Which of the following is a fall prevention system?

A guardrail serves as an effective fall prevention system by providing a physical barrier that helps to prevent workers from falling off elevated surfaces such as roofs, balconies, or scaffolding. Unlike other options that serve different purposes, a guardrail is specifically designed to prevent falls by creating a protective edge.

Safety nets are also a type of fall protection, but they are classified as a fall arrest system rather than a preventive measure, as they catch a fall rather than prevent one. Hard hats and reflective vests, while essential for worker safety and visibility, do not play a role in preventing falls. Hard hats protect against head injuries from falling objects, and reflective vests enhance visibility, particularly in hazardous work environments, but neither provides a barrier or guard against potential falls from heights.