Which of the following is a release detection method?

• A. Interstitial monitoring
• B. Overfill alarm
• C. Vapor monitoring
• D. Discriminating sensor

Answer: (A)

Release detection means spotting leaks from the storage system into the environment as soon as they happen. Interstitial monitoring fits this because in systems with secondary containment, sensors in the space between the inner tank and outer shell watch for liquid intrusion or pressure changes. If a leak occurs, product collects in that interstitial space, and the alarm is triggered, giving early notice before contamination escapes to soil or groundwater. That direct monitoring of containment integrity is what makes it a release detection method. The other options serve different roles: overfill alarms prevent spills during filling, vapor monitoring checks for hydrocarbon vapors in the surrounding air, and discriminating sensors detect specific vapors but don’t by themselves provide the full release-detection capability.