What must always be worn around running aircraft?

Hearing protection must always be worn around running aircraft due to the high noise levels produced by jet engines and other aircraft systems. Prolonged exposure to such noise can lead to hearing loss and other auditory issues. The aviation environment is characterized by intense sound, which can exceed safe decibel levels, making hearing protection essential for safeguarding employees' hearing.

In contrast, while other types of personal protective equipment, such as eye protection, gloves, and hard hats, may also be important in certain situations near aircraft, they are not universally required around running aircraft. Each piece of protective gear serves a specific purpose, but the critical emphasis on hearing protection stems from the constant risk posed by the operational environment surrounding aircraft, where noise is a persistent hazard.