A. R. \V. WILSON 



relatively uniform rate throughout the lifetime of the individual. Accord- 

 ingly, the quantities of these materials have been calculated to give a dose 

 rate to the critical organ of not more than 0-3 REM per week, although 

 over a lifetime this could amount to a total of some 750 REM. 



(c) The build-up of radio-active material on laboratory surfaces to a level which is 

 likely to lead to appreciable transfer into the bodies of persons working in the 

 laboratory 

 Dunster^ has derived permissible contamination levels for laboratory 



surfaces based on ^^Sr in the case of |8 emitters and '^^Pu and 226Ra in the 



Table 1. Assumptions used in deriving tabulation of maximum amounts of activity 

 recommended for use under specified conditions* 



1. White Area: Open Room 



(a) Day-to-day transfer .-—Average daily transfer into the body assumed to be not greater than 

 0- 1 per cent of total activity in use, on the basis that the laboratory practice and housekeepmg 

 are equal to the standards of a well-run chemical laboratory. 



(b) Spill or explosion ingestionlinhalation .-—Ingestion of 0- 1 of total activity is not sufficient to 

 cause a lifetime dose to the critical organ exceeding 25 REM or alternatively a weekly dose 

 of 0-3 REM in the cases of plutonium and thorium. Activity inhaled following a spill or 

 explosion is not sufficient to gi\e a lifetime dose to the critical organ exceeding 25 REM or 

 alternatively a weekly dose of 0-3 REM in the cases of plutonium and thorium under 

 following circumstances : — 



(i) all activity is airborne. • u r 



[ii) active material is uniformly distributed by the spill or explosion in a sphere of 

 radius equal to the distance between the explosion point and the head of the worker. 

 {Hi) sphere of active material drifts past the worker with a velocity determined by the 

 air change rate in the laboratory (20 changes/hr). 



(c) Contamination build-up .-—Daily spread of activity is assumed to be one per cent of the 

 total in use and routine cleaning procedures result in the removal of 90 per cent of this^ 

 25-vear build-up in the case of all P emitters is not to give levels exceeding 4 X 10"* (xC/cm^ 

 over a total floor area of 50 m- and in the cases of ^sspu and --^Ra levels not exceeding 

 10-5 [iC/cm- over the same area. -^'Pu and "sRa level is modified for other a emitters in 

 the ratio of the respective maximum permissible daily intakes. 



2. Blue Area: Open Room 



{a) Day-to-day transfer: — Special measures adopted in the handling of radio-active materials 

 {e.g., the wearing of gloves and the monitoring of laboratory air) result in a reduction of the 

 transfer to 10 per cent of the white area transfer. 



(i) Spill or explosion ingestionlinhalation :— Ingestion of 0-01 of total activity is not sufficient 

 to gi\e a lifetime dose to the critical organ exceeding 25 REM or alternatively a weekly 

 dose of 0-3 REM. Activity inhaled following spill or explosion is not sufficient to give a 

 lifetime dose to the critical organ exceeding 25 REM or alternatively a weekly dose of 

 0-3 REM under the conditions of l{b) except that only 0- 1 of the material is assumed to 

 become airborne. ■ n 



(f) Contamination build-up :—So limit is applied since routine monitoring is carried out in all 

 blue areas. However, the limits set by 2(a) and (A) result in the contamination hazard being 

 not more than 10^ times the white area contamination hazard. 



3. Blue Area : Fume Hood 



Fume hood containment is assumed to reduce both transfer and spill or explosion hazards 

 to one per cent of the blue area open-room case. No contamination build-up limit applied. 



4. Red Area : Open Room and Fume Hood 



Definition of red area recognizes hazardous levels possible at tirnes, hence all red area 

 limits have been placed at 10 times the corresponding blue area limits. 



5. Red Area : Glove Boxes or Sealed Cells 



Upper limit is set by fire and explosion hazard and each case must be considered 

 individuallv. 



• It is here assumed that the radid-ai live material is in tlic form of a tine dry powder which is the foriH most 

 likely to be transferred into the body b\- inhalation. 



11 149 



