NASA, in preparation for the Apollo missions, concluded a person with a body temperature of 98.6º F makes (on average) 80 mistakes, per hour. With a body temperature of 100.0º F, a person can make up to 250 mistakes, per hour.
Why did subjects make more mistakes with just a 2º shift? The heat! A temperature delta around the skull is more influential to homeostasis—the bodies ability to maintain biological functions—than a temperature delta around any other part of the body; an overheating head means an overheating body.
Between 3 - 5,000 American construction workers in 2012 died on the job due to mistakes that are easily avoided with proper cognition and focus. Protocols, no matter how comprehensive or explicit, do not override the faults human beings are biologically susceptible to.
Study NASA CR-1205-1.