18.104.22.168 Interstitial Monitoring
Piping systems that use interstitial monitoring are usually constructed of two pipes - a primary pipe inside a secondary pipe. The pipes may or may not be physically bonded together via a series of radial connectors.
The space between the walls of both pipes (commonly referred to as the interstice) is usually very small - typically 1/8 of an inch. This allows for the rapid transport of any leaked product from the primary piping back to the sensor detection point.
Interstitial monitoring relies on the use of a secondary containment space for transporting any liquid that escapes from the primary piping to a sensing point (usually a secondary containment sump). The sensing point contains a sensor that triggers a visual and/or audible alarm or warning message when the liquid touches the sensor.
The advantage of this monitoring method is that it is simple in design and provides a means of secondary containment. This secondary containment prevents any product that may be released from the primary piping from reaching the environment where it can cause damage.
The interstice of double-wall piping systems must be tested for tightness at least once per year to ensure the integrity of both the primary and secondary piping systems.