Yes, studies have shown that long or unusual working shifts have a negative impact on worker safety. One study found that visits to the emergency room from workplace injuries increased nearly threefold outside of regular working hours. Between 6am and 4pm, it was fairly constant at 2 per 200,000. However, outside of this normal shift, the rate jumped to over 5 per 200,000 between the hours of 8pm and 3am, peaking at nearly 7 between midnight and 2am. The increase applied to manual, non-manual, and mixed jobs. The study states that this sharp increase was likely due to worker fatigue and less supervision during off hours.