Final answer:
According to OHS Code Part 9, a worker must wear a full body harness when using a personal fall arrest system.
Step-by-step explanation:
According to the OHS Code Part 9, when using a personal fall arrest system, a worker must wear a full body harness. This type of harness distributes the forces of a fall over the body's strongest parts, including the shoulders, chest, and legs, reducing the risk of injury. In contrast, a chest harness, waist harness, and shoulder harness are not recommended for use as the primary harness in a personal fall arrest system since they do not provide adequate support and may lead to serious injuries.