304 



TEMPEIL\TURE AND HUMIDITY 



work is approximately equal to walking at 

 three miles per hour with a 20-pound pack. 

 These data show that at air temperatures 

 above body temperature, with low humidity, 

 the effect of clothing variation is not con- 



TABLE XIV 



Dehydration Stress Related to Clothing 



IN Subjects Working Under Hot Conditions 



(Total Metabolism, 279 kg.cal./hr.) 



cooling at the 29.4°C (85°F) condition and 

 the dominance of evaporative cooling at 

 43.3°C (110°F). 



In Table XV are summarized data from 

 Yaglou (47), relating clothing, comfort 

 sensations, and body temperatures, for in- 

 dividuals under sedentary conditions. As 

 noted earlier, work of the order of three 

 times this resting level of heat production 

 reduces the comfort level for the nude sub- 

 ject by 12°C (18°F). Hence, for partially 

 stripped working subjects, we may approxi- 

 mate the comfort point at work by allowing 

 a decrease of 4°C (7.2°F) from the level of 

 sedentary comfort for each increase of 100 

 percent in heat production over the basal 

 level. 



The Clo Concept and Unit of Clothing 

 Insulation 



Herrington (27) has discussed the joint 

 influence of clothing and level of heat pro- 

 duction on thermal adaptation, and gives 

 particular mention to the "clo" concept of 



TABLE XV 

 Effect of Variation in Clothing on the Temperature of Thermal Comfort at Rest 



(from Yaglou, 47) 



spicuous at low air velocities. However, at 

 moderately hot temperatures with high hu- 

 midity, the dehydration effect of added 

 clothing is conspicuous. The thermal analy- 

 sis of this differential effect is complicated, 

 but, in general, the difference depends upon 

 the importance of radiation and convection 



clothing insulation. The widespread use of 

 partitional methods of estimating heat and 

 cold stress from subjects and models has 

 created a need for a unit of heat insulation 

 which would have practical meaning for non- 

 technical groups. Such a unit should be 

 convertible into the BTU/sq.ft./°F used by 



