What is the minimum distance required for an air gap in a drainage system?

The minimum distance required for an air gap in a drainage system is twice the diameter of the indirect waste pipe. An air gap is a physical separation between the end of a waste pipe and the fluid level in a receptor, such as a sink or drainage basin, designed to prevent backflow and potential contamination of potable water systems.

This specification helps ensure that there is sufficient vertical distance to prevent siphoning and to create an effective barrier against the possibility of backwater entering the potable water supply. The requirement for twice the diameter of the indirect waste pipe allows for variations in flow and accounts for the potential turbulence and movement of fluids during drainage events.

In contrast, other options do not provide the necessary assurance of a safe air gap. The diameter of the waste pipe on its own may not guarantee sufficient protection, while specifying five feet from the flood level rim lacks the necessary specificity regarding the pipe diameter and flow dynamics. The equal height of the drainage pipe does not address the need for separation adequately in terms of ensuring safety against backflow risks.