Laurent Manderson, of Palmerston North Boys' High School, asks :-

Why does a loud noise such as from an explosion cause a ringing sensation in the ears for some time afterwards?

Tim Loads, an audiologist at Wellington Hospital, responded.

Explosive noises can cause damage to cells and structures in our inner ear.

Our eardrums vibrate when a sound reaches them and three small bones transmit the energy of the sound wave to the inner ear which contains thousands of minute 'hair cells'. These move in response to the sound wave and convert the mechanical energy of the sound wave into nerve impulses that are sent to the brain.

When exposed to severe noise exposure, such as an explosion, the damage to the hair cells can range from temporary swelling to complete destruction, depending on the intensity of the noise. As the hair cells are very sensitive to mechanical change, it is thought that the ringing sensation in the ears, known as tinnitus, is caused by the swelling or damage of these cells. Thus the auditory nerve becomes stimulated via the hair cells in the inner ear even though there is no physical sound present. If the damage is restricted to swelling, this will subside after a few days and the tinnitus usually diminishes. A temporary hearing loss can also occur. However if the hair cells are permanently damaged structurally then permanent hearing loss results and the tinnitus may persist.

It is important to protect our delicate hearing mechanism from all loud noises and explosions.