Young adults averaging 23 years of age were tested to design work and rest schedules for hot job conditions according to the cumulative circulatory strain exerted by the combined stress induced by work, walking with and without carrying objects and heat. Work and rest periods for walking and walking combined with carrying were established for 30, 40, 60 and 75 percent maximum oxygen consumption, with the work being carried out at neutral, warm and humid, and hot and dry ambient conditions. The rest periods following each work session were kept the same as during the corresponding work conditions, that is, warm, hot or neutral. The cumulative muscular strain exerted by muscular work and heat, in terms of the increase in heart rate was used to establish the length of the work periods, and the sum of the heart rates was expressed in terms of percent maximum oxygen consumption. An efficient rotation between workers was applied to establish the work periods. The pattern recorded for heart rate and the rectal temperature of the test subjects demonstrated that the test method was satisfactory for hot and dry working conditions, regardless of the conditions prevailing during the resting period. On the contrary, for the warm and humid conditions, the procedure was satisfactory only when resting occurred in neutral ambient conditions. The author concludes that the cumulative stresses of work and heat can be used to establish work and rest schedules for hot jobs.
Proceedings of a NIOSH Workshop on Recommended Heat Stress Standards, September 17-19, 1979, Cincinnati, Ohio