Combined effects of occupational noise exposure and shiftwork on performance tasks in a seafaring population

This study was undertaken to complement a cross-sectional survey of the combined effects of selfreported workplace stressors. Data were collected from seafarers on board support vessels for the North Sea oilrigs as part of a project on offshore fatigue. These data could also be used specifically to address whether there were any cognitive effects associated with working in loud noise at night that were different to working in loud noise during the day, low noise at night or low noise during the day. The participants were 62 male workers from 3 different vessels. Their mean age was 40.3 years. Individuals were from a range of different jobs onboard the vessels. There were two between-subjects factors (day/night shift and noise exposure) and one within-subjects factor (test session). Workers were asked to complete a battery of computer tests both before (Pre-shift) and after (Post-shift) their shift on one day. Four tests were presented using laptop computers. These tests were visual analogue mood scales, a simple variable fore-period reaction time, and categoric search and focused attention choice reaction time tasks. The mood scales were presented at the beginning and end of the testing session. Occupational noise exposure (Leq) was measured over a two-day period using a dosimeter. Workers were categorised into day/night workers by their shift pattern. Regression analyses distinguishing noise exposure, day/night shift and their interaction were performed on the data from each test session and the change score between the start and end of the shift. Noise exposure was associated with increased alertness but also with slower reaction times. Those working night shifts showed a large drop in alertness over the course of work and became slower at tasks requiring more difficult responses. There were also a limited number of interactions between noise and shift, such as more lapses of attention (very long response times) but fewer incorrect responses in the noise/night-work condition. The findings suggest that these techniques may provide valuable information about the possible combined effects of occupational stressors in situ. The present analyses are based only on a small number of night workers and further consideration of effects of potential confounding influences must also be undertaken