According to a recent study that matched occupational illness and injury

...to shift scheduling for emergency medical services (EMS) workers, the risk of injury was 60% greater for employees that worked shifts greater than 16 hours and less than or equal to 24 hours in duration, compared to shifts greater than 8 hours and less than or equal to 12 hours in duration.

Source: "An observational study of shift length, crew familiarity, and occupational injury and illness in emergency medical services," Occupational & Environmental Medicine, abstract only, September 14, 2015, http://oem.bmj.com/content/early/2015/08/26/oemed-2015-102966.short?g=w_oem_ahead_tab