What is the appropriate height for an air gap in relation to the diametric size of the pipe above the flood rim of a vessel?

The appropriate height for an air gap is twice the diameter of the pipe. This standard ensures that there is adequate separation between the supply water and any potential contaminants. By having an air gap that is twice the pipe diameter, it provides an additional safety margin to account for fluctuations in pressure and water flow, which could otherwise allow backflow under certain conditions.

In various plumbing codes and standards, the air gap is crucial in preventing cross-contamination between potable and non-potable water systems. The importance of the air gap cannot be overstated, as it acts as the first line of defense against back siphonage and other forms of reverse flow that might introduce harmful substances into the drinking water supply.

This requirement strengthens the integrity of the plumbing system and promotes public health by ensuring a reliable safeguard against potential hazards. Other options do not provide the same level of protection or fail to meet commonly accepted plumbing standards.