Our hearing mechanism is one of the five senses and we only have two ears to last our entire lifetime. Once they are damaged they can never be repaired. We spend more time exposed to harmful levels of sound than ever before, at work and also in our free time.

If you are affected by Noise Induced Hearing Loss (NIHL) you can never get your hearing back. Rehabilitation or hearing aids can soften or improve the effect slightly, though will never bring back your hearing to what it was prior to the NIHL. Hearing loss can significantly affect your ability to work as well as having a detrimental effect to your social life as it can leave an individual feeling isolated and anxious due to not being able to engage in conversation. Therefore, prevention is the best cure.

How does sound occur?

These waves are transmitted through the air and received in the eardrum. They then move through into the middle ear into the cochlea that is situated within the inner ear. The cochlea contains thousands of tiny hair cells with nerve endings 30,000 (stereocilia).

The cells move when sound waves reach them which are transferred into impulses that are transported to the brain via the auditory nerve. These waves become sound. When the nerve endings (stereocilia) are constantly exposed to harmful, excessive levels of sound they will break off, eventually disintegrate and never regrow. The surviving stereocilia can only handle a fraction of the information being transferred to them as permanent damage has now been caused.

Tinnitus

One of the most common effects of NIHL, often referred to as a ringing, buzzing or whistling sound in the ears, is tinnitus. This can be caused by temporary exposure and may pass after a time. However, after continual exposure it is common for tinnitus to become permanent. This form of tinnitus is not medically treatable and can cause great despair and pain to a person’s life, activities, work and most particularly sleep patterns or quiet time as it can become incredibly debilitating.

When does noise become harmful?

We are aware of various hazards in industry, however unlike damage to the eye, head and respiratory system, hearing loss is not necessarily painful at the time nor is it visible either.

We should view noise as a physical hazard and prolonged exposure can result in a physical cumulative type of injury. The chance of injury from noise is a combination of two factors:

1. Weighted sound level – dB(A)
2. Length of time exposure to these elements As an example: fifteen minutes exposure to 100dB(A) contains the same level of energy as eight hours exposure at 85dB(A). If the sound level increases by 3dB(A) the power and energy are doubled.

Decibels and Hertz

Sound is measured not only in its intensity (Decibels - dB) but also its frequency/ pitch (Hertz - Hz). The range of frequencies that the human ear can perceive is quite wide, typically 20-20,000 Hz. However, the most sensitive range that we can hear is generally 500-4,000 Hz. Unfortunately, these can be very easily damaged if exposed to high decibels levels within that frequency range.

What is the difference between dB(A) and dB(C)? An (A) weighted sound correlates to the way the human ear hears sounds and a somewhat low level.

Whereas a (C) weighted sound correlates to how the ear hears louder sound levels and is measured without the suppressing of lower frequencies. Often impulse sounds (that last one second or less) can be measured as (C) weighted.

What is SNR?

SNR refers to Single Number Rating. This can be used to ascertain the average level of noise reduction achieved from a hearing protection device as well as to compare the level of noise attenuation offered by different hearing protection equipment.

Regulations

The Control of Noise Regulations 2005 came into force on 6th April 2006 for all industry sectors (other than music and entertainment for which this came into force from April 6th 2008) (http://www.hse.gov.uk/noise/my...) http://www.hse.gov.uk/pubns/in...

The document ‘Control of Noise Regulations 2005’ replaces the Noise at Work regulations from 1989. It suggests the level for which employers should provide hearing protection is 85dB(A) or the second action limit (previously 90dB(A)). For daily or weekly average exposure, the level at which employees must assess the risk to workers is now 80dB(A) or first action limit (previously 85dB(A)). There is also an exposure limit to consider when an individual is wearing hearing protectors to the value 87dB(A). This should take into consideration the reduction of exposure by providing hearing protection equipment above which workers must not be exposed.

Risk assessment procedure

1. Has this been carried out, if so what are the typical noise level hazards?
2. Has a noise survey been carried out to establish the levels of sound? If so what are the next steps?
3. Could the steps be taken to reduce the noise?
4. Has consideration been given to the time exposure?
5. Provide appropriate hearing protection.
6. As PPE is considered the last defence, what hearing protection is being considered and on what basis (performance, appearance, comfort, financial)?
7. Provide training on the use of hearing protection equipment as well as information relevant to the risk and control measures.
8. Provide audiometry testing for those whom the risk assessment has determined are working with in the upper (second) action limit.

