Published: 10th Sep 2007
The truth, the whole truth and nothing but the truth
Hearing protection is your final stop on the journey to control workplace noise and prevent people losing or damaging their hearing. Only when practical and managerial controls to reduce the intensity and duration of noise exposure have been exhausted should you consider hearing protection as anything more than a temporary measure.
The EU Physical Agents Directive requires hearing protection to be made available by the employer for those people exposed above a daily average of 80dB(A) and wearing protection is mandatory once a person’s daily exposure reaches or exceeds 85dB(A).
Hearing protection should be selected according to the level and character of the noise so that exposure is reduced to a safe level. Hearing protectors come with data, which can be used to estimate the protection they will provide. This is obtained from laboratory tests on a group of real people. Their threshold of hearing (level of the quietest sounds they can hear) is recorded for a range of frequencies. The difference in threshold with and without the hearing protector worn is taken as the attenuation. The group mean attenuation minus the standard deviation is the assumed protection used to estimate the protection given in the real world.
But in the real world the attenuation can be very different to that predicted by this standard test. The effectiveness of hearing protection is reduced by general deterioration of the protector with use, less than perfect fitting, and the interference of other head-worn PPE. And of course there is also the problem of ensuring it is worn. Choosing high attenuation protectors is not a solution because hearing protection can also create problems; making communication difficult and reducing the audibility of alarms and other danger signals. For this reason we also have to be careful not to overprotect.
Over the spring and summer of this year the Health and Safety Laboratory investigated how well hearing protection is really performing. This included visiting noisy workplaces to observe real world use and laboratory measurements of protector attenuation when worn in real world ways.
So here it is - the truth about hearing protection.
Laboratory tests on earmuffs
Earmuffs use cups to provide a barrier to the sound. The cups are lined with a sound absorber (usually foam), and held firmly against the ears by a tensioned band. The seal around the edge of the cup is designed to ensure there are no gaps between the cup and the head.
Eight models of new earmuffs were tested; from lightweight low attenuation earmuffs to heavy-duty high attenuation earmuffs. These earmuffs are listed in Table 1 with the standard test SNR (single number rating) value provided by the manufacturer of the earmuff and the cost. The SNR is a measure of the earmuff attenuation in dB. When subtracted from the C-weighted level of the sound it gives an estimate of the A-weighted level at the ear of the wearer.
|1. Lightweight, multi position plastic band||23||£4|
|2. Lightweight, multi position plastic band||28||£5|
|3. Lightweight, multi position plastic band with optional head strap||30||£7|
|4. Midweight, multi position plastic band with optional head strap||30||£10|
|5. Midweight, wire type band fixed in over head orientation||31||£12|
|6. Midweight, wire type band fixed in behind neck orientation||31||£12|
|7. Midweight, helmet mounted||30||£13|
|8. Heavyweight, wire type band fixed in over head orientation||35||£14|
Four subjects were used to test the range of earmuffs. The subjects were seated in a diffuse field of random noise. The sound level in both ears was measured with and without the earmuffs using a miniature microphone in the ear. The difference gave the earmuff attenuation from which the actual SNR achieved was calculated. Unlike a standard test where the test subjects are asked to ensure they have achieved the best fit they can, our subjects were just asked to fit the earmuff as they would normally. Earmuffs were worn with and without other PPE in their new condition, and in artificially aged, and damaged conditions without PPE.
Earmuffs and other PPE
When other head worn PPE is used with hearing protection it can prevent a proper seal between the face and the cup. There may also be problems fitting the headband over the PPE so the cups are secure.
New earmuffs were tested with and without other head worn PPE. Where no PPE was used the earmuffs were worn with the headband in the overhead orientation except for earmuff 6, which could only be worn with the band around the neck. When worn with other PPE the best orientation of the earmuff headband was left to the test subject’s discretion.
Muffs 3 and 4 were tested with and without their optional fabric head strap when worn with the hard hat.
The results of the attenuation tests with and without PPE are given in Table 2.
|Muff||No PPE||Hood||Beanie hat||Helmet||Safety glasses||Small goggles||Large goggles||Visor||Dust mask|
|4 + strap||14−30||13−16||14−19||13−18|
Important points from Table 2:
- Earmuffs can give far lower protection than predicted from supplied data, even when worn without other PPE
- Selecting a higher attenuation earmuff does not necessarily give the wearer increased protection; good fitting is a more important factor
- Attenuation is always limited when earmuff cups are placed over clothing
- Earmuffs can give a highly variable attenuation when worn with PPE that goes under the earmuff seal or alters the fit of the headband
- There is a need to visually check an adequate fit has been achieved. Reliance on the attenuation rating alone is not enough
|Muff||New over head||New around neck||Aged over head||Aged around neck||Damaged seal over head||Damaged seal around neck||Stretched head band over head||Stretched head band around neck|
|1||18−21||18−20||12−18||7−17||15−20||12−19||No test||No test|
|2||18−25||17−24||8−19||3−18||15−19||7−18||No test||No test|
|3 + strap||21−27||11−27 15 - 30||11−22||6−13||20−29||18−26||No test||No test|
|4 +strap||14−30||12−27 24−30||13−26||9−19||18−30||7−24||No test||No test|
|6||No test||15−30||No test||19−30||No test||11−26||No test||4−28|
|7||15−29||No test||15−26||No test||12−27||No test||12−28||No test|
Wear and tear, and orientation of earmuff
Normal wear and tear reduces the effectiveness of earmuffs. Headband tension slackens over time and seals deteriorate with use. New samples of the earmuffs were subjected one of three ageing or damaging treatments before testing to see how this altered the attenuation.
