Why does an entrant wear a full body harness and lifeline?

Wearing a full body harness and lifeline is primarily for ensuring the safety of an entrant in potentially hazardous environments, such as confined spaces. The critical purpose of this safety equipment is to enable quick retrieval in case of an emergency. If an entrant becomes incapacitated or needs urgent assistance, the lifeline allows coworkers to pull them to safety swiftly. This is crucial in situations where visibility may be limited or where conditions quickly change, making immediate rescue necessary.

Other options do not adequately capture the primary function of a harness and lifeline. While it's true that proper safety equipment can help prevent falls, the direct concern during emergencies is the ability to rescue an individual expediently. Additionally, not getting lost and remaining clear of moving machine parts are relevant safety considerations, but they don't specifically pertain to the functionality of a harness and lifeline in emergency scenarios. The lifeline serves as a direct means to ensure the safety of the entrant by allowing for immediate rescue operations.