The muzzle blast from a powerful muzzle brake equipped rifle is so loud that even with hearing protection the shooter risks suffering some permanent hearing damage after a few shots. Earmuff type hearing protectors typically reduce noise by about 25 dB. A muzzle brake equipped magnum rifle (like a .300 or .338 Magnum) produces a sound pressure level (spl) in the 130-dB range, according to reports I have read. Thus the spl inside the hearing protector is in excess of 100 dB, a potentially damaging level.
For a hunter in the field, shooting without ear protection, the muzzle blast from a muzzle brake is immediately deafening. Nearly complete temporary deafness usually lasts from about a minute to several minutes after firing a powerful magnum rifle equipped with a muzzle brake. Later almost all of the shooter's hearing returns, but a certain amount is permanently lost, and the losses are cumulative.
This is why hunting rifles equipped with muzzle brakes are illegal in some African jurisdictions. They have proven damaging to the unprotected hearing of the scouts and guides accompanying the hunter. In North America an increasing number of big game guides now refuse to let a sport use a rifle equipped with a muzzle brake for the same reason.