Hearing Protection

Controlling noise exposure at work is mandatory in many countries and industries, and is recommended by international standards.

Very high noise levels, for example from blasting, shooting and close proximity to jet engines can cause instantaneous hearing damage, but lower levels of noise can cause damage over a period of time that may only become apparent years later.

Where the noise cannot be controlled at source or by reducing the transmission path, hearing protection will usually be required. There is a variety of hearing protection available, and this should allow protection to be selected that does not conflict with other above the neck protection, such as hard hats, visors or eye protection.

Background

Hearing is a complex mechanism whereby vibrations in the air are converted by the thousands of tiny hairs within the inner ear into electrical signals, which are received by the brain. Individual hairs can be damaged by high sound levels but the remaining hairs still allow reasonable hearing. Unfortunately, hairs become damaged or weakened with age, and if some of the hairs have been previously damaged, hearing may be lost in middle or late age, due to damage sustained years ago. It is therefore important to protect the hearing of workers, even if there are no apparent signs of hearing loss.

Most countries set noise action levels to limit noise exposure; typically first, second and peak action levels. Above the first action level the employer has a responsibility to take some measures to monitor and control noise, and hearing protection is encouraged but may be optional. If noise exposure exceeds the second action level, hearing protection becomes mandatory and the employer may be required to mark out a noise protection zone.

Risk assessment

Most regulations and guidance require a workplace noise risk assessment to be undertaken. The assessment should be undertaken by a competent person, and needs to assess the noise generating plant or machinery, the transmission path between the source(s) and any exposed persons – which may be employees or members of the public. The assessment should also consider the work practises of exposed persons. For example, do they do the same job all day, or are the tasks varied with some noisy and some quiet activities?

Depending on the nature of the work and the available data the assessor may be someone familiar with workplace risk assessments but limited specialist knowledge of noise. For example, if the manufacturer has measured the sound power level and marks this on the machine, or states it in the handbook or datasheet, a desktop assessment can calculate the operator’s exposure if the operating position and hours of exposure are known. For complex workplace environments, however, a specialist acoustic consultant may be required; for example, if the equipment noise depends on the material or task being worked, or the position of the operator in relation to the noise varies.

Some countries require manufacturers to provide noise data for equipment producing noise levels likely to exceed action levels, but such data does not usually allow for the acoustic of the operating environment, or the material being worked. A power saw used on a building site on a small plank may produce a very different noise level inside a building cutting a large sheet.

Where measurement is necessary it should take place at the workstation without the worker present using a sound level meter. Where the operator moves about, a small meter with a built in or clip on remote microphone, called a ‘dosimeter’ may be used. Often a mixture of sound level meter ‘spot measurements’ and dosimetry is required.

Each employee’s daily noise dose will depend on:

• The different tasks that are performed

• The duration of each task

• The environment the tasks are performed in

The noise risk assessment should identify persons exposed above the action levels. This may be a class of employees; for example, workers who operate a particular machine, or particular individuals such as a maintenance engineer who needs to remove guards or control measures to check equipment.

Exposure levels

In some cases it may be possible to present a map with contours indicating noise levels across a range of areas. It is, however, normally more appropriate to identify the persons or workstations exposed above the action levels. Charts can also be prepared showing proposed noise action zones where the first, second and peak action levels may be exceeded. The daily exposure levels assume that a person is exposed to the same noise exposure level each day. Where the worker performs different tasks on different days it may be possible to calculate a weekly noise exposure.

Where possible, noise should be mitigated by using quieter equipment or processes. Often this approach has added benefits including improved energy efficiency – noise is energy being lost to the atmosphere, after all.

Where it is not practical to reduce the noise at source, barriers or enclosures can be used to reduce the transmission path. If this is not possible, personal hearing protection may be the most practical solution.

Guarding against noise

Relying on personal protection is identified in UK guidance as a last resort. In some cases a task or equipment may exceed the action levels only if used for extended periods. In this case a control measure may be to specify that hearing protection should be used if the machine is operated more than a certain period of hours in any one day.

There is a wide range of personal hearing protection available and it may be confusing for both employers and employees to select the correct solution.

The first point to realise is that there may be more than one correct solution.

There may also be different solutions for different individuals.

There are two main types of protection: in-ear protection, or earplugs, and over-ear protection, or earmuffs.

In-ear protection varies from simple disposable foam plugs to individually custom moulded plugs with inserts. Foam plugs can provide a good level of protection, and may be suitable when different staff need to spend short periods in a noisy area such as a building site. The simplest foam plugs need to be rolled and compressed before fitting in the ear.

Everybody’s ear is slightly different and in the Nineteenth Century scientists considered using ear prints in place of fingerprints for identification.

