Why do artillery soldiers open their mouths when firing a gun?

At the moment the cannon is activated, the gunpowder in the projectile is triggered by the primer, causing a deflagration. In addition to pushing the warhead out of the barrel, the gunpowder gas will also produce huge noises. Under the impact of a large amount of instantaneous noise, it is very possible for artillery at close range. Due to the huge noise of the shells, a large amount of air pressure is generated.

After the strong vortex enters the ear canal, the huge air pressure difference between the inner and outer ear canals will cause the tympanic membrane to be torn, and the surrounding capillaries may also be shattered by the huge noise. It even causes internal organ damage, so the artillery at close range must protect their important hearing organs and ears.