272 Applied Biophysics 



reduced to 10"^ r per second is much too cautious. i\ssuming 

 a working week of 35 hours, and 48 working weeks per year, 

 in conformity with the International and British Recommenda- 

 tions, Muller's figure corresponds to 0.06 r per year, which is 

 sHghtly less than the natural radiation intensity. Hence, if the 

 whole human race were exposed to an additional intensity of 

 10"^ r per .second, the mutation rate would not be doubled. 



The regulations of the Berufsgenossenschaft fiir Gesund- 

 heitsdienst und W'ohlfahrtspflege recommend that, for the genital 

 organs, the daily dose should not exceed 0.025 r. This is one- 

 tenth of the ordinary tolerance dose accepted by the German 

 X-ray Society. Jaeger and Zimmer ^^ considered that, as the 

 number of workers using ionizing radiations in 1941 was still a 

 relatively small proportion of the total population, even this 

 value of 0.025 r per day represented a very cautious attitude. 



Risks by Inhalation or Ingestion 



We now turn to the consideration of other classes of radia- 

 tion workers, namely, those who may sufifer injury from radio- 

 active materials which have been inhaled or ingested. As regards 

 radon, the British X-ray and Radium Protection Committee ^^ 

 recommend that "the radon of the air in laboratory, factory, 

 workshop or other working quarters should not exceed a con- 

 centration of 10"^^ curie per liter." As regards radium in the 

 body, the Committee recommend that if, after the person has 

 remained away from work for 48 hours, "radon then be found 

 in a concentration of even 10"^^ curie per liter, it is presumptive 

 evidence of radium in the body and the operator should at once 

 discontinue such work." In the National Bureau of Standards 

 Handbook H.27 on the Safe Handling of Luniinoits Compounds, 

 much lower tolerance levels are advised, namely, "the radon 

 concentration in the atmosphere of workrooms shall not exceed 

 10"^^ curie per liter," and "no one shall be engaged as a dial 

 painter who shows more than 0.1 microgram of deposited 

 radium as revealed by the expired air test." It is stated that 

 the latter figure corresponds to 10"^- curie of radon per liter 



