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Permissible Levels of Exposure

Today's human risks of irradiation, if we do not take into account nuclear accidents and nuclear terrorism, can be represented accordingly with its contribution like as is shown below:

Dose Determination: The Total Effective Dose Equivalent (TEDE) is calculated by adding the dose determined from the badge dosimeter (external deep dose equivalent) to that of determined from urine and thyroid bioassay procedures (internal committed effective dose equivalent).

It is generally accepted that there is no safe level of exposure to ionizing radiation, and the search for quantifying such a safe level is in vain. Different permissible levels were accepted for human body exposure based on a series of value judgments, scientific estimations and experimental data. These levels are varying slightly depending on country and mainly decreasing dramatically with time and gaining of human experience.

Human experience with ionizing radiation had been recorded for more than fifty years prior to the nuclear age, the early history of handling radioactive material having been fraught with tragedy. The discoverer of the X-ray, W. K. Roentgen, died of bone cancer in 1923, and the two pioneers in its medical use, Madame Marie Curie and her daughter, Irene, both died of plastic anaemia at ages 67 and 59 respectively. At that time, bone marrow studies were rarely done, and it was difficult, using blood alone, to distinguish aplastic anaemia from leukemia. Both diseases are known to be radiation-related. Stories of early radiologists who had to have fingers or arms amputated abound. There were major epidemics among radiation workers, such as that among the women who painted the radium dials of watches to make them glow in the dark. Finally, there were the horrifying nuclear blasts in Hiroshima and Nagasaki.

The painful period of growth in understanding the harmful effects of ionizing radiation on the human body was marked by periodic lowering of the level of radiation exposures permitted to workers in radiation-related occupations. For example, permissible occupational exposure to ionizing radiation in the United States was set at 52 roentgen (X-ray) per year in 1925 [1], 36 roentgen per year in 1934 [2], 15 rem per year in 1949 [3] and 5 to 12 rem per year from 1959 (depending on average per year over age 18) to the present [4].

In 1952 the International Commission on Radiological Protection (ICRP) issued its recommendations for limiting human exposure to external sources of radiation. The organization accepted the standard agreed upon by nuclear physicists from the USA, Canada and the UK after the Second World War [5]. In 1959 it issued its recommendations for limiting human exposure to internal sources of radiation. The early ICRP dose limits per year were: 5 rem to the whole body, gonads or active bone marrow; 30 rem to bone, skin or thyroid; 75 rem to hands, arms, feet or legs; and 15 rem to all other body parts. These standards applied only to "man-made" sources, other than medical exposures for diagnostic or therapeutic purposes of benefit to the patient exposed.
ICRP Publication 2, in 1959, recommended no more than 5 rem per year external or internal exposure to the whole body due to inhalation, ingestion or absorption of radioactive chemicals into the body.
In terms of the amount of whole body dose received in a chest X-ray (about 0.03 rem at the present time), this recommendation for workers allowed the equivalent of 400 chest X-rays in some years with a 170 (present-day) chest X-ray average (external and internal) dose a year. Prior to 1970 some X-ray machines used in mass chest X-ray programmes gave as high as 3 rem per chest X-ray.
When one looks at dose to bone marrow, the permissible levels are even more troubling. By 1970 the average bone marrow dose for a chest X-ray was 0.001 to 0.006 rem averaging about 0.005 rem. In terms of dose to bone marrow, the ICRP radiation recommendation for workers permits up to the equivalent bone marrow dose of 1,000 chest X-rays per year.
ICRP recommended that members of the general public should receive no more than one-tenth of the occupational exposure or 0.5 rem per year, the equivalent bone marrow dose of about 100 present-day chest X-rays per year. The bone marrow dose is important for estimating the likelihood of causing bone cancer, leukemia, aplastic Anaheim or other blood disorders. Medical X-rays are less penetrating of bone than of soft tissue, making them valuable for `picturing' the bones. For this reason comparisons between radiation exposures of nuclear workers and medical X-ray exposures are more appropriately based on the bone marrow dose of each than on dose to soft tissue.
These radiation exposure recommendations stayed essentially the same until 1978, when in ICRP Publication 26 a recommendation was made to raise the levels of radiation permitted to humans from man-made sources of radiation (excluding that for medical purposes). For "internal consistency" of the recommendations there was some valid argument for scaling the standards for particular organ exposure in proportion to whole body exposure recommendations - but scaling down as well as up would have accomplished this. For example, the ICRP reasoned that if the whole body could receive 5 rem per year, the active bone marrow should not be limited to 5 rem per year. This was used as a reason for increasing the permitted bone marrow dose from 5 rem to 42 rem with apparently little regard for the increased damage to bones and blood-producing organs.
ICRP Publication 26 also reiterates the need to allow human exposure in order to enjoy the "economic and social benefits" of the nuclear industries.
Some national regulatory agencies, such as the Atomic Energy Control Board of Canada (Since May 31, 2000 the Canadian Nuclear Safety Commission), implemented ICRP Publication 26 by increasing allowable radium levels in drinking water, thus reducing the cleanup cost for the uranium mining companies.

1. Recommended by pioneer researchers A. Mutscheller and R. M. Sievert in 1925. Recommended for international use by the forerunner of the International Commission on Radiological Protection (ICRP) in 1934. Used in most countries until 1950.

