The importance of Hearing Surveillance at work © First Stop Safety
Most people having a responsibility for managing levels of Noise at work will be familiar with the requirements of the Noise at Work Regulations. They should be able to quote the relevant Action Levels and the duties that have to be undertaken if they are exceeded. They are probably also aware that these Action Levels are going to change in February 2006 as the new Physical Agents (Noise) Directive takes effect in the UK. However, a grasp of what lies behind the Action Levels will lead to a better understanding of the regulations and improved protection of the hearing of employees.
First of all it is instructive to consider the origin of these Action Levels. They are based on masses of statistics of hearing loss suffered compared with noise levels that people have been exposed to. These statistics have been collected over a long period of time since Noise Induced Hearing Loss is a long-latent disease. The Action Levels are set so that the majority of people will suffer only moderate levels of hearing loss. There is no such thing as a safe level of exposure. What one would appreciate immediately from this is that even if the noise exposure of an employee is below the First Action level, there is still a risk of hearing damage.
The move to the new Directive is prompted by concerns that the current regulations present an unacceptable risk to hearing. These new limits are called Action Values and are not based on new data on hearing loss. They are merely aimed at reducing the percentage of people that are likely to be affected by Noise Induced Hearing Loss (NIHL).
Some companies spend a lot of time and effort in producing noise surveys that show exposure levels at just below Action Levels. This can be done say by reducing the time spent by employees in noisy locations. However, as we have seen above this does not mean that those employees are safe from any hearing damage.
Having looked at the background to the Action Levels/Values, we can look briefly at the tasks facing us if these are exceeded. For those familiar with the regulations, these include the provision and use of hearing protectors, reduction of machinery noise at source and the marking out of Hearing Protection Zones. Assuming that one is putting into practise all the requirements of the current regulations, there are a number of issues that should still concern us.
· What about the hearing of staff that join the company with a pre-existing condition? As the effects of Noise Induced Hearing Loss take a long time to become a serious problem, one needs to make sure not to take on responsibility for hearing damage that may have occurred during a previous employment.
· As we have seen, the Action Levels are based on statistics, and keeping exposure below these can still result in some employees suffering hearing damage over a long term. It is important to have a way of identifying more susceptible individuals.
· Having provided hearing protectors where necessary, there is no easy way to check that these are effective, or are being worn at all. How does one make sure of this?
Hearing surveillance provides us with a way of addressing all these issues. It allows us to establish a base line for new employees. We can use this data as a benchmark to check whether this deteriorates with the current employment. It allows us to monitor all staff and identify more susceptible persons. Once highlighted, these personnel can be moved to other tasks with lower exposure levels. Finally, hearing surveillance monitors the effectiveness of the protection provided.
What are the different methods of surveillance available to us? Many of the larger companies tend to own an Audiometer with suitably trained personnel to operate it. This is an ideal solution, albeit costly for smaller companies. There is the cost of the Audiometer to start with and associated training costs in having someone familiar with the use of it as well as being able to interpret the results.
The alternative method of using a mobile Audiologist may suit some. This service is mainly provided by NHS qualified Audiologists. For the smaller company, use of a hearing aid Audiologist may also be an option. A quick look at the Yellow Pages will identify them in most towns and cities and most will be happy to carry out a test to assess hearing levels at their premises.
Whichever method is used, the process of checking the hearing is very similar. A range of tones at different frequencies and levels is played to the subject through a set of headphones. Whenever the subject hears a tone, they acknowledge this by pressing a button. By this means, the Audiologist determines the hearing threshold for the person. Figure 1 below shows a typical Audiogram for someone suffering from NIHL.
In addition to this basic test, the Audiologist will examine the ear canal and carry out additional tests if required. All these are usually carried out in a sound proofed booth, as some of the sound levels are quite low and general background noise may affect the results.
Picture shows an ear being examined (Otoscopy) prior to a hearing test.
(c) Shout Pictures/Medical-On-Line
The hearing threshold range will vary depending on the age and sex of the subject. If the measured hearing level is outside of this, then the contribution to this loss due to noise exposure at work has to be considered and appropriate action taken. The HSE provide advice on this in their document MS26: “A guide to audiometric testing programmes”.
A recent innovation to hearing surveillance at work is the use of Screening Audiometers or “hearing checkers”. These simple to use devices check hearing only at one or two frequencies. They can be used to separate employees with hearing in the appropriate range from those that are outside this. A substantial reduction in the cost of hearing surveillance can be realised by the use of hearing checkers, as only a small number of people need to be seen by an Audiologist.
As all Audiometry is dependent on some feedback from the person being tested, they are susceptible to falsification. It is possible for someone to pretend that his or her hearing is worse than it is by not pressing the button, even when a tone can be clearly heard. However, professional Audiologists are trained in detecting this and have ways of double-checking results. If someone falsifies the results when a hearing checker is being used, then they would be referred to an Audiologist anyway and would then find it impossible to repeat their previous results. With any type of Audiometer, it is very difficult to falsify results to show ones hearing as being better than it really is.
Another innovation in checking for Noise Induced Hearing Loss is the use of Otoacoustic emissions. These are emissions from the outer hair cells of the inner ear in response to transient stimulus applied at the ear. These emissions are absent if there has been damage to the outer hair cells due to excessive noise exposure. Whilst this technology holds great promise in that it is not possible to falsify results, the equipment is currently many times the cost of conventional Audiometers.
In summary, hearing surveillance provides us with a number of benefits in the workplace.
· It allows us to check the hearing of new members of staff and avoid accepting any liability for hearing damage due to past employment.
· Employees who are more susceptible to NIHL can be identified and protected.
· Provide a safety net in checking that hearing protectors are being used and are proving effective.
T. Segaran
2nd February 2005
First Stop Safety
First Stop Safety supply test instrumentation to help with the maintenance of a safe workplace. They supply PAT testers, Sound Level meters and Light meters. A device aimed at checking hearing levels is scheduled to be launched later in 2005.
Bibliography
HSE CRR 2/1988: Tables for the estimation of hearing impairment due to noise for otologically normal persons and for typical unscreened population, as a function of age and duration of exposure.
HSE Guidance Note MS26: A guide to audiometric testing programmes.
Managing Noise and Vibration at work, by Tim South
Balantyne’s Deafness (6th edition), Edited by John Graham & Mike Martin
Principles of Hearing Aid Audiology (2nd edition), by Maryanne Tate Maltby
