A study on the correlation between annual noise exposure (ANE) and auditory attention,as well as hearing loss in military personnel

Abstract

BACKGROUND:

The accurate processing of auditory signals holds significant importance in military occupations and can be adversely affected by exposure to noise.

OBJECTIVES:

This study investigates the correlation between annual noise exposure (ANE) and military personnel’s auditory attention and hearing loss.

METHODS:

This study assessed 220 military personnel serving in an armored brigade unit. The Noise Exposure Questionnaire (NEQ) was employed to quantify annual noise exposure, while the Dichotic Digits Test (DDT) was used to measure auditory attention. Additionally, the study examined the hearing threshold of personnel across frequencies ranging from 500 to 8000 Hz.

RESULTS:

The mean ANE among the personnel was 76.80±7.26 dB, and the average number of correct responses in the Dichotic Digits Test (DDT) was 73.74±4.85. The results of the correlation analysis indicated a significant inverse relationship between annual noise exposure and auditory attention (P < 0.001), as well as a notable direct correlation between personnel’s annual noise exposure and hearing loss across all frequencies (P < 0.001).

CONCLUSIONS:

The results of this study showed that the increase in annual noise exposure has increased the rate of hearing loss in both ears and decreased the auditory attention of military personnel.

Keywords

Noise hearing loss attention military personnel

1 Introduction

Noise, an unpleasant and undesirable phenomenon, can trigger a range of adverse effects, including hearing impairment, sleep disturbances, hypertension, coronary artery diseases (CAD), and gastrointestinal ulcers. Initial exposure to noise may lead to temporary hearing loss, but repeated exposure to high-intensity noise eventually results in permanent hearing loss, rendering recovery impossible due to severe damage to the auditory system [1 –3].

Hearing impairment stemming from noise is particularly prevalent in military vocations, where the use of hearing protection devices is often impractical to ensure the audibility of warning signals and instructions. Consequently, noise-induced hearing loss is a prevalent injury among American military retirees [4]. All military personnel are routinely subjected to high-intensity noise levels far exceeding those encountered in most civilian occupations. For instance, military weaponry can generate sounds exceeding 140 dB [5]. Prolonged exposure to continuous noise can induce hearing impairment over time, whereas a single instance of uncontrolled exposure to a thunderous impulse noise event can cause irreversible damage to the auditory system [6]. The continuous exposure to impulse noise from gunfire and explosions is a defining characteristic of military roles [7].

As a deleterious environmental factor, noise can impair hearing and negatively impact individuals’ cognitive performance. Numerous studies have explored the connection between noise and cognitive functioning. Research findings indicate that noise can compromise cognitive performance by impairing information processing [8 –10]. Auditory attention, a critical cognitive indicator, involves the selective comprehension of specific auditory messages while comparatively disregarding information received from other sensory modalities [11, 12]. In military roles, auditory attention holds particular significance, as damage to auditory information processing and hearing loss can significantly impede a military personnel’s ability to receive critical audio signals and communication cues from fellow operatives and external sources. This can lead to human errors and mistakes in executing strategic responses, misinterpreting audio signals, and irreparable accidents and consequences [13, 14]. Consequently, auditory recognition (encompassing hearing acuity and auditory attention) constitutes an essential requirement in tactical training due to the inherent noise exposure during training and missions.

Quantifying noise exposure poses challenges due to the diverse nature of exposure types (continuous and impulse noise) and the absence of a consistent exposure pattern, as observed in industrial settings. Moreover, military personnel encounter various noise sources in their residential and non-occupational environments, exacerbating the effects of noise in addition to occupational exposure [15, 16]. The NEQ, developed by Johnson et al., can be employed in this context to address this. This questionnaire assesses both occupational and non-occupational noise exposure (continuous and impulse), providing a quantitative measure of mean annual noise exposure in decibels for military personnel [17].

Occupational exposure to noise in military personnel is high due to working with weapons and military facilities. Non-occupational exposure to noise is also possible for these personnel. In addition, long-term measurement of these exposures objectively is not possible due to the uncertain spatial and temporal pattern of work. Also, in military jobs, the correct performance of auditory responses is very important. It can be affected by noise. Therefore, the aim of this study in the first step was to investigate the situation of annual exposure to noise in military personnel using the NEQ questionnaire. In the next step, the relationship between annual noise exposure and hearing loss and auditory attention has been investigated.

Given the heightened significance of noise exposure within military organizations due to their interactions with military weaponry and infrastructure, along with the critical nature of auditory responses in such roles, which can be compromised by noise exposure, this study aims to explore the relationship between annual noise exposure and auditory attention, as well as hearing loss, among military personnel.

2 Method

2.1 Research sample

The permission to enter the studied military barracks was obtained after receiving the code of ethics IR.BMSU.REC.1400.107. The participation of people in this study was done fully knowingly and with consent. Sufficient explanations about how to complete the questionnaire individually and the main purpose of the study were provided to the participants. All information collected has been strictly confidential. A total of 220 military personnel from an armored brigade unit of the Army Ground Forces participated in this study using specific inclusion and exclusion criteria. The inclusion criteria of this study included work experience of at least 1 year and age of at least 20 years (in the range of 20–50 years). Participants had to exhibit desirable general health, with a score of less than 23 on the General Health Questionnaire (GHQ-28), and good cognitive performance, as indicated by a score of less than 25 on the Cognitive Failures Questionnaire (CFQ). Exclusion criteria encompassed individuals with any otolaryngology diseases, severe head trauma, neurological disorders, exposure to ototoxic chemicals, medication usage, substance abuse, or smoking. It should be mentioned that the criteria for entering and exiting the study were examined through self-reporting of people, standard questionnaires, and complete hearing system examinations (tympanometry and otoscopy) by an audiologist using clinical equipment. According to the exclusion criteria, 12 participants were excluded from the study.

