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|Year : 2011
: 13 | Issue : 51 | Page
|A qualitative assessment of the performance of electronic, level-dependent earmuffs when used on firing ranges
National Acoustic Laboratories, Chatswood, NSW, Australia
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|Date of Web Publication||1-Mar-2011|
A qualitative workplace trial was undertaken to examine the performance of sound restoration, level-dependent electronic hearing protectors (HPs) in a high impulsive noise environment using participants who were very experienced in the regular use of passive HPs. The results indicate that this type of HP is well accepted by experienced users, particularly so, by those who appreciate reliable communication while wearing the devices.
Keywords: Electronic hearing protectors, hearing loss, impulse noise, noise exposure, shooting
|How to cite this article:|
Williams W. A qualitative assessment of the performance of electronic, level-dependent earmuffs when used on firing ranges. Noise Health 2011;13:189-94
| Introduction|| |
In the hierarchy of noise exposure management, the use of hearing protectors (HPs) falls low on the list, and as with any risk management approach, the elimination of the hazard is always preferable to a situation of "protected exposure" ,, . However, there are noisy situations where the use of personal protective equipments (PPE) such as HPs offers the only practical solution such as on weapon firing ranges. In practice, while the PPE attenuates the offending noise, it also impedes communication and limits user awareness of their immediate surroundings. Reasons proffered for the non or limited use of HPs regularly include lack of communication and lack of awareness of the immediate environment. 
Modern level-dependent HPs are currently commercially available which specifically include features for communications and an ability to be aware of surrounding environmental conditions. These level-dependent HPs facilitate the passage of sound, below a specific preselected level, through the use of electronic circuitry. When the sound level rises above the preselected level, sound transmission is terminated and the passive attenuation of the HP acts so as to reduce the level of the wearer's exposure. In this way, the wearer can listen to nearby conversation, environmental or background noises while the overall sound levels are low but have their hearing protected when sudden loud noises unexpectedly occur.
Communications are facilitated via a direct connection of the HP to two-way mobile radios and/or BlueTooth® type connections to cell phones by utilizing a separate "speech microphone" and associated electronic circuitry and signal processing. This circuit processing has the ability to discriminate speech from unwanted environmental noise for clearer communications. Thus, the wearer can experience good radio and mobile telephone communications, awareness of local environmental noise and face-to-face conversation while being protected from unwanted, loud, damaging sounds.
Casali and Robinson  presented a summary of the performance and technology, covering the principles and performance of level-dependent and sound transmission devices. However, this was a summary of objective measures and did not include subjective measures from device users. There appears to be very little in the way of independent, subjective studies conducted with users of level-dependent HPs. A subjective study  found advantages with the use of active level-dependent HPs when compared to passive protectors for exposure to continuous noise in the engine rooms of Singaporean navy ships. However, most device performance information comes primarily from manufacturers' claims and word-of-mouth from distributors and early adopters.
This particular research project was prompted by a desire to examine performance claims in realistic working situations and to determine if such improvements in features and performance can promote more consistent and better HP use in high risk situations.
| Methods|| |
Devices under test
Three models of HPs were issued for use over a 3-month trial period. Model 1 consisted of a level-dependent, sound restoration product with the external sound input limited to 82 dB and separately adjustable amplification to left and right ears. Model 2 was similar to Model 1 except that it was constructed with a low profile so that it could fit underneath a protective, military style helmet. Model 3 was again similar to Model 1 but with the additional feature of Bluetooth® connectivity to other Bluetooth® devices.
The participants in this survey were 15 very experienced trainers/instructors (2 females, 12 males and one undeclared) who regularly work at indoor and outdoor firing ranges instructing novice shooters and re-assessing experienced shooters in weapon handling, safety and accuracy of use. Their mean age was 39.7 years (SD = 6.9) with a range of 29-56 years. The ratio of female to male participants is a reflection of the make-up of the particular workplace and was not introduced through any artificial biased sampling method.
The devices were tested primarily at an indoor firing range with some use at an outdoor range. The outdoor range essentially provides free field conditions with minimal reflections and open exposure to weapons' fire from other shooters simultaneously using the area. The majority of the assessment was carried out at indoor ranges with high reverberation. There is some isolation provided by small dividing walls between shooter positions, but instructors are usually exposed simultaneously in a direct line to multiple shooters with minimum attenuation. Depending upon the position, the peak levels (L Cpeak ) do vary somewhat but are well above the exposure level of 140 dB for both indoors and outdoors. During a typical work day, instructors can be exposed up to several hundred shots per day. Students are required to wear standard passive hearing protection consisting of a combination of plugs and muffs.
