A four stage hearing protection plan

Long-term and repeated exposure to harmful levels of noise can result in chronic health effects, known as Noise Induced Hearing Loss (NIHL). Providing employees with protection from noise hazards in the workplace is a legal requirement. Sarah Broadbent, from the Personal Safety Division of 3M, looks at a four-stage programme to help employers understand and implement an effective hearing conservation strategy, covering the identification of potential noise hazards and selection of appropriate hearing protection equipment (HPE), as well as hearing protection validation and training for employees.

 

Excessive and repeated noise exposure can lead to NIHL, which has serious and long-term effects: it is permanent and cannot be reversed. Worryingly, it is not always possible to tell whether a sound in the workplace is excessively loud and, often, harmful sounds tend to not feel as if they are causing damage at the time of exposure. 

 

When workers are exposed to potential risks in the workplace, a hierarchy of control measures should be followed. When considering noise hazards in the workplace the first step is to identify whether the source of noise can be reduced or eliminated by altering the process or equipment being used. If this is not possible, the next step is the introduction of engineering controls to reduce noise at its source or prevent its transmission. The final recourse is to introduce personal protective equipment (PPE), in this case hearing protective equipment.

Where noise levels exceed 80dB(A) hearing protection must be provided and at levels above 85dB(A) wearing it must be strictly enforced. The Control of Noise at Work Regulations (2005) state that the employer shall "assess and measure the levels of noise to which workers are exposed”. A simple noise indicator can be used to identify noise levels or for advanced measurements a more sophisticated sound level meter or dosimeter can be used.

 

Sound level meters, such as the 3M Sound Detector SD-200, are relatively simple and can be used to indicate areas with high noise levels. Other meters, for example the SoundPro Sound Level Meters from 3M, are more sophisticated and are used during formal noise surveys. Dosimeters, such as the Edge Sound Level Meter from 3M, are designed for personal noise monitoring, to measure the exposure of individuals, and are worn by the worker to provide an accurate reflection of the noise levels they experience.

HPE is designed to help reduce noise to a safe level, termed attenuation, and it is important to ensure that the correct level of attenuation is achieved. Under-attenuation leaves the wearer still exposed to noise risk, whilst over-attenuation could block out too much sound, leaving the wearer isolated from their environment or unable to hear warning signals.  It is also essential to recognise and understand that different occupational noise hazards and environments will require different types of hearing protection.

 

The attenuation of hearing protection can vary greatly with noise frequency and the overall effectiveness of a particular ear protection product depends on the frequency content of the incident noise.

 

There are three main methods that can be used to calculate the sound pressure levels at the ear when wearing hearing protection: octave band analysis, the High, Medium, Low (HML) method and the Single Number Rating (SNR) method.

 

Octave band analysis is the most accurate method based on octave band measurements of the sound pressure level of the noise. This will result in an accurate assessment of the noise at the user’s ear. The HML method requires measurement of the A-weighted (LA) and C-weighted (LC) sound pressure levels.  The HML values supplied by the ear protection manufacturer can be used to estimate the protection required. The SNR method requires measurement of the C-weighted (LC) sound pressure level. The effective A weighted sound pressure level at the ear is given by subtracting the SNR value, taken from the manufacturer’s data, from the LC value (LA = LC – SNR).

 

It is important to consider compatibility with other forms of personal protection equipment. If equipment such as a safety helmet or safety eyewear is also needed, the items must work together as a whole, otherwise there is always a danger that one piece might compromise the performance of another. This can also impact on comfort and, above all, the chosen HPE should be comfortable to ensure that the wearer keeps it on at all times when it is needed.

Under the Regulations, employers are required to provide employees with information, instruction and training. The principal need is to ensure that workers fully understand the health implications if they fail to use and maintain their HPE correctly.  They need to understand the level of risk that they may be exposed to, how it is caused and the possible effects and consequences.

 

It is crucial to communicate to employees that only 100 per cent compliance will achieve full protection. If workers remove HPE for even a small amount of the time they are exposed to harmful noise, the level of protection will be significantly reduced. Wearing HPE for only 90 per cent of the time, for example, will mean that the wearer is offered virtually no protection.

The Regulations state that the use of HPE must be strictly enforced at levels above 85dB(A), but it can be difficult to determine what levels of protection it is offering the wearer without validation testing. We have already discussed the different methods used to describe levels of attenuation, but these can vary greatly with noise frequency. The overall effectiveness of HPE depends on the frequency content of the incident noise, if the HPE is not correctly fitted, then a lower level of protection will be achieved.

 

For these reasons, it is recommended that a ‘real world’ factor of 4dB(A) be applied, meaning that when calculating the actual protection level offered by HPE, 4dB(A) should be deducted from the manufacturer’s own predicted attenuation figure (SNR).  Even when this is applied, a number of other factors need to be considered, making validation testing necessary.

 

HPE validation is not a legal requirement, but should be regarded as best practice. The E-A-Rfit Validation System from 3M, for example, enables employers to help inform employees of the effectiveness of fitting an earplug. The system objectively validates the personal protection levels for each worker, using a specially probed version of 3M earplugs to generate an individual Personal Attenuation Rating (PAR). This, in turn, gives an indication of the effectiveness of the HPE for that individual.  Ratings can be quickly and easily compared across different products to determine best fit. Further quantitative data can also be generated to analyse sound pressure inside ear canals, resulting in accurate and personalised results that do not simply rely on user feedback.

 

Speak to experts from 3M about Hearing Protection and more on Stand 76 at Health & Safety North.