What is the Pi value (Probability of incapacitation) used for risk-estimate distances?

• A. 0.01%
• B. 0.1%
• C. 1%
• D. 0.001%

Answer: (A)

Pi is the probability of incapacitation from a hazard at a given distance. When you determine a risk-estimate distance, you set a very small, fixed Pi as a safety threshold and find the distance at which the chance of incapacitation equals that threshold. That boundary defines the RED.

Choosing 0.01% (one in ten thousand) as the threshold provides a conservative but practical boundary: it keeps the probability of incapacitation at or below a very small level while not requiring unrealistically large distances. Higher thresholds would allow closer distances with greater risk, while even smaller thresholds would be excessively conservative and widen the RED further. Therefore, 0.01% is the standard Pi value used for risk-estimate distances.