For a 3:1 system to tension highlines, how many persons must be pulling?

In a 3:1 mechanical advantage system, the tension applied through the pulling force is multiplied by a factor of three. This means that for every unit of force applied by the rescuers, three units of tension are created in the system. To achieve the necessary tension to uprate or tension highlines safely and effectively, the number of personnel involved in pulling must match the requirements of the mechanical advantage.

In a 3:1 system, you typically need to have enough capacity in terms of personnel to pull against the load effectively. With this mechanical advantage being factored in, if you have a situation that requires significant tension, the number of people needed to pull will generally be higher.

Given the options listed, the choice that indicates a higher number of personnel (six) reflects a practical approach to ensuring that the force exerted, combined with the mechanical advantage, is sufficient to achieve the desired tension. Moreover, this consideration accounts for the physical effort involved and provides a safety buffer, especially in high tension scenarios.

In summary, the answer reflects a safe and effective number of rescuers needed to apply adequate force in a 3:1 highline tension system.