Which of the following is NOT a type of hearing protection device?

In the context of hearing protection devices, earplugs, earmuffs, and noise-cancelling headphones are all specifically designed to reduce the impact of loud noises and protect hearing. Earplugs fit directly in the ear canal, while earmuffs cover the entire ear. Noise-cancelling headphones can electronically reduce background noise in addition to functioning as sound-isolating devices.

Dust masks, on the other hand, are designed to protect the wearer from inhaling harmful dust, particles, and allergens, rather than to safeguard hearing. They do not address noise exposure and thus do not serve the purpose of a hearing protection device. Therefore, this makes dust masks the choice that does not belong in the category of hearing protection devices.