Appendix 3: Ear protectors From the Health and Safety Executives reprint of Appendix 4 (Department of Employment Code of Practice 1972) With amendments to paragraphs marked* Permanent re-usable ear plugs 1 These are soft rubber or plastic bungs which are fitted into the ear canal. 2 This type of protector is cheap, but in order to obtain a good seal in the ear canal it is essential that the correct size is used, resulting in a slightly tight fit. Some people require a different size plug in each ear. 3 The most effective types of these plugs are available in a range of 3 to 5 sizes to suit different sizes of ear canal. "Universal fitting" ear plugs are also available, and these have administrative advantages because only one size is needed, but they are not so satisfactory acoustically as properly fitted individualsized ear plugs and tend not to be used properly (they can be retained by the ear with minimal insertion, but then give little protection). All permanent ear plugs, including the 'universal fitting' types, should be initially fitted to the individual by a trained person who should instruct the user on the correct method of inserting the plugs. *4 It is most important that this type of plug is kept clean by regular washing and that they are handled and inserted with hands free of grease, oil, dirt and other particulate matter. Disposable ear plugs *5 These are made from mineral down (or "acoustic wool") which is a special extremely fine glass down with fibres about 1 micron in thickness, or from waxed cotton wool or mastic material, and are intended to be used once only and then thrown away. They can fit any size or shape of ear canal, and provide protection equivalent to good quality permanent ear plugs. Because fresh material is used every time the ear is plugged they may be more hygienic than the permanent ear plugs. Foam plastic ear plugs are available which may be used several times in clean conditions before being thrown away. *6 Waxed cotton wool or mastic material, may be found messy because it must be formed with the fingers before insertion into the ear. The ear canal changes shape slightly with jaw movements and this may cause the plugs to be compressed and lie loose in the ear canal; they should then be extracted, reshaped and reinserted periodically. Neither this operation nor the original insertion should be performed with dirty hands. *7 Mineral down plugs are more resilient than waxed cotton wool or mastic material, and usually retain a good fit provided sufficient material is used to form the plug, and it is folded and inserted in accordance with the makers' instructions. Mineral down is available in packets containing sufficient material for about a week, from dispensers which automatically supply the correct quantity of material, or in packets of pre-formed plugs. Foam plastic ear plugs retain their resilience over several periods of use. 8 Ordinary dry cotton wool is an extremely poor protector and is not recommended. Semi-insert protectors *9 These close the entrance to the ear canal without being inserted into it. One type has soft rubber caps attached to a headband which presses them into the openings of the ear canal. This type of protector has the advantage that, unlike the permanent, reusable ear plugs, one size will fit most people. However to be effective, the headband must press the caps firmly into the openings of the ear canals, and many people will find the pressure intolerable, especially if they must be used for long periods. Another type is moulded from soft rubber or plastic to fit into the outer ear, rather like a hearing aid mould. This type may be made to fit the individual person, using a cold-setting plastic material, and is then very comfortable and effective as an ear protector. * 10 Semi-insert protectors have the advantage that they may be made captive, either by a headband or a cord fitted into the moulded type, which makes them more suitable for use in situations where the loss of an ear plug must be avoided (eg the food industry, etc). As the ear is not covered, these protectors may be more acceptable in a hot environment than ear muffs. They have the advantage of lightness, and may be readily gripped without touching the parts of the protector which come into contact with the skin. They may, therefore, prove more suitable for people who must enter a noisy place for short periods. Ear muffs 11 These are hard cups which fit over the ear and are sealed to the head with soft cushion seals. They have several advantages compared with ear plugs. One size will fit most people, more protection is usually provided, and they are easy to remove and replace - an advantage for people who frequently move from a noisy to a quiet place. It is possible to include ports or valves which can be manually opened during quiet periods, or an electronic device which permits passage of low-intensity signals without attenuation (see paragraphs 16 to 19). However, they tend to make the ears hot, and are bulky so that they are less convenient if slipped