useful comparison is to look at estimates of the average number of days of life expectancy lost from exposure to radiation and from common industrial accidents at radiation-related facilities and to compare this number with days lost from other occupational accidents. Table 3 shows average days of life expectancy lost as a result of fatal work-related accidents. Note that the data for occupations other than radiation related do not include death risks from other possible hazards such as exposure to toxic chemicals, dusts, or unusual temperatures. Note also that the unlikely occupational exposure at 5 rems per year for 50 years, the maximum allowable risk level, may result in a risk comparable to the average risks in mining and heavy construction.
Industrial accident rates in the nuclear industry and related occupational areas have been relatively low during the entire history of the industry (see Table 4). This is believed to be due to the early and continuing emphasis on tight safety controls. The relative safety of various occupational areas can be seen by comparing the probability of death by accident per 10,000 workers over a 40-year working lifetime. These figures do not include death from possible causes such as exposure to toxic chemicals or radiation.
TABLE 3
Estimated Loss of Life Expectancy from Industrial Hazards
Industry Type
Estimates of Days of Life Expectancy
Lost,-Average
All industry 74
Trade 30
Manufacturing 43
Service 47
Government 55
Transportation and, utilities 164
Agriculture 277
Construction 302
Mining and quarrying 328
Radiation accidents, death from <1
exposure
Radiation dose of 0.65 rem/yr. 20
(industry average) for 30 years,
calculated
Radiation dose of 5 rems/yr. for 50 250
years
Industrial accidents at nuclear 58
facilities (non-radiation)
Adapted from Cohen and Lee, "A Catalogue of Risk." Health Physics, Vol. 36, June 1979; and World Health Organization, Health Implications of Nuclear Power Production, December 1975.
TABLE 4
Probability of Accidental Death by Type of Occupation
Occupation Number of Accidental
Deaths for 10,000
Workers for 40 Years
Mining 252
Construction 228
Agriculture 216
Transportation and public 116
utilities
All industries 56
Government 44
Nuclear industry (1975 data excluding 40
construction)
Manufacturing 36
Services 28
Wholesale and trade 24
Adapted from National Safety Council, Accident Facts. 1979-, an Atomic Energy Commission, Operational Accidents and Radiation. Exposure Experience, WASH-1 192, 1975.
11. Can a worker become sterile or impotent from occupational radiation exposure?
Observation of radiation therapy patients who receive localized exposures, usually spread over a few weeks, has shown that a dose of 500-800 rems to the gonads can produce permanent sterility in males or females (an acute whole-body dose of this magnitude would probably result in death within 60 days). An acute dose of 20 rems to the testes can result in a measurable but temporary reduction in sperm count. Such high exposures on the job could result only from serious and unlikely radiation accidents. Although high doses of radiation can affect fertility, they have no effect on the ability to function sexually. Likewise, exposure to permitted occupational levels of radiation has no observed effect on fertility and also has no effect on the ability to function sexually.
12. What are the regulatory radiation dose limits?
32 Illinois administrative Code Chapter II, Part 340 SUBPART C: OCCUPATIONAL DOSE LIMITS
Section
340.210 Occupational Dose Limits for Adults
340.220 Compliance with Requirements for Summation of External and Internal Doses
340.230 Determination of External Dose from Airborne Radioactive Material
340.240 Determination of Internal Exposure
340.250 Determination of Prior Occupational Dose
340.260 Planned Special Exposures
340.270 Occupational Dose Limits for Minors
340.280 Dose to an Embryo/Fetus
SUBPART D: RADIATION DOSE LIMITS FOR INDIVIDUAL MEMBERS
OF THE PUBLIC
Section
340.310 Dose Limits for Individual Members of the Public
340.320 Compliance with Dose Limits for Individual Members of the Public
13. What is meant by ALARA?
In addition to providing an upper limit on a person's permissible radiation exposure, the regulatory agencies also requires that its licensees maintain occupational exposures as far below the limit as is reasonably achievable (ALARA). This means that every activity at a nuclear facility involving exposure to radiation should be planned so as to minimize unnecessary exposure to individual workers and also to the worker population. A job that involves exposure to radiation should be scheduled only when it is clear that the benefit justifies the risks assumed. All design, construction, and operating procedures should be reviewed with the objective of reducing unnecessary exposures.
