54 



RADIATION BIOLOGY 



Altlit)ut»;h this exposure toleranee mi{i;ht seem to supply an unnecessary 

 factor of safety, it provides for some unusual skin sensiti\ities bordering 

 on the pathologic. Experience in hospitals and in inchistria' applications 

 indicates, for example, that some adult face skins are more sensitive to 

 ultraviolet irritation than the face skin of the average infant . The Amer- 

 ican Medical Association has not had occasion to specify a corresponding 

 sui^erythemal exposure for '29()7 A ultraviolet, but its unit exposure for 

 a minimum perceptible erythema on average untanned skin is 300 nw- 

 min/cm-, as indicated in Fig. 2-76. 



It should be noted here that there is no theory or evidence that the 

 erj'thema produced by 2537 A energy differs at all from that produced by 

 29G7 A except that the former is more superficial and transient. Expo- 

 sures to comparable erythemas which result in skin peeling after 2957 A 

 produce only scaling after 2537 A. This difference in effect, shown in the 

 erythemal-action curve of Fig. 2-1, may be due entirely to the slightly 

 deeper penetration of 29G7 A into the skin (see Chap. 13, this volume). 



Useful germicidal intensities of 2537 A ultraviolet range from 5 to 6000 

 Mw/cm-, and the corresponding suberythemal exposure times are from 

 less than 40 min to 2 sec. The intensity of ultraviolet reflected from sur- 

 faces and walls of a minimum reflectance of 5-10 per cent may range from 

 5 /iw downward. From this it is obvious that there is always a problem 

 of face and eye protection in practical applications of ultraviolet energy. 



Table 2-2 extrapolates the American INIedical Association's permissible 

 exposure through practical ranges of time and intensity. 



Table 2-2. M.\ximum Permissible Daily F^cposures 



"Permissible intensity in hospital infant wanis; onc-liftieth or one one-hundredth 

 that recommended for hospital air disinfection. 



* Exposures (time times intensity) of 3.6 juw-hr/cm'. 



'Intensity recommended for hospital upper-air disinfection; tolerated only 10-30 

 min if on the faces of personnel. 



'' Exposures (time times intensity) of 216 /j\v-min/cm^. 



FACE AND EYE PROTECTION AND TREATMENT 



Commercially available sun glasses and face shields designed to cover 

 the eyes from the sides and the ears completely provide adequate protec- 

 tion. Hands and arms may be protected by plastic or rubber or very 