Background noise levels arise primarily from people attending the ranges and can vary significantly depending on the number of individuals present at any one time. However, they remain well below defined hazardous exposure levels.
A survey tool, comprising two main parts and compiled from previously validated and new questionnaires, was used for this work. The first section of the questionnaire asked for demographic details and self-reported information on hearing health.  The second part of the questionnaire requested information on current HP use and usability, along with opinions and attitudes toward HP use. Some open-ended questions were included with the aim of eliciting information that may not otherwise have been covered by closed questions.
The third part consisted of a set of 16 questions relating to the use and wearing of the specific HPs in use during the trial. For variety, the questions were framed in both a positive and negative manner and scored on a 5-point Likert scale with "1" representing a definite "no" and "5" a definite "yes". This section of the questionnaire was piloted with several users before this specific work to ensure that the questions were clear in meaning and intent, but was otherwise specific to this work.
A copy of the questionnaire is included as an Appendix [Additional file 1] to this manuscript. Ethical approval for the project was provided by the Australian Hearing Human Research Ethics Committee. The questionnaire was requested to be completed by each participant at the end of the trial period.
| Results|| |
Self-reported hearing loss
As there was no opportunity to carry out a pure tone audiometric hearing test on participants, it was felt that the four questions used as a self-reported test would provide an indication of participants' current hearing health.  The first three questions and respective positive responses were:
Four participants responded "yes" to all three questions, and one to two questions. Previous research  indicates that a positive response to the first question "Do you think you have a hearing loss?" or a positive response to any two of the three questions provides an indication of an actual hearing loss with a specificity of 75%. These results indicate that seven of the 15 participants have a high probability of a measurable hearing loss. Five participants indicated that they experienced tinnitus.
- Do you think you have a hearing loss? 7 yes
- Do family or close friends ever say they think you have a hearing loss? 6 yes
- Do you have trouble hearing conversation in background noise? 5 yes
While some respondents indicated that they sometimes experience difficulties hearing, their hearing status was accepted as meeting the requirements of their employer as tested during regular health assessments.
Current and trial HP use
HPs are worn for the whole of the exposure time to noise above the maximum regulation exposure level of (L Cpeak ) 140 dB, as required by strictly enforced workplace occupational health and safety practices. The trial HPs were worn for the whole of any exposure time.
Responses on current HP use indicated that they were currently used for 3.5 hours (6), 2.5 hours (8) or 1.5 hours (1) per day. The main reasons offered for HP use were "organizational policy" and the "need to look after hearing" health, with the preference being for ear muffs over ear plugs even though policy indicates that the simultaneous use of both is preferable. Because PPE is provided by the organization, the staff is obliged to use the PPE provided by the employer. With reference to the HPs under trial, 13 of the 15 participants found the new devices better than their current HPs.
Trial HP questions
As mentioned previously, the questions concerning the HPs under test were presented framed in a mixture of positive and negative manner for variety and, partially, to act as a reliability check. The responses to the questions are presented separately for the positively and negatively framed questions.
Positively framed questions
The positively framed questions are given in [Table 1].
|Table 1: Positively framed questions with respective mean, standard deviation, mode and frequency of mode |
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Negatively framed questions
The negatively framed questions are given in [Table 2].
|Table 2: Negatively framed questions with respective mean, standard deviation, mode and frequency of mode |
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| Discussion|| |
Graphical representations of the trial HP question results are presented in [Figure 1] as box-and-whisker plots of the mean and 95% confidence interval (CI) for each question. The majority of responses are definitive except for the two questions: "(d) It is a hassle to carry/wear them" and "(e) I am less stressed at work when I wear them".
|Figure 1: Graphical representation of trial HP questions showing mean and 95% confidence interval|
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The category labels, although indicative, should be read in relation to [Table 1] and [Table 2] above.
The general feeling of the respondents was that the trial HPs were an improvement on the performance of the current passive plugs and/or muffs they were using. These protectors allow users to hear sounds and face-to-face conversation that they need to hear; do not interfere with work or current work practices (very important with respect to safety on a firing range); are comfortable to wear for the normal time period required which is between 1.5 and 3.5 hours/day; eliminate unwanted noise while maintaining wanted sounds; are easy to adjust; fit and use; are not stressful to wear; and do not increase feelings of isolation.