14. Has the ALARA concept been applied if, instead of reaching, dose limits during the first week of a year, the worker's dose is spread out over the whole year?
No. For radiation protection purposes, the risk of cancer from low doses is assumed to be proportional to the amount of exposure, not the rate at which it is received. Thus it is assumed that spreading the dose out over time or over larger numbers of people does not reduce the overall risk. The ALARA concept has been followed only when the individual and collective doses are reduced by reducing the time of exposure or decreasing radiation levels in the working environment.
15. What is meant by collective dose and why should it be maintained ALARA?
Nuclear industry activities expose an increasing number of people to occupational radiation in addition to the radiation doses they receive from natural background radiation and medical radiation exposures. The collective occupational dose (person-rems) is the sum of all occupational radiation exposure received by all the workers in an entire worker population. For example, if 100 workers each receive 2 rems, the individual dose, is 2 rems and the collective dose is 200 person-rems. The total additional risk of cancer and genetic effects in an exposed population is assumed to depend on the collective dose.
It should be noted that, from the viewpoint of risk to a total population, it is the collective dose that must be controlled. For a given collective dose, the number of health effects is assumed to be the same even if a larger number of people share the dose. Therefore, spreading the dose out may reduce the individual risk, but not that of the population.
Efforts should be made to maintain the collective dose ALARA so as not to unnecessarily increase the overall population incidence of cancer and genetic effects.
16. Is the use of extra workers a good way to reduce risks?
There is a "yes" answer to this question and a "no" answer. For a given job involving exposure to radiation, the more people who share the work, the lower the average dose to an individual. The lower the dose, the lower the risk. So, for you as an individual, the answer is "yes."
But how about the risk to the entire group of workers? Under assumptions used by the NRC for purposes of protection, the risk of cancer depends on the total amount of radiation energy absorbed by human tissue, not on the number of people to whom this tissue belongs. Therefore, if 30 workers are used to do a job instead of 10, and if both groups get the same collective dose (person-rems), the total cancer risk is the same, and nothing was gained for the group by using 30 workers. From this viewpoint the answer is "no." The risk was not reduced but simply spread around among a larger number of persons.
Unfortunately, spreading the risk around often results in a larger collective dose for the job. Workers are exposed as they approach a job, while they are getting oriented to do the job, and as they withdraw from the job. The dose received during these actions is called nonproductive. If several crew changes are required, the nonproductive dose can become very large. Thus it can be seen that the use of extra workers may actually increase the total occupational dose and the resulting collective risks.
The use of extra workers to comply with the dose limits is not the way to reduce the risk of radiation-induced cancer for the worker population. At best, the total risk remains the same, and it may even be increased. The only way to reduce the risk is to reduce the collective dose; that can be done only by reducing the radiation levels, the working times, or both.
17. Why aren't there collective dose limits?
Compliance with individual dose limits can be achieved simply by using extra workers. However, compliance with a collective dose limit (such as 100 person-rems per year for a licensee) would require reduction of radiation levels, working times, or both. But there are many problems associated with setting appropriate collective dose limits.
For example, we might consider applying a single collective dose limit to all licensees. The selection of such a collective dose limit would be almost impossible because of the wide variations in collective doses among licensees. A power reactor could reasonably be expected to have an average annual collective dose of several hundred person rems. However, a small industrial radiography licensee could very well have a collective dose of only a few person rems in a year.
Even choosing a collective dose limit for a group of similar licensees would be almost as difficult. Radiography licensees as a group had an average collective dose in 1977 of 9 person-rems. However, the smallest collective dose for a radiography licensee was less than 1 person-rem, and the largest was 401 person-rems.
