The Selection of Hearing Protection
There are many aspects to noise within the workplace, from conducting a risk assessment to noise control measures, but at some point within the process it is likely that it will be necessary to issue Personal Protective Equipment (PPE) to at least some employees.
A noise survey will determine just who needs ear protection. The survey should list employees and their exposure, not a map of the factory, then compare their exposure to the relevant action levels to determine who needs to wear the protection.
There are two main types of exposure that need to be measured or calculated: the LEX,8h, which is the daily noise exposure (or average over a week if daily variation in exposure occurs) and LCpeak, which addresses protection from instantaneous damage to hearing when the peak noise is measured. The action levels have acceptable values for both these parameters. Note that within the UK, the LEX,8h is known as the LEP,d, but they both have the same meaning. A good quality sound level meter or dose meter will be able to calculate these values, but care must be taken with the LEX,8h to ensure that the correct exposure time for the noise is inserted into the instrument, taking into account work patterns and breaks. A brief summary of when hearing protection needs to be worn relative to these action levels is:
Below the first action levels
Below an LEX,8h of 80dB(A) or LCpeak of 135dB(C) hearing protection does not have to be worn.
Between the first and second action levels
With an LEX,8h of between 80dB(A) and 85dB(A) and an LCpeak of 135dB(C) and 137dB(C) hearing protection should be made available to employees who ask for it but it is not compulsory to wear.
Above the second action levels
With and LEX,8h over 85dB(A) or an LCpeak of 137dB(C) employees must wear the hearing protection provided and employers will need to provide training on correct use.
The EU directive also introduces the concept of exposure limit values at the ear, taking into account the attenuation of the hearing protection, which cannot be exceeded. The exposure limit values correspond to an LEX,8h of 87dB(A) or an LCpeak of 140dB(C).
Selecting the correct hearing protection is essential. There are many factors to be considered – chiefly the fact that any PPE is only effective if it is worn.
The same is true of hearing protection. There is no point buying the most expensive ear muff that attenuates the noise by, say, 30dB(A) if the employee has to remove the muffs for two hours of an eight hour shift because they are uncomfortable. That will only reduce the daily noise exposure by 6dB(A) instead of 30dB(A).
There are three main types of protection: earplugs, earmuffs and semi-inserts, each with individual benefits, and there are many factors affecting their choice.
Use with other PPE
The interaction of hearing protection with other PPE that may need to be worn is an important factor. An employee wearing prescription or safety glasses will not obtain an adequate fit from a standard ear muff, so plugs or perhaps semi-inserts become the better option – although special glasses with a flat side to obtain a better fit are available, should earmuffs be necessary.
The use of hardhats with earmuffs can still be an issue. If the employee constantly needs to wear them both together a hard hat with built in hearing defenders should be considered. However, this may not be the best option because this type of hearing muff does not give quite the same protection as regular hearing muffs.
Communication can be a big issue with PPE and it all comes down to the attenuation that the protector will provide. If a protector is provided with too little attenuation, not enough protection will be given. To go to the other extreme, however, simply ‘buying the best’ and providing too much attenuation generates associated issues.
Too much reduction of the noise can instil a feeling of isolation that is detrimental, as employees may need to remove their PPE in order to communicate with colleagues. The subsequent exposure to noise will therefore far outweigh the benefits a high attenuation hearing protector would have provided.
Another major problem with over attenuation of a hearing protector is that of safety. There is an inherent danger in providing too much protection because of listening out for safety warnings such as fire alarms and sirens from reversing vehicles. A general rule of thumb is to not provide so much protection as to reduce the level at the ear to below 70dB(A) as this would be over protection, but aim for a level of 75-80dB(A) at the ear. See below for how to calculate the noise levels at the ear after taking into account the hearing protection.
The environment and individual
Other individual preferences such as hair and jewellery affect the choice of hearing protection. Long hair that flows over the ears will cause an inadequate fit of an earmuff and hence a significant education in the effectiveness of the protection, while earrings will cause a comfort problem, so plugs or semi inserts are an alternative.
The working environment also has an effect on the choice of protector: hot humid conditions make earmuffs uncomfortable to wear, while dusty environments cause problems with hygiene, especially with plugs. In this case it is especially important to keep the hands clean when inserting the plugs as they could cause an ear infection. It is advisable to ascertain from an employee any history of ear problems such as irritation or earache, in which case the use of earmuffs that fit over the outer ear is preferable.
The predicted attenuation
This is where we enter into the ‘dreaded’ world of logarithms. There are three methods for predicting the overall attenuation that a hearing protector will give, and each rises slightly in the amount of mathematics required.
The methods for calculating the effectiveness of hearing protection are:
• Octave band
In terms of accuracy in predicting the attenuation, the SNR method is the least accurate and the octave band is the most accurate, and hence is the preferred method. However, it does require a little more calculation.