Which safety measure is critical when converting a fixed line to a lowering line?

Tying a Munter mule overhand knot at the anchor point is a critical safety measure when converting a fixed line to a lowering line because it provides a reliable and secure method for managing the transition. This knot allows the rescuer to create a friction hitch that helps control the descent, ensuring that the load can be lowered safely and smoothly. The Munter knot also offers the ability to quickly release the load if needed, while still maintaining security at the anchor point.

Using a different type of rope or a mechanical advantage like a 3:1 system may enhance specific aspects of a rescue operation but does not directly address the immediate needs of safely converting a fixed line to a lowering line. Additionally, ensuring all team members are on the ground is essential for safety, but it pertains to overall operational security rather than the specific process of line conversion. Thus, the Munter mule overhand knot ensures that the system remains robust and reliable during this critical transition phase.