Hearing loss is far more common than one may expect. In 2005 the RNID, now Action On Hearing Loss, conducted a study amongst a group of 20,000 respondents. The results suggested that over 10 million people in the UK alone are thought to have some level of hearing impairment; with the most common reasons for the loss linked to age-related and noise-induced causes. The two causes could not be more different. Whilst age related hearing loss is a natural process that people can do little about, the same cannot be said for noise induced hearing loss.
So, how do we hear and what can go wrong?
The process of hearing, like many other functions in our sophisticated bodies, is a complex process. For the purpose of this article, we will simplify how our sense of hearing works. Hearing is the ability to capture waves of sound and to translate the sound into signals for the brain to interpret. The ear has three parts, which are all required for the normal hearing process: the outer, middle and inner ears.
Sound waves enter the ear canal, the visible outer ear portion helping to direct them there, and make their way to the eardrum. The changes in pressure causes the eardrum to vibrate. These vibrations reach three tiny bones in the middle ear (the ossicles). The ossicles are responsible for transmitting the sound through to the fluid-filled inner ear. Within the inner ear, specifically the cochlea, specialised sensory cells known as hair cells send electrical signals through the hearing nerve to the brain to make sense of the sound. There are many things that can go wrong and affect our ability to hear.
When these special sensory cells deteriorate or are damaged due to the natural ageing process or due to prolonged exposure to excessive noise, hearing loss may occur. The level of hearing loss present (measured in dB against normal hearing) will vary from one person to the next depending on the severity of the damage and other conditions that may also be present within the ear. The two most important factors contributing to noise induced hearing loss are:
- The level of noise the person was exposed to
- The duration of the exposure
The tiny sensory hair cells that are crucial to our ability to hear cannot regrow or regenerate and any level of hearing loss that is caused due to hair cell damage is likely to be permanent.
Preventing noise induced hearing loss:
Noise induced hearing loss can be broken down further into two types, acoustic trauma and loss caused by repeated, prolonged noise exposure. Increasing loss is caused by repeat exposure to harmful levels of sound, typically over 85dB, while extreme acoustic trauma is caused by a sudden unexpected loud noise source, for example an explosion.
By law, UK businesses are obligated to do as much as possible to prevent noise induced hearing loss from occurring at work. Under the 2005 government noise regulations, businesses are required to target areas with noise levels of 80dB and 85dB and provide ways to minimize risks to employee’s hearing health. Typically the efforts will be led by a health and safety consultant to ensure that accurate reading of noise is carried out.
When daily noise levels reach 80dB businesses must:
- Explain the risks of hearing loss to their employees
- Provide hearing protection such as earplugs and earmuffs and training
- Move to quieter processes and quieter machinery where possible
- Continue to monitor noise levels on a regular basis
When daily noise levels reach 85dB businesses must:
- Follow the guidelines above
- Make wearing hearing protection mandatory (by law not subject to one’s discretion)
- Mark the noisy areas clearly using visible signs
- Install sound reduction equipment together with removing noisy equipment
- Note that after taking into the reduction in dB due to using hearing protection (typically 20dB reduction for earplugs and slightly more for earmuffs depending on their standard) noise should not exceed 87dB on average and 140dB in peak
When noise is suspected of exceeding permitted levels, a risk assessment needs to be taken. The assessment should be conducted by a health and safety professional to ensure that the advise, information and solution offered complies with UK laws.
Joan McKechnie BSc Hons Audiology & Speech Pathology at hearing aids company Hearing Direct. You can read her blog for more information on hearing loss.