Performance on a simple response time task: Is sleep or work more important for miners?
Introduction
Shiftwork, particularly night work, is associated with an increased risk for incident and accident (Akerstedt, 1995, Dinges, 1995). Specific features of shiftwork patterns that are thought to contribute to increased risk include extended shifts, night work and consecutive shifts. For example, the risk of a fatal accident increases significantly beyond 9 h at work (Nachreiner et al., 2000), and accident risk after 12 h on shift is twice that seen after 8 h (Folkard and Tucker, 2003). Night shift, particularly the end of night shift, is also reported to be a high-risk time (Axelsson et al., 1998, Folkard and Tucker, 2003, Rosa and Bonnet, 1993) and is associated with a range of performance impairments (Folkard, 1997, Jay et al., 2006, Monk et al., 1997, Muller et al., 2008, Rollinson et al., 2003). Finally, the number of consecutive shifts worked is also a risk factor for accidents and incidents (Folkard and Tucker, 2003). Twelve-hour shift rosters, particularly those involving night shifts contain each of these elements – long hours, night work and strings of shifts.
A major advantage of 12-h shifts is that they compress the working week into fewer days, thus providing more rest days away from work. In addition, the rest days are often grouped together to provide blocks of time off. While extended blocks of days off are attractive for employees (Smith et al., 1998), there may be negative repercussions for performance and safety when the number of consecutive shifts is increased. The number and timing of rest days is an important component of the shift pattern, particularly in 12-h rosters (Tucker et al., 1999) and insufficient and/or infrequent recovery days may cause impairment due to cumulative sleep loss.
A 12-h break provides for approximately 6 h of sleep depending on the start time of the break (Roach et al., 2003). Current knowledge suggests that 6 h of sleep per night is a threshold below which performance becomes significantly impaired due to cumulative sleep restriction (Belenky et al., 2003, Van Dongen et al., 2003). Analysis of accident and error data confirm this hypothesis such that sleep loss associated with work hours is indeed predictive of impaired performance (Dorrian et al., 2004a, Dorrian et al., 2004b, Dorrian et al., 2008, Lockley et al., 2004). Thus, in any investigation of work hours and waking function, sleep history is an essential component.
Each of the work factors discussed, long shifts, nights, and consecutive shifts, is associated with circadian misalignment, extended wakefulness, inadequate sleep, or a combination thereof. The current study therefore looked at the impact of both work- and sleep-related factors on an objective measure of performance in operators working different 12-h shift patterns. It was expected that both work- and sleep-related factors would be associated with performance changes in this population and that roster type would mediate performance due to different distribution of rest days.
Section snippets
Participants
The study was conducted in two phases in 2005 and 2007. Initially, a total of 111 participants across four different roster patterns were recruited to the study – 54 in phase 1 and 57 in phase 2. Individual datasets were not included in the analysis if individuals did not complete all aspects of the data collection, if they worked a pattern significantly different to one of the main rosters (sick/annual leave, overtime etc) or if they withdrew from the study. The dataset used in the current
Work-related factors
As illustrated in Fig. 1, the 7 × 4 roster was associated with lowest RRT scores (indicating highest performance impairment), followed by the 14 × 7, then the 4 × 4. Analyses indicated that these differences were not significant (F2,34.1 = 2.69, p = 0.08). There was a main effect of test time (F3,402.6 = 8.25, p < .001) on RRT. Pairwise comparisons indicated that RRT was significantly lower during tests conducted at the end of night shifts compared to any other shift/timing combination indicating poorer
Discussion
The study examined performance on a psychomotor vigilance task in three different rosters in the same mine site. As expected, response times were slower at the end of night shifts compared to any other testing time. However, there were no significant differences in response times across roster. Sleep history was a significant predictor of response time in this group: Tests conducted with less than 6 h of prior sleep produced slower response times than those conducted following more than 7 h of
Acknowledgements
The authors would like to acknowledge the participating organisation and individuals for their contribution to the study.
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