around the neck when not in active use. 12 Two types of seal are in general use. A "liquid seal" type comprises a soft annular tube filled with liquid. This type of cushion forms an excellent seal with only slight pressure against the head, but if the tube is damaged due to rough handling the fluid will leak. More robust cushions are filled with soft plastics foam, but some of these need more pressure than the liquid seal type in order to obtain a satisfactory seal. When ear muffs are first issued the user should be asked to check that the cushion is in contact with his head around the entire periphery of the muff. *13 Maintenance of correct pressure on the head is important and the user should be instructed not to reduce the pressure by bending the head band. Modern plastic head bands resist bending and merely snap if overstrained. 14 Some ear muffs are asymmetrical; ie they have one cup intended only for the left ear and another for the right ear. The correct way of wearing these muffs should be prominently marked on them and the user's attention drawn to this matter. 15 All types of ear muffs are liable to be damaged, and it is an advantage if individual parts, especially the seals, can be replaced separately and easily (eg on site or in the factory). *16 Requirements with regard to physical performance and hygiene are detailed in the British Standard BS 6344 Part 1: 1984 "Industrial hearing protectors: Part 1. Specification for ear muffs". The standard also calls for specific wearer information on proper use and maintenance to be supplied with the ear muffs. Information about the attenuation as measured in accordance with BS 5108: 1983 is to be provided to assist in the selection of the most appropriate type of ear muffs (see paragraph 23). Special types of ear protector (a) Amplitude-sensitive protectors 17 There are obvious advantages in protectors which attenuate loud sounds more than quiet ones, and several attempts have been made to develop protectors of this type. 18 Protectors made with small apertures in them usually have rather more attenuation at high sound levels than at low levels due to increased turbulence in the air flow through the apertures at high levels. This effect is used in the 'Gundefender' ear plug developed by the Institute of Naval Medicine for use against gunfire noise (which involves very high levels for short durations). These plugs may be useful for other explosive noises (eg cartridge operated tools), but the evidence available at the time of publishing this Code suggests that they are not suitable for most industrial noises (eg drop forging or fettling) in which the noise is usually more sustained or repetitive than gunfire and in which a high level of continuous noise may also be present, for which insufficient attenuation is given and all communication advantages are lost. 19 Ear muffs are available incorporating an electronic system which will transmit low level sound, but in which a peak limiting circuit stops the electronic transmission of high level sounds so that the basic ear muff then provides the attenuation. These protectors can be extremely valuable in situations in which people are exposed to impulse noise, but must be able to communicate easily during quiet periods between impulses. They are, however, somewhat more expensive than normal types of ear muff, and must be handled with more care. 20 Amplitude-sensitive protectors are difficult to test because the threshold method described in paragraphs 23 to 27 will not measure the attenuation at high sound levels. Ear plugs are particularly difficult to test effectively. It is recommended that these protectors should only be used when the supplier can furnish test data showing the attenuation at the sound levels in which they are to be used. As these data will be in a non standard form, expert assistance is desirable. (b) Frequency-selective ear protectors 21 All protectors attenuate some frequencies more than others, but certain types are especially designed to emphasise this effect. Usually they are designed to attenuate frequencies over about 1,500 Hz but to give only slight attenuation at lower frequencies. If the noise is all at high frequency these protectors can give improved speech communication, but they are unsuitable for most industrial situations which usually involve noise at frequencies less than 1,500 Hz. Testing the performance of ear protectors 22 When purchasing ear protectors the supplier should always be instructed to furnish test data showing the attenuation of sound which will be provided. Because the size and shape of peoples heads and ears varies considerably it is important that the test data should show not only the average attenuation, but also the consistency with which the attenuation is maintained when the protectors are worn by different people. The test data should normally give information on the average attenuation in dB at each of a range of test frequencies and on the scatter likely to occur in practice (see paragraph 26). It is not possible to give an