- Simulated ageing by placing earmuffs in a temperature of 40°C, under tension, for a week. The photographs below show untreated new test earmuffs on the left, artificially aged earmuffs on the right. You can see how this has slackened the headband tension of earmuffs 1 to 4 (first three on first row, centre on second are now more spread). Earmuffs 5, 6 and 8 with the wire bands seem unaffected
- Simulating seal damage by slitting the seal and removing about an eighth of the inside foam as shown in the photograph above. The additional liquid seal in earmuffs 5, 6 and 7 was also cut
- Stretching of the wire headbands of earmuffs 5 to 8 by holding them flat for one minute
As earmuff attenuation can vary according to how the headband is worn measurements were made with the headband over the head and behind the neck.
The ranges of measured SNR values for earmuffs treated and worn as above are shown in Table 3.
Important points from Table 3:
- The reduced headband tension caused by ageing gives a significant loss of attenuation without obvious visual damage
- Metal wire reinforced bands (as on muffs 5 to 8) were less susceptible to stretching and loss of tension
- A damaged seal will reduce attenuation. However, it is likely this will be easily spotted before it is too significant
- Multi-position earmuffs generally give a better fit when worn over the head rather than with the band behind the head or around the neck
- Mid to heavy weight earmuffs need to be worn with a supporting head strap when not worn in the overhead position
|1 Banded tapered earplug||19||£4|
|2 Corded premoulded flange earplug||20||£2|
|3 Banded round earplug||23||£3|
|4 Premoulded bulb shape earplug||28||30p|
|5 Compressible foam earplug||28||20p|
|6 Foam earplug on stalk||28||50p|
|7 Premoulded flange earplug||35||£1|
|8 Compressible foam earplug||37||20p|
Laboratory tests on earplugs
Earplug performance depends firstly on how well the user fits the earplugs; the nominal attenuation rating is secondary. Measurements were made to compare how the attenuation varied with different methods of fitting and insertion depth, across a range of earplugs. Table 4 shows the range of earplugs tested.
Measurements were made of the sound level in a diffuse field of random noise at the eardrum of a simulated ear on a KEMAR (Knowles Electronics Manikin for Acoustic Research) head and torso simulator. The difference in level with and without earplugs fitted was recorded as the attenuation. The attenuation obtained with a simulator cannot be compared directly to the performance on human subjects so no SNR values have been taken from these results. Instead the test enabled identification of when the earplug was well fitted and providing its optimum attenuation and when not. The results are in Table 5 under the following classification.
- Best indicates the highest attenuation obtained for the earplug
- Less indicates lower attenuation overall but significant attenuation still at both high and low frequencies
- Negligible indicates no protection at and below 500Hz (protectors may provide some protection at high frequencies)
Important points from Table 4:
- To achieve the full attenuation, premoulded plugs should be inserted to the full intended insertion depth
- Foam plugs should be rolled so they expand fully in the ear canal. When folded or squashed they give virtually no protection even if deeply inserted
- Banded plugs must still be inserted into the ear canal. Plugs held only against the canal entrance by the band give virtually no protection
Hearing protection use in the workplace
So outside the laboratory how well are people really using hearing protection? In the following section there are legal requirements and accepted guidelines, together with some good and bad practice seen when visiting workplaces.
