Time-of-day and days-on-shift predict increased fatigue over two-week offshore day-shifts

The purpose of this study was to investigate the accumulation of fatigue over a two-week offshore period. In particular, the effects of (1) time-of-day and days-on-shift as well as (2) acute and chronic sleep loss on the rate at which fatigue accumulates were investigated.

42 day-shift offshore workers were examined. Fatigue was measured using pre- and post-shift scores on the Karolinska Sleepiness Scale (KSS). Total sleep time was measured using actigraphy (Motionwatch8, Camntech). Data was analyzed using a linear mixed model analyses.

Average sleep loss per night was 92 min (95%CI: 89.6-94.0; p < .001). Mean cumulative sleep loss across the study was 21:20hrs (SD = 08:10hrs) over the 14 days. Chronic sleep loss was significantly related to a modest increase in sleepiness (KSS) across the shift (95%CI: 0.01-0.17; p = .020) and in post-shift scores (95%CI:.07-0.19; p < .001). Time-of-day (95%CI: 0.63 to -0.01; p = .042) and days-on-shift (95%CI: 0.03-0.08; p < .001) as well as their interaction (95%CI: 0.08 to -0.00; p = .027) influenced the rate at which fatigue accumulated over a two-week offshore period.

Pre- and post-shift fatigue accumulate in different ways over the two-week offshore period. The accumulation of post-shift fatigue scores was positively related to successive days-on-shift and chronic sleep loss. Our results suggest that prolonging offshore periods will likely result in elevated fatigue risk. Accumulating fatigue and sleep loss over two-week offshore periods should be considered in fatigue risk management plans and systems.