In my investigation work, I often get asked to provide performance parameters of people in accidents. One of these parameters is reaction time. The question often goes like this “Exactly how long would it have taken the operator to react to a warning alarm if the last sleep he obtained was 17 hours ago?”
That’s a really good question, but it’s a hard one to answer. Science does not work that way. We can only provide estimates that are (normally) based on the average person. There are just too many variables that can’t be accounted for when predicting exactly how any one specific person will behave in any one specific situation. The best we can do is speak in generalities.
When it comes to reaction time and sleep, it gets even harder to predict. Without any data about things like baseline mental processing speeds, hand-eye coordination, age, baseline reaction times and even limitations of mechanics behind warning systems, it’s impossible to provide an answer like “It would have taken the operator 1.5 seconds to react to the warning.”
Research findings do, however, provide us with relative estimates. Here are a few reaction time findings that I regularly refer to in my work:
- At between 17 and 18.5 hours of continuous wakefulness, many aspect of performance involved with driving (like hand eye-coordination) are at levels similar to what you would find in a person with a Blood Alcohol Concentration (BAC) of 0.05%[1,2]. At 21 hours of wakefulness, performance is similar to a BAC of 0.08%, and at 24 hours, performance is similar to that seen with a BAC of 0.10%.
- At 22 hours of continuous wakefulness micro-sleeps begin. Micro-sleeps are brief episodes of sleep lasting 3-4 seconds that uncontrollably and spontaneously occur while you are awake.
- According to the SAFTE model and FAST bio-mathematical model, at 17 hours of continuous wakefulness, the operator’s reaction time would have been 122% longer than if he was well rested and not fatigued and many aspects of his performance would have been similar to when he has BAC of 0.05%. See Figure One below.
- According to the SAFTE model and FAST bio-mathematical model, at 22 hours of continuous wakefulness the operator’s reaction time would have been 142% longer than if he was well rested and not fatigued and many aspects of his performance would have been similar to when he has BAC of 0.08%. See Figure Two below.
Interested in learning more about how bio-mathematical modeling can be used as a fatigue risk management strategy? Ask Clinton for a complimentary demo.
 Dawson, D., & Reid, K. (1997). Fatigue, alcohol and performance impairment. Nature, 388, 235.
 Arnedt, T., Wilde, G., Munt, P., & MacLean, A. (2001). How do prolonged wakefulness and alcohol compare in the decrements they produce on a simulated driving task? Accident Analysis & Prevention, 33, 337-344.
 Beaumont, M., Batejat, D., Pierard, C., Coste, O., Doireau, P., Van Beers, P., Chauffard, F., Chassard, D., Enslen, M., Denis, J., & Lagarde, D. (2001). Slow release caffeine and prolonged (64-h) continuous wakefulness: Effects on vigilance and cognitive performance. Journal of Sleep Research. 10(4), 265-276.
 Fatigue Avoidance Scheduling Tool (FAST). Detailed scientific information about FAST and the underlying SAFTE™ model and its validation are available in: Hursh, S., Redmond, D., Johnson, M., Thorne, D., Belenky, G., Balkin, T., Storm, W., Miller, J., & Eddy, D. (2004). Fatigue models for applied research in warfighting. Aviation, Space, and Environmental Medicine, 75(3 Suppl), A44-A53.