Setting a reasonable collective dose limit for each individual licensee would also be very difficult. It would require a record of all past collective doses on which to base such limits. Setting an annual collective dose limit would then amount to an attempt to predict a reasonable collective dose for each future year. In order to do this, it would be necessary to be able to predict changes in each licensed activity that would increase or decrease the collective dose. In addition, annual collective doses vary significantly from year to year according to the kind and amount of maintenance required, which cannot generally be predicted in advance. Following all such changes and revising limits up and down would be very difficult if not impossible. However, these efforts would be necessary if a collective dose limit were to be reasonable and help minimize doses and risks.
18. How are radiation dose limits established?
The NRC establishes occupational radiation dose limits based on guidance to Federal agencies from the Environmental Protection Agency (EPA) and, in addition, considers NCRP and ICRP recommendations. Scientific reviews of research data on biological effects such as the BEIR report are also considered.
For example, recent EPA guidance recommended that the annual whole-body dose limit be established at 5 rems per year and indicated that exposure, year after year, to 5 rems would involve a risk to a worker comparable to the average risks incurred by workers in the higher risk jobs such as mining. In fact, few workers ever reach such a limit, much less year after year, and the risks associated with actual exposures are considered by the EPA to be comparable to the safer job categories. A 5-rem-per-year limit would allow occasional high dose jobs to be done without excessive risk.
19. What are the typical radiation doses received by workers?
The NRC requires that certain categories of Licensees report data on annual worker doses and doses for all workers who leave employment with Licensees. Data were received on the occupational doses in 1977 of approximately 100,000 workers in power reactors, industrial radiography, fuel processing and fabrication facilities, and manufacturing and distribution facilities. Of this total group, 85 percent received an annual dose of less than 1 rem; 95 percent received less than 2 rems; fewer than I percent exceeded 5 rems in 1 year. The average annual dose of those workers who were monitored and had measurable exposures was about 0.65 rem. A study completed by the EPA, using 1975 exposure data for 1,260,000 workers, indicated that' the average annual dose for all workers who received a measurable dose was 0.34 rem.
Table 5 lists average occupational exposures for workers (persons who had measurable exposure above background levels) in various occupations, based on the 1975 data.
TABLES
U.S. Occupational Exposure Estimates a
Occupational Subgroup Average Whole-Body Dose Collective Dose
(millirems) (person-rems)
Medicine 320 51,400
Industrial Radiography 580 5,700
Source Manufacturing 630 2,500
Power Reactors 760 21,400
Fuel Fabrication and 560 3,100
Reprocessing
Uranium Enrichment 70 400
Nuclear Waste Disposal 920 100
Uranium Mills 380 760
Department of Energy 300 11,800
Facilities
Department of Defense 180 10,100
Facilities
Educational Institutions 206 1,500
Transportation 200 2,300
Adapted from Cook and Nelson, Occupational Exposures to Ionizing Radiation in the United States: A Comprehensive Summary for 1975, Draft, Environmental Protection Agency.
20. What happens if a worker exceeds the annual exposure limit?
Radiation protection limits are not absolute Limits below which it is safe and above which there is danger. Exceeding a limit does not imply that you have suffered an injury. A good comparison is with the highway speed limit, which is selected to limit accident risk and still allow you to get somewhere. If you drive at 75 mph, you increase your risk of an auto accident to levels that are not considered acceptable by the people who set speed limits, even though you may not actually have an accident. If a worker's radiation dose repeatedly exceeds the regulatory limits, the risk of health effects could eventually increase to a level that is not considered acceptable. Exceeding a protection limit does not mean that any adverse health effects are going to occur. It does mean that a Licensee's safety program has failed in some respect and that the appropriate regulatory agency and the licensee should investigate to make sure the problems are corrected.
