282 



TEMPERATURE AND HUMIDITY 



radiate to adjacent skin areas and therefore 

 not to the environment. Thus, although 

 the entire surface area of the human body 

 can be calculated from the height-weight 

 formula of DuBois, only a portion of this 

 area can be completely effective in losing 

 heat by radiation. It is obvious that the 

 bodily pose of the individual is of the greatest 

 importance in considering the radiation 

 area, because when a person is curled up 

 with the knees drawn against the chest, the 

 effective area will be much less than in the 

 fully extended "spread eagle" configuration. 

 By means of partitional calorimetry, 

 Winslow (44) and his colleagues found a 

 value of 71-75 percent for a man sitting in a 

 chair in a semi-rechning position. Investi- 

 gators at the Russell Sage Institute of 

 Pathology (20) found by two methods a 

 value of 78 percent for a man in a "mummy" 

 position. It can therefore be assumed that 

 for normal extended positions of the body the 

 effective radiating area will be somewhere 

 between 70 and 85 percent of the area figured 

 by the DuBois formula. 



Representative values for the emissivities 

 of a number of different materials are given 

 in Table VI. 



It is possible to state an equation for 

 computing the heat transfer by radiation. 

 The formula for transfer between nude man 

 and the environment, assuming the emissiv- 

 ity and temperature of the environment can 

 be measured, is as follows: 



(6) Hr = 1.37 X 10-11 {Ts^ - Tc") 



X ^ X A X / X €, kg. cal./hr. 



where Ts = average skin temperature 

 (°C + 273), Tc = average radiant environ- 

 mental temperature (+273), t = seconds in 

 one hour, A = DuBois surface area, / = 

 ratio of effective radiating surface to the 

 DuBois surface area (0.78 for nude man 

 lying in anatomical position), and e = emis- 

 sivity of the environment. 



The average skin temperature can be 

 obtained by measuring the skin temperature 



of various areas over the body surface and 

 weighting the readings according to the 

 proportion of the DuBois (14) body area 

 represented. If a man is clothed, the 

 "radiant" surface temperature of both skin 

 and clothing may likewise be determined by 

 weighting temperatures determined by a 

 radiometer. The difficulties associated with 

 surface temperature measurements are criti- 

 cally discussed by Murhn (29). 



The average radiant temperature of the 

 indoor environment is measured most easily 

 by pointing a calibrated radiometer to 

 many points over the entire solid angle of 

 four radians and making an appropriate 

 average. There is as yet no instrument 

 available which will give this average in a 

 single reading. 



The factor / is dependent upon the amount 

 of clothing and the position of the individual ; 

 it has been worked out only for the nude 

 man in one or two instances. As men- 

 tioned above, the emissivity of the environ- 

 ment is difficult to measure. It is generally 

 safe to assume a value of about 0.95 for 

 most environments, but in cases of doubt, 

 where poHshed surfaces are present, it is 

 better to make actual temperature measure- 

 ments of the surfaces in the environment 

 when practical. There is no instrument at 

 present which will give in a single measure- 

 ment the emissivity of the environment. 



In summary, the determination of the 

 radiation exchange between a man and his 

 environment requires six measurements: 



a. Physiological 



1. Skin or surface temperature 



2. Effective surface area 



3. Reflecting power of the skin and 



clothing 



b. Environmental 



1. Average radiant temperature (infra- 



red) 



2. Emissivity of the environment 



3. Intensity of radiant sources 