Action limit and values

An action limit is a noise exposure level at which employers are required to take certain steps to reduce the harmful effects of noise on hearing. There are two main action levels for continuous noise:

Lower action values: 80dB(A) 112pa (135dB(C)) impact Hearing protection should be made available and optional. Training should be given. Upper action value: 85dB(A) 140pa (137dB(C)) impact Hearing protection is mandatory. Audiometry testing is required. Training should be provided.

Exposure limit value:

87dB(A) 200pa (140dB(C)) impact

This exposure limit must not be exceeded when wearing hearing protection.

List of hearing protection standards

Selecting the right type of hearing protection

Types of ear protectors

Ear plugs

Ear plugs can be worn easily and for extended periods of time in many varied climates and industries. They also can be worn along with other PPE such as safety spectacles and dust masks. However, as they are less visible than ear defenders the supervising of correct fitting can be a challenge. Whilst ear plugs now come in wide variety of sizes, shapes, colours and materials, care must still be applied when preparing them for insertion. They do require an element of skill and attention to achieve a successful fit.

Roll down ear plugs

Most often roll down plugs are made from polyurethane (PU) or polyvinyl chloride (PVC) and tend to be for single use. The greatest benefit of these is comfort as well as being a ‘one size fits all’ product (though not in every case!). They are also easy to distribute via wall mounted dispensers.

How to fit:

With clean hands, roll and compress the plug into a crease-free cylinder.

With the other, reach behind the head to grasp the pinna (outer fleshy part of the ear) pulling gently up and outwards.

Take the rolled down ear plug (still compressed) up to the ear and insert into the ear canal.

The ear plug will then start to slowly expand to its maximum capacity whilst taking up shape of the ear canal It is advised to hold your finger gently against the ear plug while it is expanding to help maintain its position. When fully expanded the plug will significantly reduce the noise level reaching the ear. This will be noticed by the wearer and can be used as a simple check for fitting correctly.

Whereas pre-moulded ear plugs can be adjusted slightly whilst in the ear it is recommended that roll down ear plugs are not. Instead the wearer should remove them if the fitting seems poor. In such circumstances, they should be re-rolled and inserted again.

Roll down plugs offer protection levels from 21 to 39 SNR.

Pre-moulded ear plugs

These are made from pliable materials such as thermoplastic rubber (TPR), cured silicons and other elastomeric elements. Nearly all are available with cords attached to help prevent loss. This type of earplug also lends itself to being re-used, normally for several weeks or possibly months, depending on the style, working environment, hygiene and body chemistry. They should be replaced if they become damaged in any way and should be cleaned carefully in warm soapy water daily drying thoroughly and storing in the supplied case where applicable.

How to fit:

Insertion of these is by the same method as detailed above – by pulling the pinna gently up and outwards whilst applying the pre-moulded plug into the ear canal with a twisting motion. This method (twisting) should also be applied when removing the ear plug.

If the pre-moulded ear plug is situated correctly in the ear canal it will generally give the impression of a blocked feeling in the ears to the wearer due to achieving an airtight seal. Users could also experience a resonance, ‘bassy’ or muffled tone to their voice (occlusion effect). If this does not occur then a re-fitting of the ear plug should be actioned. When both plugs are correctly seated the individual should notice his or her voice appearing to originate from the centre of their head. There are a wide variety of pre-moulded earplugs with varying levels of protection from very low 14 to 35 SNR.

Semi-aural hearing protectors

These types of hearing protection tend to have pods/buds or flexible pre-moulded tips (which should be replaced over time for good hygiene) attached to a headband that will sit around the back of the neck or underneath the wearer’s chin.

They are very easy to fit allowing the pod to sit over the opening/entrance to the ear canal creating the occlusion effect as described earlier.

How to fit:

Hold the ends of the pods and direct them into the opening to the ear canal

Firmly push and wiggle the pods into place until a snug fit is reached

Pulling on the outer ear while pushing the pods will afford the wearer a good fit

These are ideal for workers required to wear hearing protection sporadically whilst also being mindful of possible contamination on their hands – should they be inserting a roll down type of ear plug. In such instances, the semi-aural banded hearing protectors can hang around the neck until required.

