According to DoD standards, when should an audiometry baseline be established?

Establishing an audiometry baseline after entering active duty and prior to noise exposure is critical for monitoring hearing health in military personnel. This baseline serves as a reference point to detect any changes in hearing that may occur due to occupational noise exposure. By conducting the initial assessment before any exposure begins, it enables the detection of hearing degradation related specifically to military duties, as opposed to pre-existing conditions.

Waiting until noise exposure has begun, as suggested in the other options, does not allow for a clear comparison of hearing changes attributable specifically to the military's noise environment. Regular annual assessments or doing so after a certain period of exposure will not provide the necessary baseline data that is vital for identifying potential hearing loss caused by work-related factors. Therefore, establishing the baseline prior to any noise exposure is essential for ensuring adequate hearing conservation measures and protecting military personnel from permanent hearing loss.