The effects of heat stress on operator perceived workload in tracking

Abstract

Eight male unacclimatized subjects were selected for the present investigation. The subjects were all in excellent health and ranged in age between 25 and 35 years. Subjects performed one-dimensional horizontal compensatory tracking, the Critical Instability Tracking Task (CITT), in each of eight environmental conditions for an hour. Two levels of ambient temperature were used: 22°C (72°F) and 35°C (95°F). Two levels of relative humidity were used: 45% RH and 80% RH. The resulting Wet-bulb Globe Temperatures were 18°C (64°F) WBGT, 21°C (70°F) WBGT, 29°C (85°F) WBGT, and 34°C (93°F) WBGT. Two levels of tracking difficulty were used: easy ()λlow = 1.0 and λhigh = 2.0) and moderate (λlow = 1.0 and λhigh = 5.0). Prior research has demonstrated that both ambient temperature and tracking difficulty affected significantly tracking performance (root-mean-square error) and perceived workload (SWAT rating). However, in this study, humidity did not affect either measure significantly. This might be attributable to the upper bound of humidity (80% RH) used in this research. Therefore, research needs to be done above 80% RH to examine the effects of humidity in further detail. Results also indicated that the Subjective Workload Assessment Technique (SWAT) can be used as a good indicator of the actual changes in mental workload on tracking in heat. Finally, results showed that tracking performance decrement occurred at a lower temperature (29°C (85°F) WBGT) than did the perception of significant mental workload on tracking (which occurred at 34°C (93°F) W8GT).