Moulded earplugs avoid the need to compress before fitting, so are easier to fit for many people and can be reused.

Custom mouldings can be fitted with an attenuator or, for people who need to communicate in noisy environments, an earpiece. Custom mouldings are usually undertaken by a specialist audiologist, either at a clinic, or at a workplace health centre. The audiologist will check the condition of the ear before taking the moulding, as excess wax could affect the mould. Where a number of workers require custom mouldings, the audiologist may visit the workplace.

One common approach to providing hearing protection is a dispenser for disposable foam earplugs at the point of entry to a hearing protection zone. The dispenser can act as a reminder to those entering the zone that the protection should be worn, as well as ensuring that the protection is available. Obviously the dispenser must be kept stocked, and the users should be trained in their use.

Alternatives should be provided on an individual basis for workers and others who find disposable plugs unsuitable. Some controlled environments may be incompatible with disposable plugs. In this case issuing protection to individuals who can account for them may be more appropriate. Hearing protection zones, whether recommended or mandatory, should be clearly marked.

Reusable earmuffs fit over the ear and can be used for a variety of ear sizes. Usually two muffs are joined by a sprung headband and the pressure keeps the muffs over the ear. Some people may find the pressure uncomfortable, and spectacle wearers may not be able to seat the muffs properly. A useful feature of earmuffs, however, is that it is apparent that they are being worn. Workers may not be aware that a person is wearing in-ear plugs and may not be able to hear spoken instructions or requests. Earmuffs can also be fitted to protective headgear, which may be more convenient than separate ear protection, although not all headgear will allow this.

Where workers need to communicate or receive instruction, ear defending headsets can be used. The majority of ear defenders are ‘passive’ and rely on the muff or plug blocking the sound. With active noise control a microphone samples the external noise allowing ‘anti-noise’ to be added to cancel out the external noise. Active noise control is normally more effective at low frequencies, but usually there is sufficient passive protection for high frequency noise from the muff or plug.

Active noise control is now increasingly used by air and rail travellers to block transport noise while listening to music. Where employees need to use headsets at work there is also a risk that the communications will in themselves expose the employee above the noise action levels. This is not normally a problem for speech in a normal environment (for example a telephone or call centre operator in a normal office environment) but may be a concern with speech in a noisy environment or where the work involves listening to music. In such cases noise limiting headsets may be used to ensure the signal does not exceed the noise action levels.

What is noise?

This raises the interesting question ‘what is noise?’ Professional musicians obviously do not consider their efforts to be noise, but to a person who does not want to hear the sound from a nearby club or bar, the same music can be noise. In the UK noise was officially described as “any sound which is undesired by the recipient” (Wilson Committee Report on Noise, UK, 1963). This definition is principally concerned with noise nuisance and both the nature of the sound and the sensitivity of the receptor are important factors.

The World Health Organization and European Union consider noise as a pollutant (or in extreme cases a toxin) and noise is assessed on its energy content, so effectively any sound is noise. This is because the research suggests that hearing damage is mainly proportional to the energy in a sound. There is little evidence that, for the same energy levels, different types of sound cause significantly different amounts of hearing damage.

In addition to the variety of styles of hearing protection, it is also important to ensure the correct level of protection is provided. Too little protection clearly does not mitigate the risk of noise exposure, but too much protection may isolate the worker and thus create other risks.

The level of protection is usually defined by ‘assumed protection’; technically this is calculated from the average protection of a number of samples. This allows for manufacturing tolerances as well as differences in fit.

The assumed protection may be presented as a single figure SNR (Single Number Rating) or NRR (Noise Reduction Rating), by high mid and low numbers, or by individual octave band level reduction. Single number values are appropriate where the noise source is broadband and exposure levels are not always at the peak. Where the source is tonal (has a recognisable pitch) or where the exposed person needs to be able to hear surrounding sounds as well as be protected, a more detailed calculation may be required. But the least expensive hearing protection typically provides a reasonable level of safety.

Conclusion

Finally, if a workplace noise risk assessment is carried out it should be reviewed if there is any relevant change in the working conditions. This could be a change in the hours worked, replacement of equipment or rearrangement of the workplace. Sometimes the use of different materials may change the noise levels.

When changes are made, such as replacing worn out plant equipment, opportunities to reduce noise exposure levels below the action levels should be actively considered. If there is any doubt it is much easier to offer hearing protection, which is usually fairly easy to monitor, encourage, and if necessary enforce in use.

Due to the variety of protection available it should be possible to find hearing protection compatible with the activity and other above the neck protection.

Next time you go to a concert, have a look at the drummer or sound engineer’s ears: they will probably be wearing earplugs – they are protecting their ears because they are important. Yours, and your workers’, are too.

Published: 02nd May 2013 in Health and Safety Middle East