If an overexposure occurs, the regulations prohibit any additional occupational exposure to that person during the remainder of the year in which the overexposure occurred. The licensee is required to file an overexposure report to the Illinois Department of Nuclear Safety and may possibly be subject to a fine, just as you are subject to a traffic fine for exceeding the speed limit. In both cases, the fines and, in some serious or repetitive cases, suspension of license are intended to encourage efforts to operate within the limits. The safest limits would be 0 mph and 0 rem per quarter. But then we wouldn't get anywhere.
21. Why do some facilities establish administrative limits that are below the regulatory limit?
There are two reasons. First, the regulations state that Licensees should keep exposures to radiation ALARA. By requiring specific approval for worker doses in excess of set levels, more careful risk-benefit analysis can be made as each additional increment of dose is approved for a worker. Secondly, a facility administrative limit that is set lower than the regulatory limit provides a safety margin designed to help the licensee avoid overexposures.
22 Several scientists have suggested that limits are too high and should be lowered What are the arguments for lowering the limits?
In general, those critical of present dose limits say that the individual risk is higher than is estimated by the BEIR Committee, the ICRP, and UNSCEAR. Based on studies of low-level exposures to large groups, some researchers have concluded that a given dose of radiation may be more likely to cause biological effects than previously thought. Some of these studies are listed in the bibliography (Mancuso, Archer) and the BEIR-80 report includes a section analyzing the findings of these and other studies. Scientific opinion differs on the validity of the research methods used and the methods of statistical analysis. The problem is that the expected additional incidence of radiation-caused effects such as cancer is difficult to detect in comparison with the much larger normal incidence. It cannot be shown without question that these effects were more frequent in the exposed study group than in the unexposed group used for comparison, or that the observed effects were caused by radiation. The BEIR committee concluded that claims of higher risk had "no substance."
The NRC staff continually reviews the results of research on radiation risks. With respect to large-scale studies of radiation-induced health effects in human populations exposed to low-level ionizing radiation, the NRC and EPA have recently concluded that there is no one population group available for which such a study could be expected to provide a more meaningful estimate of the low-level radiation risk. This is due, in large part, to the observed natural rate and estimated low incidence of radiation health effects from low doses. However, the results of ongoing studies, such as that on nuclear shipyard workers, will be carefully reviewed and the development of a radiation-worker registry is being considered as a possible data base for future studies.
23. What are the reasons for not lowering the NRC dose limits?
Assuming that the 5-rem-per-year limit is adopted there are three reasons:
a. Health risks are already low.
The estimated health risks associated with current average occupational radiation doses (e.g., 0.5 rem/yr. for 50 years) are comparable to or less than risk levels in other occupational areas considered to be among the safest. If a person were exposed to the maximum of 5 rems per year for 50 years, which virtually never occurs, he or she might incur a risk comparable to the average risks in mining and heavy construction. An occasional 5-rem annual dose might be necessary to allow some jobs to be done without a significant increase in the collective dose. If the dose limits were lowered significantly, the number of people required to complete many jobs would increase. The collective dose would then increase since more individuals would be receiving nonproductive exposure while entering and leaving the work area and preparing for the job. The total number of health effects might go up as the collective dose increased.
b. The current regulations are considered sound.
The regulatory standards for dose limits are based on the recommendations of the Federal Radiation Council. At the time these standards were developed, about 1960, it was considered unlikely that exposure to these levels during a working lifetime would result in clinical evidence of injury or disease different from that occurring in the unexposed population. The scientific data base for the standards consisted primarily of human experience (x-ray exposures to medical practitioners and patients, ingestion of radium by watch dial painters, early effects observed in Japanese atomic bomb survivors, radon exposures of uranium miners, occupational radiation accidents) involving very large doses delivered at high dose rates. The data base also included the results of a large number of animal experiments involving high doses and dose rates. The animal experiments were particularly useful in the evaluation. of genetic effects. The observed effects were related to low-level radiation according to the linear model explained in Question 7. Based on this approach, the regulations in 10 CFR Part 20, "Standards for Protection Against Radiation," also state that licensees should maintain all radiation exposures, and releases of radioactive materials in effluents, as low as is reasonably achievable. More recent scientific reviews of the large body of experimental data, such as the BEIR-80 and the recent EPA guidance, continue to support the view that use of a 5-rem-per-year limit is acceptable in practice. Experience has shown that, under this limit, the average dose to workers is near 0.5 rem/yr. with very few workers consistently approaching the limit.
c. There is little to gain.
