What device must be provided unless a self-closing nozzle is used?

The requirement for an anti-siphoning device arises from the need to prevent the backflow of fluids in systems that could result in contamination or failure of safety measures. In the context of fire protection systems, when a self-closing nozzle is not used, an anti-siphoning device is essential to ensure that water or fire suppressant does not siphon back into the supply lines, which could lead to hazardous situations, especially in scenarios where non-potable water may be present.

This device acts as a safeguard by ensuring that the flow of the liquid only goes in one direction—toward the fire suppression area and not back into the supply source. Implementing this measure protects both the system's integrity and public safety.

Other devices mentioned, such as fire suppression systems, pressure monitoring gauges, or filtering systems, serve different functions and do not directly address the issue of fluid backflow in the same way that an anti-siphoning device does.