The only two points that are not quite as positive overall are that they can be a "hassle to carry/wear all day" and may not be "comfortable to wear all day" . These are the commonly quoted problems by many HP users. ,,
The main limitation of this study is the relatively small sample size of 15 individuals. However, this sample represented the majority of the users at that particular work site. It should also be noted that this was not a typical, industrial work area with miscellaneous background noise and periodic loud machines, plant or power tools in operation. Specifically, it is a firing range where there is relatively little background noise and periodic loud, multiple impulse noise from weapons, ranging up to an L Cpeak of 160 dB. During the quiet periods, instruction is given to students or individuals re-accrediting their operational shooting status. Thus, it is important to be able to continuously wear HPs and avoid the need to constantly remove them while providing instruction and replace them before firing recommences. The constant need to remove and replace HPs has been cited as one of the reasons why HPs are occasionally not replaced.
Positive comments indicated that the use of these devices "allows for better communication with students when on the range and increases safety due to this" (sic). With devices that facilitated Bluetooth® connection, and hence communication between users, one comment stated, "I used … and found the[y] work great especially when communicating with other instructors" and "about time we started looking at these, need to adopt them for safety" . In general, the ability to communicate face-to-face directly by voice was regarded as a definite positive and the Bluetooth® capability provided an extra bonus for most, although there was one response of "no need for Bluetooth®" as there was now less excuse for not hearing phone calls. One comment indicated a possible forward path by suggesting a "separate communications channel to allow for communication with either students OR instructors".
The work area where these devices were trialled is staffed by instructors and trainers with many years and experience on active duty and in training situations. They are the sort of individuals who represent a significant resource of the organization and cannot be easily replaced. Their loss from duty and ability to be deployed can cause difficulty in the operational capacity of the organization. Supplying the HPs that have increased performance to allow valuable individuals to perform at the highest level while maintaining protection of hearing more than offsets any relatively small increase in the cost of providing more sophisticated PPE . The increased cost of supplying electronic, sound restoration, level-dependent ear muffs compared to traditional passive HPs is frequently, anecdotally, cited as a reason for retaining the use of passive HPs in the workplace. Compared to the effort and cost of replacing experienced staff who may be obliged to be relocated due to a hearing loss acquired due to workplace noise exposure, the increased cost is minimal.
| Conclusion|| |
The results of this workplace trial of electronic, sound restoration level-dependent HPs are overwhelmingly favorable from the trainers and instructors. The ability to communicate both face-to-face and/or use an electronic communications link meant that HPs could essentially remain in place over the whole duration while on the firing ranges, thus increasing the wear time and reducing the change on noise injury from unexpected weapon discharges. The use of these devices in such workplaces would seem to be an improvement of current practices where passive devices are normally worn.
| Acknowledgments|| |
The author would like to thank personnel at the New South Wales Police Force Weapons and Tactics Unit, Wetherill Park, for their willingness to participate in the trial with no direct benefit, inducement, or remuneration, other than offering their experience and advice. In particular, Sergeant Warren Brown, Team Leader (Research), Operational Skills Command, is thanked for his advice and assistance in arranging the trial. Thanks also to Megan Gilliver at NAL for assistance in arranging the questionnaire used for this study.
| References|| |
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|5.||Casali JG, Robinson GS. "Augmented" HPDs: Active Noise Reduction, Level-Dependent, Sound Transmission, Uniform Attenuation, and Adjustable Devices - Technology Overview and Performance Testing Issues. In: Suter A, editor. United States Environmental Protection Agency, Workshop on Hearing Protector Devices, Papers and Proceedings. Washington DC, Mar 2003. p. 62-111. |
|6.||Ong M, Choo JT, Low E. A self-controlled trial to evaluate the use of active hearing defenders in the engine rooms of operational naval vessels. Singapore Med J 2004;45:75-8. |
|7.||Williams W, Purdy SC. The reliability of self-reported hearing difficulties from occupational noise exposure. J Occup Health 2008;24:143-53. |
|8.||Purdy S, Williams W. Development of the Noise at Work Questionnaire to assess perceptions of noise in the workplace. Int J Occup Health Saf 2002;18:77-83. |
|9.||Broughton KA. Comfort aspects of ear protection - a Review, Physical Agents Group, Technology and Health Science Division, Health and Safety Executive, UK, 1995. |
|10.||Williams W. Is it reasonable to expect individuals to wear hearing protectors for extended periods? Int J Occup Saf Ergon 2009;15:175-81. |
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National Acoustic Laboratories, Chatswood, NSW
Source of Support: None, Conflict of Interest: None
[Table 1], [Table 2]
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