How often should vent pipes be secured horizontally in an ASD system?

In an active soil depressurization (ASD) system, vent pipes should be secured horizontally every 4 feet to ensure stability and prevent sagging or movement that could affect the system's effectiveness. This level of support is crucial for maintaining the integrity of the system, as any displacement of the vent pipes can lead to improper functioning or reduced efficiency in radon mitigation. Adequate securing of the vent pipes also helps to minimize risks associated with environmental factors, such as wind or seismic activity, which might otherwise cause pipes to shift.

The other choices indicate longer distances between securing points. While these distances might seem sufficient in less dynamic applications, they do not provide the same level of stability and reliability necessary for vent pipes in ASD systems, making 4 feet the appropriate choice for this context.