23rd February 2012

Shift work in the offshore vessel fleet: Circadian rhythms and cognitive performance

Jakob Hønborg Hansen

Thesis for the degree of Philosophiae DoctorNorwegian University of Science and TechnologyFaculty of Natural Sciences and TechnologyDepartment of Biology

Shift work

• Statistics Norway: 761,000 (34%) employees aged between 15-67 work outside “normal” working hours [1].

• Round the clock operations are essential in the offshore sector. → Thus, shift work is essential.

Shift work causes:

• Sleep disturbances.

• Sleep loss and drowsiness.

• Diminished cognitive performance.

• Higher accident rates.

• Certain health disorders [2-8] .

Types of shifts used on offshore vessels

• 6-h shifts (6-h on, 6-h off, 6-h on, 6-h off)

• 12-h shifts (12-h on, 12-h off)

• 8-8-4-4-h shifts (8-h on, 8-h off, 4-h on, 4-h off)

Aim of thesis

1) Effects of working 12-h, 6-h and 8-8-4-4-h shifts in the offshore vessel fleet (Papers I & II).

2) The adaptation to working 12-h night shifts (Papers III & IV).

3) Physical exercise and cognitive performance (Paper V).

Problem assignment

1. There is a need to investigate how workers on offshore vessels are affected by working 12-h, 6-h and 8-8-4-4-h shifts, since these are currently in use in the offshore vessel fleet.

2. Circadian phase misalignment is a matter of safety. It is of vital importance to investigate the physiological and cognitive adaptation to 12-h night shifts.

3. Physical exercise can reduce cognitive performance impairments. It is important to investigate this as a possible natural countermeasure for combating sleepiness and cognitive impairments in night-shift workers.

Hypothesis

1. In offshore vessel workers the 6-h shift schedule is inferior to both the 12-h shift schedule and the 8-8-4-4-h shift schedule.

2. Offshore vessel workers on the 12-h night shift adapt to the working schedule, but the adaptation is slower compared to workers in other sectors of the offshore industry.

3. Physical exercise improves cognitive performance at night.

Effects of working 12-h, 6-h and 8-8-4-4-h shifts in the offshore vessel fleet(Papers I & II)

Paper IHansen JH & Holmen IM. Sleep disturbances among offshore fleet workers. A questionnaire based survey. Int Marit Health. 2011;62(2):123-130.

Aim• To investigate differences between offshore fleet shift workers on 6-h and 12-h shifts.

• Sleep disturbances onboard and at home.• Causes of sleep disturbances.• Safety. • Regional differences.

Hypothesis• The 6-h workers suffers from more sleep disturbances.• This is perceived as a safety risk.• The causes of sleep problems are largely identical. • There are regional differences.

Sleep disturbances

Sleep problems at home

Causes of sleep disturbances

Conclusion of paper I• 6-hour shift workers suffer more from sleep disturbances than 12-h shift workers.

• The sleep problems only occur at sea.

• Safety was not perceived as being compromised.

• Noise and the shift-work itself is worse among 6-hour shift workers.

• There are regional differences in most parameters.

Paper IIKongsvik T, Hansen JH, Størkersen K. The possible impact of different watch-keeping regimes at sea on sleep, fatigue, and safety. Accepted in ESREL 2011 annual conference (European Safety and Reliability Association).

AimTo investigate differences between the 6-h shift schedule, and the 8-8-4-4-h shift schedule. • Objective sleep quality.• Subjective sleep quality.• Cognitive function.• Fatigue.• Safety perceptions.• Accident/near miss involvement.

Research questionAre there differences between different watch keeping schedules regarding sleep, cognitive function, fatigue, safety perceptions, and accident/near miss involvement?

Sleep length and sleep efficiency

6-6 schedule: average 1.7 sleep episodes per day on the tour.

8-8-4-4 schedule: average 1.3 sleep episodes per day.

Sleep episodes

Fatigue, sleep and rest

1 = totally disagree 5 = totally agree

Conclusion of paper II

• The offshore vessel workers on the 8-8-4-4-h schedule had:• Better sleep efficiency.• More continuous sleep. • More sufficient sleep than the 6-h workers .

