Shift work is associated with both sleepiness and reduced performance. The aim of this study was to examine cognitive performance, sleepiness, and sleep quality among petrochemical control room shift workers. Sixty shift workers participated in this study. Cognitive performance was evaluated using a number of objective tests, including continuous performance test, n-back test, and simple reaction time test; sleepiness was measured using the subjective Karolinska Sleepiness Scale (KSS); and sleep quality was assessed using the Pittsburgh Sleep Quality Index (PSQI) questionnaire. ANCOVA, t-test, and repeated-measures ANOVA were applied for statistical analyses, and the significance level was set at p < 0.05. All variables related to cognitive performance, except for omission error, significantly decreased at the end of both day and night shifts (p < 0.0001). There were also significant differences between the day and night shifts in terms of the variables of omission error (p < 0.027) and commission error (p < 0.036). A significant difference was also observed between daily and nightly trends of sleepiness (p < 0.0001) so that sleepiness was higher for the night shift. Participants had low sleep quality on both day and night shifts, and there were significant differences between the day and night shifts in terms of subjective sleep quality and quantity (p < 0.01). Long working hours per shift result in fatigue, irregularities in the circadian rhythm and the cycle of sleep, induced cognitive performance decline at the end of both day and night shifts, and increased sleepiness in night shift. It, thus, seems necessary to take ergonomic measures such as planning for more appropriate shift work and reducing working hours.

Cognitive demand and mental workload assessment are essential for the optimal interaction of human-machine systems. The aim of this study was to investigate the cognitive demands and mental workload as well as the relationship between them among the mining control room operators.

Night shift work is associated with many problems such as sleep deprivation, sleepiness, decreased cognitive performance, increased human errors, and fatigue. This study set out to measure cognitive performance, melatonin rhythms, and sleep after different consecutive night shifts (7 vs. 4) among control room operators (CORs). The participants included 60 CORs with a mean age of 30.2 years (standard deviation, 2.0) from a petrochemical complex located in Southern Iran. Cognitive performance was assessed using the n-back task and continuous performance test. To evaluate melatonin, saliva was collected and tested by enzyme-linked immunosorbent assay. To assess sleep and sleepiness, the Pittsburgh Sleep Quality Index and Karolinska Sleepiness Scale were used, respectively. Individuals who worked 7 consecutive night shifts had a significantly better cognitive performance and sleep quality than those who worked 4 consecutive night shifts. However, salivary melatonin profile and sleepiness trend were not affected by shift type. The main duty of CORs working night shifts at the studied industry included managing safety-critical processes through complex displays; a responsibility that demands good cognitive performance and alertness. It is suggested that an appropriate number of consecutive night shifts in a rotating shift system should be planned with the ultimate aim of improving CROs performance/alertness and enhancing safety.

A two-shift work schedule with different rotations is common among firefighters in Iranian petrochemical companies. This study compared salivary melatonin and sleepiness on the last night before turning to day shift at 19:00, 23:00, 3:00, and 7:00 among petrochemical firefighters (PFFs) working seven and four consecutive night shifts. Sixty four PFFs working in the petrochemical industry were selected. To measure melatonin, saliva samples were taken, whereas the KSS index was used to assess sleepiness. Chi-square and independent samples t-test were carried out to analyze the data, and generalized linear model (GLM) was employed to determine the effect of confounding factors such as lighting and caffeine. The levels of melatonin at 3:00 and 7:00, and the overall changes during the shift in the two shift patterns under the study were different (P < 0.05). Sleepiness was significantly different only at 3:00 in the two studied shift patterns, while the effects of lighting and caffeine on melatonin changes were not significant (P > 0.05). It seems that a slow shift rotation is better because it reduces the secretion of melatonin (hence reducing sleepiness during the night) and changes the peak of melatonin secretion to the daytime, which is a sign of adaptation.