Which of the following is a necessary component of a full body harness system?

A full body harness system is designed to protect workers from falls while ensuring they are secured and stable at height. The key component of this system is a deceleration lanyard, which connects the harness to an anchor point. In the event of a fall, the deceleration lanyard absorbs the energy generated by the fall, reducing the impact on the body. This feature is vital as it helps prevent injury by slowing down the fall before the person reaches the ground.

In contrast, while the other options may enhance comfort or provide additional support, they do not constitute essential components of a full body harness system. For instance, a chest strap by itself does not provide the full body support necessary to ensure safety, as it may not adequately distribute the forces experienced during a fall. Arm straps and ankle supports may offer some security, but they do not fulfill the critical role of fall arrest that the deceleration lanyard serves. Hence, the inclusion of a deceleration lanyard is fundamental to the effectiveness and safety of a full body harness system.