Reaction time for simple tasks:
Reaction time is defined simply as the time between a stimulus and a response. Human reaction time is sometimes quoted as a constant number: 0.2 seconds. While 0.2 seconds may be the average measured for simple tasks, reaction time is actually more complex.
Reaction time for complex tasks:
For more complex tasks such as emergency braking, human reaction time has been studied and measured as three different phases: the time to perceive or sense a danger or hazard (perception phase), the time to make a response decision (decision phase), and the time to respond (response phase). The response phase (i.e. braking) is further complicated by the physical response (i.e. apply the brakes with the foot) and the system response (i.e. the time the vehicle’s braking system requires to actually apply braking force to the wheels). Under ideal driving conditions, the entire human perception reaction time for braking has been measured to be approximately 1.5 seconds (R. Limpert).
Reaction time in work settings:
In the office or manufacturing environments, the human reaction time can be complicated by human factors such as line of sight, sensory overload (i.e. factory noise vs. machine alarms), habituation, sensory deprivation, and environment (i.e. extreme heat or cold).
Additionally human reaction time for a variety of tasks can be greatly impacted by situational awareness and attentiveness. Despite being provided plenty of stimulus for impending danger or hazard, a person who is mentally distracted or unaware of surroundings may never perceive them.
ARCCA has the multi-discipline background to assist incidents where human reaction time and human factors may be an issue.