What does a "pretensioned back tie" help achieve?

A pretensioned back tie is primarily used to provide support to a marginal anchor point under load. This arrangement helps to stabilize the anchor by counteracting forces that could potentially destabilize it, especially when the forces acting on the system are significant due to a load being applied. By introducing a pretensioned back tie, the structural integrity of the anchor system is enhanced, allowing it to maintain its position and distribute forces more evenly, thus preventing failure.

This aspect is particularly important in rescue scenarios where the safety of both the rescuer and the victim depends on the reliability of the anchor points. The use of a pretensioned back tie adds a safety margin by reinforcing the anchor without needing to increase the overall tension within the entire rigging setup. It mitigates the risk that could arise from using a single anchor that may not be sufficiently strong on its own.

In contrast, the other options do not accurately represent the primary purpose of a pretensioned back tie. For instance, while it may contribute to tension management in a broader sense, the main focus is on providing the necessary support to the existing anchor points rather than universally reducing tension across all anchors or strengthening the entire setup without the context of load-bearing dynamics.