Circadian rhythm
Fatigue on board is still a major factor of accidents which lead to casualties, damage and pollution. Studies show that most accidents happen during the night especially around 4 am due to the "Circadian rhythm" of "humans". Studies like Project Horizon have recently been done to analyse which factors cause this fatigue. The lack of sleep and quality of the sleep are two of the main issues. The lack of sleep is due to the long hours that the workers (especially the Officers) have to do (work weeks of 70 hours +). After that there is the quality of their sleep which is affected by a variety of factors. There will be the quality of the food on board, the vibrations due to the engine and waves, the noise of repair or works or engine, only naps (not sleeping eight hours in a single run but two or three naps a day) because of the watch system and secondary jobs. Stress on board especially when arriving in port when all hands have to be on deck whatever the time.