clude that due to radioactive contaminants deposited in the skin. In connection with the four types of hazard enumerated above it is important to bear in mind that the permissible exposure as quoted applies under conditions where only one hazard exists. In the handling of radioisotopes, all four hazards exist together, and this may reduce the permissible exposure to each. Simple summation of the ionization contributions at any point in the body from the four enumerated causes is assumed.2 In particular, the total irradiation of any part of the body (with the exceptions noted above), should not exceed 300 mrep/week. It is advisable to keep well below the quoted permissible exposures whenever mixed exposures may occur, because of the increased difficulty of registering such exposures accurately. 4. Principle Underlying Protective Measures The fundamental purposes of protective measures in the handling of radioisotopes are: 1. To prevent ingestion, inhalation, interstitial, or other modes of entry into the body. 2. To reduce the amounts of external irradiation to permissible levels. The first requirement is fulfilled by good housekeeping and work habits, and by operation in a laboratory properly equipped for the handling of isotopes, including protective covering, manipulative devices, suitable ventilation, and waste disposal facilities. The second requirement, maintenance of satisfactory levels of external radiation, is governed by procedures such as those contained in the National Bureau of Standards Handbook 23, "Radium Protection," which should be available to all persons working with radioisotopes. Special requirements arise when isotopes with beta activity, essentially free from gamma activity, are used. Laboratories that specialize in the use of a few isotopes should become familiar in detail with the published data on the metabolism and estimated maximum permissible concentration values applicable to these cases. Where many 2 Note that the contributions from internal deposition or skin contamination will be effective 24 hr/day, and 7 days/week. Contributions from external sources are limited to the normal workweek (48 hours). 3 A more detailed discussion of permissible limits of exposure will be found in the report of the Subcommittee on Permissible Dose from External Sources, now in preparation. types of isotopes are in use, the following values form a provisional guide to maximum permissible contamination: (1) For atmospheric contamination: 10-9 μc/cm 3 (2) For water contamination: 10-μc/cm3 II. Personnel 1. Selection and Instruction of Personnel Persons who are neat and careful are preferred workers with radioisotopes. A rigid physical examination should be made of all prospective workers. Careful inspection of the hands, and evaluation of possible previous exposure to radiation, are recommended. All individuals employed in radiation work shall be informed in detail of all known dangers involved. They shall be instructed regarding local rules and regulations for protection, and should be expected to observe them in all details. It is particularly important that all users of radioisotopes should be considered as potential full-time users. 2. Effects of Radiation Effects of external radiation are adequately described in the National Bureau of Standards Handbooks 23 and 41. When the active materials are deposited in the body, the effects depend upon the site of deposition, the physical halflife, and the biological half-life, which is determined by the elimination rate. The bone-seekers (for example, strontium) will produce effects similar to those found in radium poisoning. Other materials may produce changes in liver or kidney function, and occasionally in other organs. An essential feature of all the effects is that they may not appear until the dangerous material has resided in the body for many years, and irreparable latent damage may have been produced. There usually are no definite clinical symptoms which can be relied upon to guard against possible impending injury. 3. Blood Count A complete blood count shall be made by a qualified hematologist before any individual begins work involving the handling of radioactive materials. Counts on two successive days at a stated hour are desirable. No one should be em ployed who shows pertinent abnormalities in the blood count. Blood counts should be made at regular intervals (normally 3 months) during employment, with more attention given to the trend of successive counts and especially of the differential count than to absolute values. It should not be considered that overexposure of the individual will be detected by changes in blood count. Poor protection techniques may be detected by blood count findings before permanent injury to the individual occurs.5 4. Physical Examinations (a) General A thorough medical examination should be made of each individual potentially exposed to significant amounts of radiation before employment, and annually thereafter. An examination for possible radioactivity, by a person with special knowledge and equipment, should be given each individual, and form a part of the annual physical examination, whenever the exposure potential includes significant internal