Protection levels can range from 21 to 28 SNR.

Custom-moulded ear plugs

Custom made ear plugs are usually manufactured using two–part curable silicone or a membrane that is injected with medical grade silicone from a moulding of the individual’s ear canal and a portion of the concha, taken by a technician.

There is a high level of skill required to achieve a good fit when taking the moulds. By the fact that such ear plugs are custom made does not mean they will provide better protection than other types of well fitted ear plugs. It is also worth considering that climate, temperature (the ear canal expands and contracts with seasonal changes) and poorly taken mouldings can lead to a wearer not achieving an acoustic seal. This can allow harmful noise to leak around the sides of the ear plug whilst in situ unbeknown to the wearer. Many of these devices are not tested when manufactured for their acoustic seal qualities. However, there are some companies, particularly those that supply into the entertainment sector, that are quite diligent in their process of facilitating custom–moulded hearing protection.

Low attenuating hearing protectors

These are protectors that offer a small amount of protection (typically 20 -25 SNR) whilst allowing a wearer the ability to hear warning alarms, communication and machine sounds without them feeling isolated.

Typically, these are ideal in areas where the maximum noise level is 98dB(A) where they will reduce the level down to 70-80dB(A) (see EN458) at the wearer’s ear.

These products generally tend to be semi-aural banded and pre-moulded reusable earplugs. Typical industries requiring low attenuation earplugs include: food (production / packaging) printing, recycling, aerospace and electrical engineering.

Ear defenders

These consist of rigid moulded plastic ear cups that cover the ear by means of foam or fluid filled cushions.

They are held in place by a metal or plastic band or clips attached to a safety helmet.

The cups are usually lined with an acoustic foam. This is intended to absorb the higher frequency energy present within the cup. Ear defenders are very easy to allocate to staff, as generally one size will fit all however staff should be evaluated and trained in the correct use and fitting when the product is first issued – as head and ear sizes may not fit the headband or the ear cups.

It is necessary the ear defender cup covers the wearer’s ear at all times whilst exposed to noise levels at and above the second action limit.

Instruction for the correct wearing and usage must be given when ear defenders are issued.

The performance of this type of hearing protection can be ultimately compromised by anything that comes between the cups and the wearer’s skin such as eyewear, hair, masks, face shields and safety helmets.

Typical levels of protection with ear defenders range from 19 to 37 SNR.

How to fit:

The ear defender cup should fully cover the ear with the cushions resting on the side of the head.

Care should be taken not to place the cushions over the sides of the ears (on an ear defender with an ‘A’ band, the headband should go over the top of the head as per manufacturer’s instructions) ensuring the ears do not protrude from under the ear defender as this will result in harmful levels of sound (dependent on time exposure) causing possible long-term damage.

It is critical the ear defender is worn 100% as intended, thus offering the ideal protection. Staff need to be made aware of the seriousness of inadequate protection and the implications.

Other types of hearing protection

• Level dependent ear defenders: These protect from harmful levels of noise but allow an increase in sensitivity to certain frequencies without allowing damage to the hearing mechanism

• Communication devices: Usually ear defenders with radio built in, either open mic (dect comm) or two-way communication using free wav bands

• AM/FM/MP3 /iPod/phone radio’s: These allow the wearer to enjoy music whilst still being protected from the harmful levels of sound around them. The digital device would be connected via a 3.5mm jack. As they listen to the content, the ear defender has a built-in level attenuator that doesn’t allow the level to go above 80-82dB(A).

Training

Staff need to be aware of the delay (typically 5-7 (what?)) before the advent of NIHL takes effect. Ordinarily the loss of recognition of consonants is the first indication (s’s and t’s from human speech). This is the challenge, particularly when we surround ourselves with noise every day.

• Offer usable solutions by considering the noise in the work environment of an individual

• Demonstrate how to fit, maintain and store hearing protection

• Consider compatibility with other PPE

• Use a positive approach to hearing conservation via testimonials as well as utilising our solutions-based approach.

And finally

Consider this;

“Blindness cuts us off from things, but deafness cuts us off from people”

Helen Keller

(American deaf-blind author, activist and lecturer, 1880-1968)