• No differences in cognitive function.

• No differences regarding safety perceptions and accident/near-miss involvement.

The adaptation to working 12-h night shifts (Papers III & IV)

Paper IIIHansen JH, Geving IH, Reinertsen RE. Adaptation rate of 6-sulfatoxymelatonin and cognitive performance in offshore fleet shift workers: a field study. Int Arch Occup Environ Health. 2010;83:607-615.

AimTo determine:• The adaptation of 6-sulfatoxymelatonin. • Subjective sleep quality.• Objective sleep quality.• Cognitive performance.

Hypothesis• There will be an adaptation of 6-sulfatoxymelatonin. The adaptation is smaller than in other offshore workers.• Improvements in subjective and objective sleep quality.• Improved cognitive performance.

Conclusion of paper III

• The offshore fleet workers adapted to working 12-h night shifts. The acrophase of 6-sulfatoxymelatonin was phase delayed by 4.04 h, with a daily rate of adaptation of 50 min. The adaptation is slower compared to other offshore workers due to exposure to lower light intensities.

• Subjective sleep quality improved to some extent in the course of the 7 days. There were no significant improvements in objective sleep quality.

• Cognitive performance improved significantly after 7 days on the shift.

Paper IVHansen JH, Geving IH, Reinertsen RE. Offshore fleet workers and the circadian adaptation of core body temperature, blood pressure and heart rate to 12-h shifts: A field study. Int J Occup Saf Ergon. 2010;16(4):487-496.

AimTo investigate the adaptation of:• Core body temperature.• Blood pressure. • Heart rate. • Subjective sleep quality.

Hypothesis• Core body temperature, blood pressure and heart rate will increase. • The increases are predicted to be lower than in other shift workers.• Subjective sleep quality will improve.

Core body temperature

Conclusion of paper IV• Core body temperature increased by 0.6 °C in the night workers and between the night and day workers, after 7 days on the shift.

• Blood pressure and heart rate showed no changes.

• Subjective sleep quality showed inconclusive results in the night workers.

• The day workers did not experience any changes in subjective sleep quality.

Paper VHansen JH, Geving IH, Reinertsen RE. Core body temperature and cognitive performance after treadmill running in simulated night conditions. Submitted December 2010 to Aviation, Space, and Environmental Medicine (ASEM).

AimTo investigate if:• Physical exercise improves cognitive performance and subjective sleepiness. • Core body temperature or cortisol secretion is related to these improvements.

Hypothesis• Physical exercise at night improves cognitive performance and subjective sleepiness. • Cognitive performance is related to core body temperature, but not cortisol secretion.

= exercise condition - - - - = non-exercise condition

Conclusion of paper V

• Cognitive function and subjective sleepiness improved after exercise. These improvements are related to increases in core body temperature.

• There were no relation between the secretion of cortisol and cognitive performance.

• Exercise at night can be used as a countermeasure for fighting certain aspects of cognitive performance decrements and reducing subjective sleepiness.

General conclusions• 12-h shifts and 8-8-4-4-h shifts are preferable to 6-h shifts.

• Offshore vessel workers on 12-h night shifts adapt to the shift schedule. This adaptation is slower compared to other branches of the offshore industry, primarily due to exposure to lower light

intensities.

• Physical exercise can counteract sleepiness and improve cognitive performance at night.

References[1] Andersen A, Køber T, Rønning E. Skift og turnus – omfang og mønster; Oslo: Statistisk Sentralbyrå, 2008. Rapport 2008/38.

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[3] Davey CP. Physical exertion and mental performance. Ergonomics 1973;16:595-599.

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[6] Gillberg M, Åkerstedt T. Sleep loss and performance: no “safe” duration of a monotonoustask. Physiol Behav 1998;64:599-604.

[7] Folkard S, Tucker P. Shift work, safety and productivity. Occup Med (Lond) 2003;53:95-101.

[8] Lie J, Gulliksen E, Pettersen R, Skogstad M. Arbeidstid og helse. Et systematisklitteraturstudie. Oslo: Statens Arbeidsmiljøinstitutt (STAMI), 2008. Report No. 9-21.