Extended duration and irregularly planned overnight shifts are becoming frequent features of current working time arrangements. However, there is great concern about the detrimental effect that these shifts are likely to have on the sleep, performance and fatigue levels of workers. To date, the empirical evidence regarding the effects of extended and irregular overnight shifts is sparse and workers have rarely been followed up longer term to assess possible changes over time. Because these types of overnight shifts are being introduced into transport settings such as aviation and shipping where safe and productive operations are paramount, there is a real imperative to examine and trial workplace-based methods aimed at counteracting night shift related fatigue and performance deficits. Taking short duration naps on the nightshift at work is one potential countermeasure that has shown promise in the laboratory but has yet to be examined in any real-world setting under conditions of extended duration or irregular night work. This thesis takes up these issues in a series of four empirical workplace-based studies.
The impact of the introduction of regularly planned 12 h day and overnight shifts was examined on three occasions via questionnaire in a group of aircraft maintenance engineers, once before the change, and twice after the change from 8 h shifts. The results showed that high levels of acute fatigue on the 12 h night shifts and high chronic fatigue levels were common, and were strongly associated with poor overall job performance, poor safety of job performance, and longer recovery times, effects that persisted over time. Of major concern was the finding that over half of the engineers reported having nodded off while driving home from their extended overnight shifts. The impact of irregularly planned 8 h overnight shifts worked by cargo handlers in a shipping container terminal was also examined via self-report questionnaire. The findings revealed significant detrimental impacts on sleep, fatigue levels and performance at work. High fatigue levels were strongly associated with poor self-rated performance output and safety of performance at work on the overnight shifts.
The primary focus of this thesis was to evaluate the effect of a scheduled 20 min nap opportunity taken in these two fully operational workplaces during the night shift on sleep, performance and alertness. Sleep was achieved by 50 to 59% of workers. Speed of performance in 24 male aircraft maintenance engineers on a vigilance task was significantly faster at the end of a 12 h overnight shift that had contained sleep during the nap compared to the control condition. There was no such effect of the nap on the performance of 22 cargo handlers working impromptu 8 h shifts in a shipping container terminal. However, the duration of sleep obtained by the 8 h workers was shorter in comparison and was likely to have been undermined by the high noise levels around the nap facility and time pressures related to the organisation of work. Actigraphy data recorded from all subjects showed that subsequent daytime sleep was not disrupted by the night shift nap opportunity. Overall, the most interesting findings were that simply being tired and presented with a sleep opportunity during the night shift did not guarantee either sleep, or recovery but that sleep, as opposed to rest, was necessary for the benefits to performance to be fully realised.
These findings have shown for the first time that management of fatigue associated with extended duration night work can be achieved in some instances by the use of a short duration nap taken in the workplace on the night shift. However, operationalizing in-situ napping on the night shift has a range of organisational influences that must be considered for the potential of such a strategy to be fully harnessed.
| Identifer | oai:union.ndltd.org:ADTP/217424 |
| Date | January 2005 |
| Creators | Purnell, Melissa T., n/a |
| Publisher | University of Otago. Dunedin School of Medicine |
| Source Sets | Australiasian Digital Theses Program |
| Language | English |
| Detected Language | English |
| Rights | http://policy01.otago.ac.nz/policies/FMPro?-db=policies.fm&-format=viewpolicy.html&-lay=viewpolicy&-sortfield=Title&Type=Academic&-recid=33025&-find), Copyright Melissa T. Purnell |
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