Fatigue in industrial workers under thermal stress on extended shift lengths.

A field investigation to examine the fatigue levels in industrial workers working extended (10, 12 and 12.5 h) shifts under significant levels of thermal stress was conducted on 45 male underground miners. Studies were conducted both before and after a major change to the working-in-heat protocol used at the operation. Prior to the change, shortened (6 h) shifts had been used when thermal conditions exceeded certain values. This reduced shift length was removed and replaced with other protocols. Heart rates were continuously monitored, and a cycle ergometer was also used to assess cardiovascular fatigue over the shift. Average heart rates, as well as highest 10 and 30 min averages, and heart rate durations within various bands were analysed. No worker reported heat illness during the study. Results showed that removing the shortened shift did not increase the fatigue levels. Workers did experience fatigue, but this occurred in the first half of the shift. Evidence was found that these workers practised self-pacing.