When is wearing hearing protection NOT required inside a locomotive cab?

Wearing hearing protection is not required inside a locomotive cab when the cab doors and windows are closed because, in this scenario, the closed environment provides a barrier that helps to significantly reduce the exposure to loud external noises, such as those created by the locomotive's engines and surrounding operations. This isolation can help to keep the noise levels within acceptable limits, allowing the conductor and crew to communicate effectively without having to raise their voices excessively, thus reducing the risk of hearing damage.

In contrast, situations where the doors and windows are open could allow for increased sound levels from the outside environment, which might necessitate the use of hearing protection to safeguard against harmful noise exposure.