Page:Operation Crossroads 1946.pdf/143

 Exception (a) Underwater body, readings statistically averaged not above 0.02r beta gamma combined and with no single localized area in excess of 0.1r beta gamma combined

Exception (b) salt water systems having external readings ninety-four (94) per cent of which are not above 0.001r gamma, five (5) per cent not above 0.005r (gamma) and, one (1) per cent not above 0.01r gamma.

The letter also stated:

"All of the ships involved (target vessels not included) have low radiation intensities and small amounts of contaminating materials. They present no danger from external radiation. Any danger to personnel which may exist involves the introduction of contaminating toxic materials into the body.... Considering the relatively small quantities of toxic material present in any one ship and the great amount of gross material with which it is mixed (marine growth, scale, rust) and the quantities of this gross material necessary to gain access to the body in order to provide physical injury due to radioactive effects it is NOT LIKELY that personnel engaged in routine operations or maintenance of these vessels will suffer injury. It is CERTAIN they will not suffer injury if the precautions directed are followed, and the established clearance procedures complied with. The Bureau of Medicine and Surgery has established certain tolerance limits on the basis of recommendations made by an advisory board of experts in this field of toxicology. These are in conformity with nationally accepted standards for safety in regard to external radiation and to radioactive hazards within the body."

On 27 November at a conference on radiological safety convened by BuShips in Washington, D.C., a University of California scientist speaking to the question of dangers from scraping CROSSROADS nontarget ships took much the same position. He stated that much authoritative information indicated the insoluble form of plutonium used in nuclear weapons was not absorbed in the digestive tract or the lungs unless quantities as large as a gram were present. he argued that the health hazards from long-lived fission products, such as strontium and cesium, were far greater than from plutonium. The amount of such fission products would be on the order of 50 millicuries in many tons of scrap. This quantity of radioactive material was equivalent to the amount of radiation found in ordinary rock. Therefore, he was willing to state positively that there was absolutely no possibility of physical injury from the amounts of radioactive material present on the nontarget ships (Reference C.9.187, pp. 112 and 113).

On 18 December, results from tests at the University of California indicated that decay rates of gamma emitters were much greater than had been realized. This led to some revision of the clearance instructions, and a re-estimation that all nontarget ships would receive final clearance by 15 March 1947 (Reference C.9.185, pp. 60 and 61).

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