Occupational Exposure to Radiation

Exposure to ionizing radiation occurs in many occupations. Artificial sources of radiation are commonly used in the manufacturing and service industries, in areas of defense, in research institutions, and in universities, as well as in the nuclear power industry.

Some workers are also exposed to natural sources of radiation in such circumstances that a measure of supervision and protection is required. This is particularly true of exposure to radon in mines and in ordinary premises throughout areas where radon levels are high.

With the relatively high dose rates experienced in air travel due to elevated levels of cosmic rays at flying altitudes, some consider that supervision is also required for air crew, although it is less clear to what extent their exposures can readily be reduced.

Many people who are exposed to radiation in their work wear personal monitoring devices (or dosimeters) such as a small photographic film or some thermo-luminescent material in a special holder.

There is also increasing use of electronic devices for this purpose. These register the radiation incident on the body from external sources and yield an estimate of the dose received by the wearer.

For airborne activity in the workplace, whether of artificial or natural origin, it is usually best to sample the air that the worker breathes, measure it, and then estimate the internal dose.

In some cases, it may be possible to measure activity in excreta and infer the dose or indeed measure the activity in the body directly with sensitive detectors. The objective always is to get the best possible estimate of dose.

Artificial Sources Artificial Sources

There are about 800 000 workers in the nuclear industry worldwide, and over 2 million workers exposed in medical facilities. UNSCEAR (United Nations Scientific Committee on the Effects of Atomic Radiation) has compiled data on doses received by these workers and others such as industrial radiographers.

The collective dose to nuclear industry workers is about 1400 man Sv (Sievert, unit of radiation absorption) while that for medical radiation workers is about 800 man Sv.

There are fewer workers in industrial uses of radiation, therefore the collective dose is lower at about 400 man Sv. However, these workers get the highest individual doses in some countries.

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The average dose overall to occupationally exposed workers from artificial sources is less than 1 mSv in a year. The average in the nuclear industry tends to be a little higher than this, while the average for medical staff is slightly less.

With the exception of mining, average doses from most types of occupational exposure from artificial sources, including the nuclear industry, are now below about 2 mSv in a year.

Doses in the health professions, medical, dental and veterinary are generally very low, but there are still matters of concern.

Some clinical procedures with diagnostic radiology require the physician to be close to the patient and at risk of appreciable exposure. X ray equipment and procedures in veterinary practices are frequently inadequate.

Occupational Exposure to Radiation

Natural Sources

Occupational exposure to enhanced natural sources of radiation occurs mainly in mines, buildings and aircraft. Almost 4 million coal miners are monitored for radiation exposure.

Fewer people (about a million worldwide) work in mines other than coal mines and in the processing of ores with levels of natural activity appreciably above average. The doses incurred are, nevertheless, monitored routinely.

Radon levels and doses are low in coal mines because the ventilation is usually good. Few if any miners exceed 15 mSv in a year. The state of ventilation in metal and other mines is not always as satisfactory, so the average dose is much higher and a fraction of the workforce does exceed this dose.

About one-fifth of the people considered to be occupationally exposed to enhanced natural radiation work in shops, offices, schools, and other premises in radon-prone areas. Within these areas, the average dose is appreciable.

The average dose for such workers is almost 5 mSv per year higher than for the other groups of occupationally exposed workers.

However, it should be remembered that this group is unusual in that its members are identified, precisely because they receive high doses, rather than because they have the same occupation.

Radon levels vary markedly from day to day because of the way buildings are heated and ventilated, so short measurements of radon in air may be misleading. The best remedy for high radon levels is the same as in houses, reduced air pressure under the floor.

Doses to aircrew from cosmic rays depend on the routes flown and the amount of flying time. On average, the annual dose is around 3 mSv, but it could be twice as much for long flights continually at high altitudes. By the nature of the radiation and the operations, such doses are unavoidable.

Average Radiation Exposure to Public and Workers

Generally, public exposure to radiation from natural sources dominates the total exposure. UNSCEAR estimated the average annual effective dose to an individual at about 3 mSv.

On average, the annual dose from natural sources is 2.4 mSv and two thirds of it comes from radioactive substances in the air we breathe, the food we eat and the water we drink.

The main source of exposure from artificial sources is radiation used in medicine, with an individual average annual effective dose of 0.62 mSv. Medical radiological exposure varies by region, country and health-care system.

UNSCEAR has estimated the average annual effective dose from medical applications of radiation in industrialized countries at 1.9 mSv and in non- industrialized countries at 0.32 mSv. However, these values might vary considerably (e.g. in the United States with 3 mSv or in Kenya with only 0.05 mSv).

In summary, the average dose overall to occupationally exposed workers from artificial sources is less than 1 mSv in a year. About one-fifth of the people considered to be occupationally exposed to enhanced natural radiation work in shops, offices, schools, and other premises in radon-prone areas.

Doses in the health professions, medical, dental and veterinary are generally very low, but there are still matters of concern.

Exposure to ionizing radiation occurs in many occupations. Artificial sources of radiation are commonly used in the manufacturing and service industries etc.

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Some workers are also exposed to natural sources of radiation in such circumstances that a measure of supervision and protection is required.

This is particularly true of exposure to radon in mines and in ordinary premises throughout areas where radon levels are high. Generally, public exposure to radiation from natural sources dominates the total exposure.

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Benadine Nonye

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