______ line leak detectors can detect leaks of 3.0 gph.

• A. External line leak detectors
• B. In-tank line leak detectors
• C. Pressure-based line leak detectors
• D. Interstitial line leak detectors

Answer: (D)

The key idea is that the ability to detect a small line leak depends on where the detector watches for the leak. Interstitial line leak detectors monitor the space between the inner piping and its outer containment. If the inner pipe leaks, fuel enters that interstitial gap, and the detector can sense it and alarm at relatively low leak rates, such as 3.0 gallons per hour. This makes them suited to catching leaks at that rate quickly.

External line leak detectors look for issues around the outside of the piping and aren’t typically tuned to the same interstitial sensitivity, so they aren’t the standard choice for reliably spotting a 3 gph leak. In-tank line leak detectors focus on the tank interior rather than the piping, so they won’t detect line leaks. Pressure-based detectors rely on changes in pressure and may not consistently translate to a 3 gph leak without specific calibration, whereas interstitial monitors are purpose-built for that level of leak detection in double-walled piping.