Reducing the dose limits, for example, to 0.5 rem/yr. has been analyzed by the NRC staff. An estimated 2.6 million person-rems could be saved from 1980 through the year 2000 by nuclear power plant licensees if compliance with the new limit were achieved by lowering the radiation levels, working times, or both, rather than by using extra workers. It is estimated that something like S 23 billion would be spent toward this purpose. Spending $23 billion to save 2.6 million person-rems would amount to spending $30 to $90 million to prevent each potential radiation-induced premature cancer death. Society considers this cost unacceptably high for individual protection. It should be noted that the annual collective exposure due to natural background radiation in the United States is about 100 million person-rems, about a thousand times greater than the collective dose saved by reducing the exposure limits.
25. How much radiation does the average person who does not work in the nuclear industry receive?
We are all exposed from the moment of conception to ionizing radiation from several sources. Our en-environment, and even the human body, contains naturally occurring radioactive materials that contribute some of the background radiation we receive. Cosmic radiation originating in space and in the sun contributes additional exposure. The use of x-rays and radioactive materials in medicine and dentistry adds considerably to our population exposure.
Table 6 shows estimated average individual exposure in mrems from natural background and other sources.
TABLE 6
U.S. General Population Exposure Estimates (1978)3
Source Average Individual Dose (mrem/yr.)
Natural background (average in U.S.) 100
Release of radioactive material in 5
natural gas, mining, milling, etc.
Medical (whole-body equivalent) 90
Nuclear weapons (primarily fallout) 5-8
Nuclear energy 0.28
Consumer products 0.03
Natural Radon in homes * 100
Total 300
Adapted from a report by the Interagency Task Force on the Health Effects of Ionizing Radiation published by the Department of Health, Education, and Welfare.
Thus, the average individual in the general population receives about 0.3 rem of radiation exposure each year from sources that are a part of our natural and man-made environment. By the age of 20 years, an individual has accumulated about 6 rems. The most likely target for reduction of population exposure is medical uses.
26. Why aren't medical exposures considered as part of a worker's allowed dose?
Equal doses of medical and occupational radiation have equal risks. 7 Medical exposure to radiation should be justified for reasons quite different, however, from those applicable to occupational exposure. A physician prescribing an x-ray should be convinced that the benefit to the patient of the resulting medical information justifies the risk associated with the radiation. Each worker must decide on the acceptance of occupational radiation risk just as each worker must decide on the acceptability of any other occupational hazard.
For another point of view, consider a worker who receives a dose of 2 rems from a series of x-rays or a radioactive medicine in connection with an injury or illness. This dose and the implied risk should be justified on medical grounds. If the worker had also received a dose of 4 rems on the job, the combined dose of 6 rems would not incapacitate the worker. A dose of 6 rems is not especially dangerous and is not large compared to the cumulative lifetime dose. Restricting the worker from additional job exposure during the remainder of the quarter would have no effect one way or the other on the risk from the 2 rems already received from medical exposure. If the individual worker accepts the risks associated with the x-rays on the basis of the medical benefits and the risks associated with job-related exposure on the basis of employment benefits, it would be unfair to restrict the individual from employment in radiation areas for the remainder of the year. Some therapeutic medical doses such as those received from cobalt-60 treatment can range as high as 6000 rems to a small part of the body, spread over a period of several weeks or months.
7 It is likely that a significant portion of reported medical x-ray exposure is to parts of the body only. An exposure of 100 mrem to the whole body is more significant than a 100 mrem chest x-ray.
