Which of the following can be considered a collective fall-arrest measure?

The choice of safety nets as a collective fall-arrest measure is appropriate because they are designed to catch a person who falls from a height, thereby preventing injury. Safety nets are installed below areas where work at height is taking place, and they provide a collective means of protection for multiple workers in a given area. They are effective because they do not rely on individual behavior: as long as the nets are properly installed and maintained, they offer a safeguard to all personnel who may be at risk of falling.

In contrast, personal fall harnesses are considered an individual fall-arrest measure, as they rely on the user's correct usage and attachment to a secure point. Hard hats, while necessary for head protection, do not address the issue of falls from height. Warning signs serve to alert workers about hazards but do not provide physical protection against falls. Hence, safety nets effectively represent a collective preventive approach, protecting groups rather than relying solely on individual precautions.