It is perfectly normal to celebrate New Year’s Eve and Christmas with fireworks. Here in the Comunidad Valenciana are still numerous local celebrations like Fallas, Moros y Cristianos, weddings, parties, and more that usually are celebrated with blasts and fireworks. But do you know why many attend this spectacle open-mouthed?
With heavy noise the eardrum absorbs a lot of energy, which also flows to the Eustachian tube. This has the function to compensate for the different pressure of middle ear and eardrum compared to the external pressure. But if this pressure difference is very large, it is better to help somehow.
When the mouth is open, the energy that comes through the eardrum is compensated and neutralized by the energy through the Eustachian tube. Thus, the inner ear is less affected.
Incidentally, this is not only true for fireworks but also for very loud music.