Sleepiness of day workers and watchkeepers on board at high seas: a cross-sectional study

OBJECTIVES: To estimate the prevalence of sleepiness on duty among day workers and watchkeepers on board. DESIGN: Cross-sectional survey in a maritime field study. SETTING: 10 shipping companies with container vessels under German management. PARTICIPANTS: The whole crew (75 day workers and 123 watchkeepers) during 18 voyages on 18 different container ships. OUTCOME MEASURES: Sleepiness on duty and efficiency of sleep using pupillometry (in a cross-shift design) and the SenseWear armband activity monitor. RESULTS: The watchkeepers showed significantly shorter sleep periods than day workers (5.5 hours vs 5.8 hours). The average efficiency of sleep was 69.6% and significantly lower among watchkeepers (OR 0.48; 95% CI 0.26 to 0.88). 396 pupillometric examinations were carried out and revealed 88 study members (22.2%) with a pupillary unrest index (rPUI) in a range characterised as ‘unfit for duty’ and 110 seafarers (27.8%) categorised as ‘particular attention required’. The average rPUI was similar between day workers and watchkeepers. The Epworth Sleepiness Scale revealed recent daytime sleepiness in 70 seafarers, which was similarly often stated by day workers and watchkeepers. Based on the Stanford Sleepiness Scale (SSS), a measurable cross-shift increase in the SSS value during the examined shift was observed, especially among watchkeepers. The amount of time already spent on the vessel at the time of the present examination was significantly associated with the rPUI (p=0.009). CONCLUSION: Sleep periods of both the day workers and the watchkeepers aboard vessels were alarmingly short and sleep efficiency was low. Sleepiness on duty is similarly prevalent among day workers and watchkeepers and seems to depend partly on the cumulative working period on the vessels. Preventive measures need to be taken by the shipping industry to counteract fatigue (eg, by enabling sufficient rest and sleep times).