2. Recommended by the US National Commission on Radiological Protection (NCRP), 17 March 1934.

3. Recommended by the US NCRP, 7 March 1949 and hy ICRP, July 1950, for total body exposure.

4. Recommended by ICRP, April 1956 and US NCRP, 8 January 1957, for total body exposure. This allows for 5 rem per year combined dose from sources external to the body, ingested or inhaled sources. This standard is used in most countries of the world today.

5. British, Canadian and American nuclear physicists met in Chalk River, Canada in September 1949 and at Buckland House, UK in August 1950 to agree on radiation-dose levels for workers. Their recommendations were accepted by ICRP.

Maximum permissible exposure

In the USA government standards for radiation protection are established by the National Council on Radiation Protection and Measurement (NCRP) and its international counterpart, the International Commission on Radiological Protection (ICRP). Both of these organizations offer recommendations for the maximum permissible dose (MPD) of radiation to which people should be exposed, and those recommendations are generally adopted by various government regulatory agencies as the maximum limits permitted by law. Current MPD limits are shown below:
Maximum Permissible Dose (MPD)



General Public

 Annual MPD

1 mSv

1 mSv

Radiation Workers

Annual MPD

50 mSv

20 mSv

Cumulative MPD

10 mSv x age


MPD During Pregnancy

5 mSv

2 mSv


In making their maximum permissible dose recommendations, both NCRP and ICRP divide the population into two groups: members of the general public, and "radiation workers" who are exposed to radiation through their occupation. Government standards establish limits for occupational exposure that are 20 to 50 times greater than those established for the general public. The rationale is that "radiation workers" presumably accept the increased risk by informed consent as a tradeoff in exchange for the benefits of employment.

Note that in addition to its annual MPD for occupationally exposed radiation workers, the NCRP recommends a cumulative lifetime limit (in mSv) equal to 10 times a worker's age. So, for instance, a pilot who retires at age 60 should not be exposed to more than 600 mSv over his entire flying career. Assuming that career lasts 30 years, average annual exposure should not exceed 20 mSv.

Both organizations recommend drastically reduced limits for occupationally exposed workers during pregnancy.

Dose limits established by the U.S. Nuclear Regulatory Commission (NRC) for work with radioisotopes
Dose Limits per Year for work with radioisotopes
Radiation Workers: Dose
Total Effective Dose Equivalent (TEDE)
5 rem
Dose Equivalent to the Eye
15 rem
Shallow Dose Equivalent to skin, extremities
50 rem
TEDE to any other individual organ
50 rem
TEDE to embryo/fetus of declared pregnant woman
0.5 rem
10% of worker limit
Members of the Public
0.1 rem
Probable Health Effects resulting from Exposure to Ionizing Radiation
Dose, rem (whole body)
Immediate Health Effects Delayed Effects
1,000 or more
Immediate death. "Frying of the brain"
600 - 1,000
Weakness, nausea, vomiting and diarrhoea followed by apparent improvement. After several days: fever, diarrhoea, blood discharge from the bowels, haemorrhage of the larynx, trachea, bronchi or lungs, vomiting of blood and blood in the urine.
Death in about 10 days. Autopsy shows destruction of hematopoietic tissues, including bone marrow, lymph nodes and spleen; swelling and degeneration of epithelial cells of the intestines, genital organs and endocrine glands.
250 - 600
Nausea, vomiting, diarrhoea, epilation (loss of hair), weakness, malaise, vomiting of blood, bloody discharge from the bowels or kidneys, nose bleeding, bleeding from gums and genitals, subcutaneous bleeding, fever, inflammation of the pharynx and stomach, and menstrual abnormalities. Marked destruction of bone marrow, lymph nodes and spleen causes decrease in blood cells especially granulocytes and thrombocytes.
Radiation-induced atrophy of the endocrine glands including the pituitary, thyroid and adrenal glands.
From the third to fifth week after exposure, death is closely correlated with degree of leukocytopenia. More than 50% die in this time period.
Survivors experience keloids, ophthalmological disorders, blood dyscrasis, malignant tumours, and psychoneurological disturbances.
150 - 250
Nausea and vomiting on the first day. Diarrhoea and probable skin burns. Apparent improvement for about two weeks thereafter. Foetal or embryonic death if pregnant.
Symptoms of malaise as indicated above. Persons in poor health prior to exposure, or those who develop a serious infection, may not survive.
The healthy adult recovers to somewhat normal health in about three months. He or she may have permanent health damage, may develop cancer or benign tumours, and will probably have a shortened lifespan. Genetic and teratogenic effects.
50 - 150
Acute radiation sickness and burns are less severe than at the higher exposure dose. Spontaneous abortion or stillbirth.
Tissue damage effects are less severe. Reduction in lymphocytes and neutrophils leaves the individual temporarily very vulnerable to infection. There may be genetic damage to offspring, benign or malignant tumours, premature ageing and shortened lifespan. Genetic and teratogenic effects.
10 - 50
Most persons experience little or no immediate reaction. Sensitive individuals may experience radiation sickness.
Transient effects in lymphocytes and neutrophils. Premature ageing, genetic effects and some risk of tumours.
0 - 10
Premature ageing, mild mutations in offspring, some risk of excess tumours. Genetic and teratogenic effects.