PROTECTION from radiation cannot be complete, for we are convinced that even the radiation from the necessary potassium in our bodies produces random biological changes. However, we can hope to avoid unacceptable risks to the person exposed and to the genetic constitution of the race. We aim to avoid effects that a physician would deem unacceptable, and to incur no more than a negligible probability of severe injury.The probability of leukemia and carcinoma and of nonspecific injuries that shorten the average lifetime does rise to an unacceptable level, we believe, after exposures that produce no observable acute effect. It is these late sequelae and the induction of gene mutations that determines our radiation hygiene. The requirement: "nothing that a physician would deem unacceptable" 1 is a concession to the general sentiment that even a little radiation is harmful. This is an inevitable paraphrase of what has become a scientific truism, namely, that every bit of radiant energy absorbed by a living system surely affects it in some way.The International Commission on Radiological Protection (ICRP) 1958 recommendation sets the maximum permissible dose (MPD) for occupational exposure at N -18 X 5 rems in gonads, bloodforming organs, and lenses of eyes. In this formula, N is the age, and it is presumed that no occupational exposure begins before age 18. The permissible rate of accumulation is 3 rems per quarter.Emergency exposure is permitted up to 12 rems (except for women of reproductive age), but if the accumulation exceeds the formula, the excess shall be made up. An accidental exposure less than 25 rems shall be figured into the recorded accumulation. (Excess above the N -18 X 5 rem limit on one occasion may be ignored.) If the accidental exposure exceeds 25 rems, the matter shall be referred to competent medical authorities, who will presumably consider the serious aspects of the person's exposure and tell him that he may go back to work.The permissible exposure of skin to very soft radiation and exposure limited to hands and feet is calculated from the whole body MPD by factors of 6 and 15, respectively, for annual dose, but smaller factors for quarterly dose. For internal irradiation the permissible levels are calculated from the limit of 0.3 rems per week, except that the dose for gonads and lenses shall not exceed 1.5 rems peryear.
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