Under what circumstance may you not use a float line for a single tended diver?

Using a float line for a single tended diver is typically advisable for maintaining visibility and providing safety, allowing for a secured connection between the diver and the surface. However, in situations where there is no access to the surface, utilizing a float line is impractical and unsafe.

If a diver is operating in a location where surface access is restricted, the float line becomes an ineffective means of communication or a safety tether since it cannot reach the surface. In such cases, other methods of ensuring the diver's safety and monitoring their position would need to be employed, as the primary function of the float line—to connect the diver to the surface—cannot be fulfilled.

In contrast, the other scenarios—rough water conditions, strong tidal currents, and night diving—may present challenges for the use of a float line but do not inherently make it impossible to use. Precautions can be taken or alternative methods employed in those conditions to ensure the safety of the diver while still utilizing a float line effectively.