A loss of any form of sensory input is a life changing event. Consider our ability to perceive sound; the accumulative destruction of hearing over time can and will be devastating to the individual concerned.
Whilst hearing sensitivity does decrease with age, the risk of accelerated loss can be worsened by exposure to excessive noise sources; explosions, plant equipment, loud music and other occupational noises.
This risk can be managed and avoided to prevent such a terminal consequence.
Noise Induced Hearing Loss (NIHL)
The human ear perceives noise by mechanical transmission; put simply, this is caused by sound pressure waves being broadcast through the outer ear to the inner ear. Visualise a still lake and imagine standing on the shore; throw a massive rock into the centre of the lake – the ripples spreading out to the shore are how sound transmits in the air as a medium.
These waves are directed via the outer ear to the next stage, which is the middle ear; this consists of three small bones called the ossicles – also known as the hammer, anvil and stirrup. The hammer is attached to the eardrum; together with the anvil it forms a lever that controls the stirrup. As the sound energy waves hit the middle ear transmits the resultant force into the fluid of the inner ear. Visualise a tiny drumstick beating a drum in one room, yet making a massive boom, boom, boom in the aquarium next-door.
The final part of the ear, is the complex inner ear, this is a complex array of tubes and chambers embedded in solid bone. The part concerning hearing is the cochlea, a spiral hollow that resembles a snail shell!
This has some 30,000 highly receptively sensitive hair cells. The pressure waves transmitted into the cochlea fluid ‘warp’ the hair cells; this in turn stimulates the nerve endings at their base, firing off a nerve impulse into the auditory centres of the brain. This is then encoded by the brain into its interpretation of ‘sound’.
However be aware that these hairs are not indestructible …
Visualise a peaceful forest, rich with tall majestic trees. The trees sway gently in the breeze. In high winds they may bend, but eventually return to their original positions, undamaged. Detonate a thermonuclear device and these trees will be completely decimated; there is nothing to spring back. This is what happens to the cochlea during an event that leads to a permanent threshold shift (PTS).
The human hearing range is quite limited in the spectrum of sound; 20 Hertz to 20 kilo Hertz is the functional factory delivery pre-set. As a comparison:
- dolphins and bats can hear up to 100 kilo Hertz, which is ultrasonic
- elephants can perceive sounds at 14-16 Hertz, they perceive infrasonic trunk calls
- whales are amazingly subsonic, clocking in at a plankton guzzling 7 Hertz
Exposure to excessively loud sound sources, or ‘noise’ can result in transitory sensory deprivation, usually through a temporary threshold shift (TTS).
However, this hearing condition will reset, depending on the dose of noise received. The dose is determined by two factors; the noise intensity (dB) and the duration of the exposure.
This is how loud the noise is and how long your ears are being blasted by it. Always be aware that extremely loud noise causes some form of damage every time! Yes, you heard correctly…every time.
Should you continue to be exposed to the noise source, over time, a permanent threshold shift (PTS) will occur leaving hearing perception irreversibly damaged. There is, at this time, no medical treatment or corrective surgery available for this event; there is no going back and no reset the following day.
This is the first tentative step on the ever frustrating one-way street of impaired hearing. In some cases, this can give rise to another related hearing issue; tinnitus.
Tinnitus can literally drive a person to the edge of madness. Globally, millions of sufferers become so affected by the incessant ringing, hissing, chirping, clicking, whooshing and screeching, that they can struggle to engage in the simplest of daily activities.
Tinnitus can occur after exposure to extreme noise as an acute condition, which ‘resets’ after time. This can be after a night of clubbing with extremely loud music for example; it can often take 12 hours or more for this to happen. If this damage is repeated over time, the reset takes longer until there is nothing left to reset.
The incremental damage that leads to tinnitus wreaks just as much havoc on our cochlea ‘trees’ as a single PTS event.
This should and CAN be avoided at all costs with the use of hearing protection in the form of ear defenders, ear plugs or muff type protectors.
Always remember to:
- be aware of what generates noise hazards
- control the noise hazard at source if possible
- use ear protection
THSP Risk Management have Institute of Acoustics qualified and experienced consultants who, using the most up to date equipment, can carry out an assessment of exposure to noise in your workplace. We will then recommend appropriate control measures and identify where improvements can be made to fulfil legal obligations. For more information click here or call us 03456 122144.
Written by Lucian D’Arco.