Operator performance and signs of sleepiness during day and night work in a simulated thermal power plant

The objective was to assess operator performance, subjective and objective sleepiness in a simulated thermal power plant under realistic production conditions. Twelve experienced operators participated in two conditions, a night shift (2300-0700 h) and a day shift (0800-1600 h), in a balanced design. The work tasks were constructed to get maximum realism. The simulator logged the state of the processes. This information was used to calculate indicators of operator performance in 2-h blocks: deviation from pre-planned production of heat and electricity, the net profit made, the time to acknowledge warning signals, the time to stop and restart a coal mill and the number of errors made. Subjective sleepiness was rated every 20 min. Electrophysiological (EEG and EOG) signals were recorded continuously. In spite of higher sleepiness during the night shift, as indicated by subjective ratings and to some extent by electrophysiological recordings, operator performance was not negatively affected. In fact, performance tended to be worse during the day. It is concluded that the performance of experienced operators may not deteriorate during night shifts in control room work of the present type, probably due to lower workload during the night, lack of monotony and to the processes being relatively inert and forgiving to minor operator errors.