Selection of the right protectors
- Under European regulations, protectors should be chosen so as to eliminate or minimise risks to hearing
- Hearing protection should be issued after consultation with employees or their representatives
- Hearing protectors should reduce peoples’ daily exposure to below 85dB(A)
- Hearing protectors that reduce the level of the noise at the ear below 70dB(A) should be avoided as they impose an unnecessary hearing impairment
- Provide a choice of suitable protectors so each person can choose those they find most comfortable
- Visually check each person can achieve good fit of their chosen protectors; earmuffs fitting closely to the head with no gaps, plugs well inserted
Good practice in the real world
- Earmuffs are the preferred choice for intermittent use as they can be readily be removed and refitted
- Most workplaces visited provided a choice of protector. Generally two choices of earmuff and two choices of earplug were offered although in some places only earplugs were allowed for hygiene reasons
- Two factories visited were using custom moulded earplugs. These were considered to give the best fit and to be the most comfortable of all earplugs especially when working in high temperatures
- Sound restoration protectors that use electronics to restore or amplify the outside sound in low noise levels are normally only used in quiet environments with intermittent very high-level noise such as gunfire. In one workplace these were tried as a protector for a hearing aid user. The aid malfunctioned under earmuffs but the sound restoration earmuffs assisted hearing in low levels and provided attenuation in high levels
- At least half of all workplaces visited were over protecting by selecting highest attenuation protectors regardless of the level of the noise
- A significant minority of workplaces provided only one choice of protector
- One workplace had imposed hearing protection without consultation or assessing what risk existed and what attenuation was required. There was no indication of where and when hearing protections should be used. Workers there were clearly confused as to when hearing protection was required
Using hearing protection with other PPE
- Integral PPE combinations are the best choice where multiple PPE is used
- Helmet, visor and earmuff combinations were used almost universally with strimmers, hedge cutters, and in forestry. Helmet users were also generally using integral PPE
- Where integral PPE combinations are not available earplugs are widely used with other PPE rather than earmuffs
- Outdoor workers were successfully using baseball style caps that could be worn without interfering with the fit of their earmuffs
- This gentleman was using a road breaker. His colleague was using a cut off saw and his earmuffs were worn over goggles, hat and jacket hood. I will say no more
- Where integral PPE combinations are not available earplugs are widely used with other
Care and maintenance of PPE
- Have replacement hearing protection readily available and safe places to store reusable protectors
- Keep a record detailing the issue of hearing protectors and ensure users know what to do when they have problems with their protectors
- Check the headband tension by comparing the separation of the earmuff cups when off the head with a new pair of the same earmuffs
- One really on-the-ball employer required employees to check the condition of their protectors every month. Records were kept on when new PPE was last issued. New earmuffs were held in stock and available any time. Earmuffs were labelled with the users name, and users had a safe place to keep them
- Most places using disposable earplugs had dispensers available at all entrances to the noisy areas. One brilliant workplace had handwashing facilities by the dispensers so plugs could be fitted with clean hands
- A workplace using custom moulded earplugs had an annual test and service of the earplugs by the earplug supplier
|Earplug||Fitting/ compression||Deep insertion||Halfway insertion||Edge of canal|
|5 and 8 Foam||Rolled whole length||Best||Best||Less to Negligible|
|5 and 8 Foam||Folding along length or squashing||Negligible||Negligible||Negligible|
|6 Foam on stalk||Pushed into canal||Best||Less||Less to Negligible|
|4 Premoulded bulb||Pushed into canal||Best||Less||Less to Negligible|
|7 Flanged earplug (high attenuation)||Pushed into canal||Best||Less||Negligible|
|2 Flanged earplug (low attenuation)||Pushed into canal||Best||Best||Negligible|
|1 and 3 Banded earplugs||Earplugs pushed into canal||Best||Best||Best|
|1 and 3 Banded earplugs||Earplugs only held against canal by tensioned band||Negligible||Negligible||Negligible|
- These earmuffs were in use at a small woodworking factory. The headband had broken from the cup and was refitted with wood glue allowing no movement between the cup and band. The seal was also damaged. No replacement earmuffs were available
- Some earmuffs seen were very dirty. Dirt can reduce the attenuation because it discourages proper fitting of the protector
Training and information
- It is a legal requirement to provide training and information when hearing protection is required
- Hands-on training was provided for new recruits and when new protection was introduced in some companies. Small businesses were using external specialist trainers; some larger businesses were able to provide in house training
- A significant proportion of workplaces were providing protectors with no training
- One employer only provided written safety information even though he had no expectation it would be read or understood
- In some workplaces there were no clear instructions as to when and where hearing protection was required
Fitting and wearing hearing protection
- Cover your ears with your hands to check the fit of your earplugs. If the sound changes the earplugs are not fitted properly
- When fitting earplugs pull back on the pinna (the outer ear) as you insert the earplug. This straightens out the first kinks in the ear canal and allows the earplug to go in more easily
- Try to fit the earmuff cups tightly against the side of the head. Adjust the headband to give a reasonably firm fit
- Use a head strap to support heavy earmuffs worn with a neckband
- Companies with good hearing protection use had systems in place to check proper use on a daily basis
- Foam earplugs are the most commonly used type. In most cases the plug is compressed incorrectly or not at all before fitting.
- In a large woodworking factory noise levels were generally between 90 and 100dB(A). One preferred type of earplug was commonly worn wedged across the hollow of the pinna (outer ear) rather than in the ear canal. These would have provided no protection at all. No training had been provided on fitting the hearing protection
- Earmuffs are often worn with the headband around the back of the head even when they are only intended for wearing over the head
Are there employers out there who have yet to consider noise control in place of hearing protection? About a third of the noisy workplaces visited had not considered noise controls. Some employers still think hearing protection is an easy and effective solution. If you think that please think again.
For more information on hearing protection visit http://www.osedirectory.com/product.php?type=health&product_id=6
Published: 10th Sep 2007 in Health and Safety International