Health

H

Dr Rod Pearce

HEALTH

Noisy environments a danger to hearing

Hearing loss can be an occupational hazard which usually results from noise (noise-induced hearing loss, NIHL).

Noise damage to the ear itself occurs because of exposure to intense impulse or continuous sound.

When we talk about sound, we talk in terms of high- and low-frequency waves. Sound waves are movements of air molecules that our ears translate into sound, and frequency refers to the number of cycles these waves complete in a second.

Low-frequency sounds are 500 Hz or lower while high-frequency waves are above 2,000 Hz. Human ears can register sounds from about 20 Hz up to 20,000 Hz, depending upon the hearer.

People with hearing loss usually have trouble hearing sounds in the higher frequency range. Speech usually falls within the 100 to 8,000 Hz range. People might start to find difficulty in discerning speech once it exceeds about 3,000-4,000 Hz.

Five-hundred Hz will create a rumbling sound in the lower frequency and you might feel the sound as much as hear it.

A sound in the 500-2,000 Hz range will have a tinny or horn-like quality (medium-frequency sounds). Higher frequency sounds (usually above 2,000 Hz) are mostly within our hearing. When it gets up to the 10,000 Hz, it is the crashing cymbals or chirping birds. Ultrasound is a frequency (above 20,000 Hz) and too high for us to hear.

In general, the tone at which we speak lies in the range of 100-120 Hz for men, but variations outside this range can occur. The pitch for women is around one octave higher. A child’s speaking voice is around 300 Hz. Many have thought shooting only once or twice a year was unlikely to cause hearing loss. But in reviewing cases of acute acoustical trauma from gunfire, over 40 per cent had noticeable acoustical trauma caused by a single shot.

The greatest amount of hearing loss is typically around the 4,000 Hz region, known as the “4,000 Hz dip”.

Problems with your hearing might present in different ways. It is important to get checked out if you have any concerns.

Symptoms include: • Tinnitus (ringing in the ear). • Fullness or pressure in the ear. • Hearing loss. • An occasional feeling of dizziness. • Difficulty hearing high-pitch sounds (birds, women’s and children’s voices). • Difficulty understanding speech in background noise. • A decrease in hearing very soft or very loud sounds.

The reason police work causes hearing loss probably has as much to do with working in noisy environments as it has from using firearms. But any use of guns is associated with NIHL.

Many have thought shooting only once or twice a year was unlikely to cause hearing loss. But in reviewing cases of acute acoustical trauma from gunfire, over 40 per cent had noticeable acoustical trauma caused by a single shot.

Ninety-two per cent of all these traumatic incidents occurred within two metres of the firearm. Most (83 per cent) wore no ear protection when the traumatic episode occurred. The more you shoot, the more chances of having a gun go off near your ear.

Occupational hearing loss is a well-recognized condition which arises from industries or occupations (such as airline crews) with exposure to high noise levels.

Many studies have been undertaken to assess the link between hearing loss and gunfire by military personnel. Only a few similar studies have been conducted in respect of police officers.

Police officers are potentially exposed to multiple sources of noise, including vehicle horns, barking police dogs, and traffic noise. For police motorcycle officers, the noise exposure can range from 63 decibels to 90 decibels, and up to 105 decibels on open roads.

In a normal ear, the auricle (pinna) is the visible portion of the outer ear. It collects sound waves and channels them into the ear canal, where the sound is amplified.

The middle ear functions to connect the sound waves from the external environment and transfer them to the inner ear. Middle ear anatomy consists of intricate relationships between nerves, blood supply, and muscles.