27. What is meant by internal exposure?
The total radiation dose to the worker is the external dose (measured by the film badge and reported as "whole body dose") plus the dose from internal emitters. The monitoring of the additional internal dose is difficult. Because there is the possibility of internal doses occurring, a good air-monitoring program should be established when warranted.
The uptake of radioactive materials by workers is generally due to breathing contaminated air. Radioactive materials may be present as fine dust or gases in the workplace atmosphere. The surfaces of equipment and workbenches may be contaminated. Radioactive materials may enter the body by being breathed in, taken in with food or drink, or being absorbed through the skin, particularly if the skin is broken.
After entering the body, the radioactive material will migrate to particular organs or particular parts of the body depending on the biochemistry of the material. For example, uranium will tend to deposit in the bones where it will remain for a long time. It is slowly eliminated from the body, mostly by way of the kidneys. Radium will also tend to deposit in the bones. Radioactive iodine will seek out the thyroid glands (located in the neck) and deposit there.
The dose from these internal emitters cannot be measured either by the film badge or by other ordinary dosimeters carried by the worker. This means that the internal radiation dose must be separately monitored using other detection methods.
Internal exposure can be estimated by measuring the radiation emitted from the body or by measuring the radioactive materials contained in biological samples such as urine or feces. Dose estimates can also be made if one knows how much radioactive material is in the air and the length of time during which the air was breathed.
28. How are the limits for internal exposure set?
The limits in 32 IAC Part 340 are for the combination of exposures from both internal and external sources. It is the responsibility of the Licensee to determine occupational uptakes and calculate the expected dose from an uptake. If both the internal and external doses calculated exceed 10% of the regulatory limit, then the doses must be summed and the workers permanent dose history changed to include the internal exposure.
In general, the quantities of isotopes used do not require routine monitoring for internal contamination. The exception is for I-125 and I-131. Anyone working with more than 1 millicurie at a time must have a thyroid bioassay performed. Bioassays for other isotopes may be required when an unusually large quantity of material is used, or in the case of an accident.
29. Is the dose a person received from Internal exposure added to that received from external exposure?
Yes, if both the internal and external doses exceed 10% of the limits.
30. How is a worker's external radiation dose determined?
A worker may wear three types of radiation-measuring devices. A self-reading pocket dosimeter records the exposure to incident radiation and can be read out immediately upon finishing a job involving external exposure to radiation. A film badge or TLD badge records radiation dose, either by the amount of darkening of the film or by storing energy in the TLD crystal. Both these devices require processing to determine the dose but are considered more reliable than the pocket dosimeter. A worker's official report of dose received is normally based on film or TLD badge readings, which provide a cumulative total and are more accurate.
31. What are my options if I decide not to accept the risks associated with occupational radiation exposure?
If the risks from exposure to radiation that may be expected to occur during your work are unacceptable to you, you could request a transfer to a job that does not involve exposure to radiation. However, the risks associated with exposure to radiation that workers, on the average, actually receive are considered acceptable, compared to other occupational risks, by virtually all the scientific groups that have studied them. Your employer is probably not obligated to guarantee you a transfer if you decide not to accept an assignment requiring exposure to radiation.
You also have the option of seeking other employment in a nonradiation occupation. However, the studies that have compared occupational risks in the nuclear industry to those in other job areas indicate that nuclear work is relatively safe. Thus, you will not necessarily find significantly lower risks in another job.
A third option would be to practice the most effective work procedures so as to keep your exposure ALARA. Be aware that reducing time of exposure, maintaining distance from radiation sources, and using shielding can all lower your exposure. Plan radiation jobs carefully to increase efficiency while in the radiation area. Learn the most effective methods of using protective clothing to avoid contamination. Discuss your job with the radiation protection personnel who can suggest additional ways to reduce your exposure.
32 Where can I get additional information on radiation risk?
The Office of Radiation Safety is always happy to answer any of your questions, and if necessary direct you to other sources of information such as:
The Illinois Department of Nuclear Safety
U. S. Nuclear Regulatory Commission
Department of Health and Human Services
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