deposition. More frequent examinations are warranted when the exposure potential is high. The nature of such tests will depend upon the particular isotopes to which the individual may have been exposed. Sufficiently sensitive tests for the deposition of all relevant isotopes may not exist. (b) Urinalysis and Other Tests An analysis of radioactivity of the urine is a desired procedure. Normal urine contains radiopotassium in amounts which may mask the added radioisotopes for which tests are made. Either potassium should be separated from the sample and the residual activity measured, or when the possible exposure is restricted to one isotope, this should be chemically separated from the urine. Examination of the feces may be required when the predominant elimination is by feces. Special tests for specific isotopes are in order when they exist (e. g., radioiodine may be estimated in the thyroid gland in terms of the emitted gamma radiation measured by a Geiger counter or ionization chamber). Where exposure 4 A single exposure of 25 r can apparently escape detection by standard blood counting techniques. 5 A more detailed discussion on blood counts will be found in National Bureau of Standards Handbook 41, Medical X-ray Protection up to Two Million Volts. to radioisotope dust or spray is a possibility, it may be desirable to test the activity of a nasal smear, or of the sputum. 5. Personal Cleanliness Radioactive isotopes must be treated like other poisonous substances. Extreme personal cleanliness in the laboratory is, therefore, desired. The material must not be spilled or scattered, and must not come in contact with the hands or clothing to any appreciable extent. At the end of each work period, the hands shall be carefully washed. No edibles of any kind, including chewing gum, candy, or beverages, shall be brought into the laboratories, nor shall they be touched before removing all washable traces of radioisotopes from the hands. The use of cigarettes or application of cosmetics in the laboratory may result in transference of activity to the lips. Radioisotopes burned on the cigarette may be drawn into the lungs. The hands should be tested frequently with a Geiger counter or other instruments of suitable sensitivity to determine whether contamination exists. Immediate steps to remove contamination shall be taken when found. 6. Housekeeping Neatness in the laboratory is a prime requisite for elimination of the spread of contamination. The work area should be free from equipment and materials not required for the experiment at hand, and equipment used should be decontaminated and stored in a controlled location after use. 7. Supervision The supervisor of a work group or the leader of a laboratory group has the responsibility for seeing that the radiation work under his guidance is performed in a safe manner. The supervisor is required to see that the established rules regarding food handling, checks of personnel activity, waste disposal, etc., are maintained. The objective is the education of each and every worker to follow these necessary procedures for his own protection and the protection of others. In a radioisotope laboratory, skill in radiation protection is as necessary as skill in chemical or biological manipulations. Persons failing to develop such skills should be advised to transfer to other occupations. III. Laboratory Design and Equipment 1. General Working Conditions Successful work with radioisotopes other than in true tracer amounts requires the use of laboratories and equipment specially designed for the purpose. No work should be undertaken in these rooms other than that concerned with the application of radioisotopes. 2. Floors The floors shall have smooth and continuous surfaces, as far as possible, such as stainless steel, painted concrete, or linoleum. Absorbent floors, for example, wood, should be avoided. Asphalt tile and similar materials are permissible, provided that the laboratory supervisor is aware of the hazards of accumulation of radioisotopes in the cracks. The ease of replacement of sections of tile floor may compensate for the hazard of crack contamination. Floors should be cleaned daily by wet mopping, or by the use of moist compound. Dry sweeping may lead to an active dust hazard. 3. Walls, Ceiling, and Woodwork Walls, ceiling, and woodwork shall be finished with a nonporous washable surface, which may be cleaned to remove accumulation of radioactivity. Projecting ledges, hanging lamps, etc., which may accumulate dust should be avoided. 4. Ventilation All laboratory operations with more than low-level activity should be conducted in hoods which will be provided with forced ventilation sufficient to maintain the activity content of the room air below 10-9 μc/cm3 at any place at any time. The linear velocity of air flow should be in the range of 100 to 150 feet/minute. Specially hazardous operations (e. g., handling long-lived bone-seeking isotopes in injection or inhalation studies on animals) should be conducted by personnel wearing suitable respirators or supplied-air masks. Hoods with individual filter systems for the exhaust air are preferred. Multiple hood systems are dangerous because reverse air currents may occur. |