Criteria for physiological limits for work in heat

¹ Human Sciences Laboratory and Mathematical Statistical Division, Transvaal and Orange Free State Chamber of Mines, Johannesburg, South Africa

New physiological criteria are put forward for setting the limits for men at work in hot conditions. They are based upon the fact that the curves relating rectal temperatures to conductances and rectal temperatures to sweat rates have two components. One is where the increases in the sweat rates and conductances, with rise in rectal temperature, are relatively large, i.e., there is a "sensitive" range of control; the second is where the curves of sweat rates and conductances against rectal temperatures reach asymptotes, i.e., become "saturated." The upper limit of the sensitive range is a rectal temperature of 100.5 F (38.1 C), and the saturated range begins at rectal temperatures of 102.5 F (39.4 C). These concepts explain the "easy," "difficult," or "excessive" ranges of conditions of the Fort Knox and Human Sciences Laboratory studies. The great advantage of these criteria over others proposed is that the extent of the physiological strain on the workmen can be assessed, directly and simply, by a measurement of oral or rectal temperatures during the shift, and from these results limits for work can be set for work at specific hot jobs.

Submitted on March 20, 1964