overall figure for the attenuation in terms of sound level dB(A) since the value depends on the frequency distribution in the noise. Guidance on interpreting the data is given in paragraphs 29 to 31. *23 Test data should preferably have been obtained according to the procedure described in British Standard 5108: 1983 (ISO 4869-1981) "Method for measurement of sound attenuation of hearing protectors". (The earlier standard BS 5108: 1974 will continue to be acceptable). Using such test data, it is good practice to obtain the name of the laboratory in which the tests were carried out and details of the standard to which they were tested. Threshold tests *24 Most commercially available ear protectors are tested by a threshold method in which the sound attenuation at each of a range of frequencies is measured. Besides the Standards referred to above several other countries have produced national standards specifying the way in which the test is to be conducted. 25 To carry out the test a person is seated in a quiet room and the minimum sound pressure level which he can hear is found. The person then puts on the ear protection and the increase in sound pressure level needed before the person again hears the sound is taken as a measure of the attenuation provided by the protector. *26 For each frequency to be tested this procedure is repeated on different people in order to test the reliability with which the measured attenuation is maintained. The British Standard procedure requires at least ten subjects for the test. *27 The results of the tests should be presented in tabular form showing the median and upper and lower quartile of the attenuation values, as well as the mean and standard deviation calculated from all attenuation results obtained at each frequency band. Graphical presentation may be employed also. *28 A test at threshold had been accepted by the standards organisations
in several countries as being the best at present available. However it suffers from several serious
problems, including: Calculating the reduction of sound level *29 Suppliers of ear protectors will usually furnish data obtained from
threshold tests described in paragraphs 23 to 28. It should be assumed that the degree of protection
(in decibels) given to most people is equivalent to either: Table 1 illustrates the information provided. *30 In order to calculate the effective reduction in A-weighted sound level, dB(A), a frequency analysis of the noise will be needed; usually this will be an octave band analysis. The assumed protection as in paragraph 29(a) or (b) should be subtracted arithmetically from each octave band level to obtain the assumed octave band levels at the wearer's ear. An example of this procedure is given below. The assumed octave band levels at the wearer's ear should be converted into A-weighted sound level using any convenient method of conversion; a method of conversion is described in Appendix 4. *Example: *31 Ear protectors should normally be specified so that the sound level at the user's ear is always effectively reduced to 85 dB (A) or less. *32 Exceptionally, where exposure is for short periods only, protectors may be chosen so that the assumed value of 32Leq (8) is reduced to 85 dB(A) or less. However, this procedure should be avoided where possible, and if adopted it is particularly important to ensure that the exposure to noise is effectively controlled, and that the ear protectors are correctly used. Hygiene *33 Before any type of ear plug is issued, the user should be asked whether he has ever had any ear troubles such as irritation of the ear canal, or earache and discharging ears, or is under treatment for an ear disease, or is prone to dermatitis or eczema. People with such troubles should be referred to a doctor for an opinion as to whether they may wear ear plugs with safety. 34 Issue of ear plugs should be on an individual basis. If ear muffs are to be transferred from one person to another they should be cleaned before re-issue. *35 Users should be instructed not to insert ear plugs with dirty hands. This is particularly important with waxed cotton wool or mastic material disposable plugs. TABLE 1 Example of the performance of a set of fluid seal ear muffs. The assumed protection is the sound reduction given to the majority of users.
The standard deviation is a measure of the way in which individual test results vary from the mean value. A small value of standard deviation compared with the mean value indicates consistent results. It can be assumed that 50% of test results will be worse than the mean value, 16% will be worse than the mean value minus the standard deviation, and 3% will be worse than the mean value minus twice the standard deviation 2 Median-5O% of test results are worse than this value 3 Physiological noise is audible sound generated in the outer ear. It can readily be heard by covering the ears with the hands. TABLE 2
Total value of I = 0.1533 From Appendix 4 Table 2 A-weighted sound level at the ear is 82 dB(A) (to nearest decibel). return to index |