False alarm probability is defined as the probability of

• A. Correctly identifying a leak
• B. Incorrectly identifying a tight tank as leaking
• C. Failing to identify a leak
• D. Incorrectly identifying a leaking tank as tight

Answer: (B)

False alarm probability is the chance of declaring a leak when there is none. In tank tightness testing, that means a tank that is actually tight being identified as leaking. This is a Type I error: you test positive for a problem you don’t actually have. The other errors are different: correctly identifying a leak is a true positive, missing a real leak is a false negative, and calling a leaking tank tight is also a false negative. So the scenario described—saying there’s a leak when the tank is tight—best fits the idea of a false alarm.