Final answer:
A qualified person must supervise the installation of a horizontal lifeline, which is an essential component of a personal fall arrest system to ensure workplace safety at heights.
Step-by-step explanation:
A qualified person must supervise the installation of a horizontal lifeline as part of a complete personal fall arrest system (PFAS). In the context of occupational safety and health, particularly with regard to fall protection systems, the expertise and knowledge of a qualified person are critical for ensuring that the system is installed properly and will operate as intended. This involves a wide range of activities such as selecting appropriate anchorage points, determining the system's load capacity, and ensuring that the horizontal lifeline is compatible with other components of the personal fall arrest system. Proper installation of a horizontal lifeline involves careful planning, adherence to specific safety standards and regulations, and often requires engineering knowledge to ensure the system can adequately protect workers who are at risk of falling from heights.