2.2 Noise exposure questionnaire (NEQ)

The current study employed the “Noise Exposure Questionnaire (NEQ): A Tool for Quantifying Annual Noise Exposure,” designed by Johnson et al. [17]. This questionnaire has been rigorously evaluated and confirmed for validity and reliability, making it a reliable instrument for estimating annual noise exposure (ANE).

The NEQ prompts participants to recollect their involvement in specific noisy activities and occupational noise exposure over the past year. The questionnaire comprises 11 sections, each requiring participants to provide information regarding the frequency and duration of noise exposure and their use of hearing protection devices. Participants in each department are expected to report their exposure rates to different sound sources over the preceding year as follows:

The first section (questions 1 to 3) pertains to the use of electrical tools.

The second section (questions 4 to 6) focuses on using heavy and noisy equipment and machinery.

The third section (questions 7 to 9) covers participation in sports events and entertainment involving music, such as concerts.

The fourth section (questions 10 to 12) addresses the use of motor vehicles.

The fifth section (questions 13 to 15) deals with exposure to aircraft noise.

The sixth section (questions 16 to 18) pertains to the use of firearms.

The seventh section (questions 19 to 21) relates to playing musical instruments.

The eighth section (questions 22 to 23) involves listening to music and media programs via hands-free and headset devices.

The ninth section (questions 24 to 25) encompasses listening to music and media programs through speakers at home or in vehicles.

The 10th and 11th sections (questions 26 to 31) specifically focus on exposure to occupational noise during summer and other seasons.

The doses of ad hoc (occasional) and occupational noise exposures are calculated separately using the following equation (Eq. 1):

D = \frac{C}{T} \times 100

(1)

In this equation, C represents the hours of noise exposure, determined by multiplying the frequency of exposures by the duration of exposure for each activity, following the prescribed method (Eq. 2).

\begin{matrix} C = Score for frequency of exposures \times \\ Score for duration of exposure \end{matrix}

(2)

Score for the frequency of exposures:

Daily = 200, weekly = 50, monthly = 12, some months = 1.

Score for the duration of exposure:

Over 8 hours = 8; 4–8 hours = 6; 1–4 hours = 3; less than an hour = 1.

The calculation of T is based on the following equation (Eq. 3):

T = \frac{8760}{2 \frac{L - 79}{3}}

(3)

Where: L: The estimated noise exposure (in dB) in each activity based on previous studies within the weighted network A.

The dose equation (D = C/T×100) is also employed to determine the rate of noise exposure for daily routine activities. In this case, the value of C is derived from the difference between the total hours obtained from ad hoc and occupational exposures and 8760 hours. The number 8760 signifies the total hours of noise exposure throughout the year (365×24). The value of L is set at 64 dB, representing the typical sound level for quiet daily activities, as established by the study conducted by Neitzel et al. for T calculation.

Subsequently, the individual doses calculated for each question (each activity) are summed, yielding the annual noise exposure, LAeq8760 h, as per the following equation (Eq. 4):

LAeq 8760 = [10 \times log (\frac{D}{100})] + 79

(4)

L denotes the noise exposure level (in dB on the A-weighted scale), and the rate of change equals 3 dB (NIOSH standard). In this equation, 8760 refers to the total hours of noise exposure, both occupational and non-occupational, over a year. According to recommendations from NIOSH (the National Institute for Occupational Safety and Health), individuals with an annual noise exposure exceeding 78.6 dB (LAeq8760≥79) are considered at high risk of hearing loss due to noise exposure. Using the recommended 3-dB exchange rate, we extrapolated the NIOSH REL of 85 LAeq2000 h to an annual equivalent exposure limit of 78.6 LAeq8760 h. For purposes of our study, participants with LAeq8760 h values of ≥79 were considered to be at high risk for developing NIHL [18].

It is important to note that the use of firearms is not factored into the calculation of D in the dose measurements, as this type of exposure falls under impulse exposure and differs from continuous noise exposure.

The quantitative face validity results indicated that all questions received impact scores exceeding the standard threshold; therefore, the questionnaire retained all questions. Furthermore, the results of the content validity index (CVI) and content validity ratio (CVR) exceeded 0.79 and 0.56, respectively. The internal consistency and reproducibility of this questionnaire were corroborated through Cronbach’s alpha coefficient (0.81) and test-retest analysis (P-value <0.001, r = 0.922). Consequently, the present questionnaire has been validated and established as valid and reliable.

2.3 Dichotic digits test (DDT)

Numerous tests, including the DDT, have been devised to assess auditory attention. This particular examination evaluates dichotic integration skills. Its notable advantages encompass user-friendliness, swift administration (requiring less than five minutes), the facility for expeditious score computation, ease of responding, and straightforward comprehension of the test directives [11 , 20].

This test was conducted in an office room with equipment such as laptops, headphones, and DDT test tools in the studied armored unit that was assigned for this purpose. The test items consist of monosyllabic numerals from one to ten except number 4 in Persian. In each stage, two numbers are played in the right ear and two numbers in the left ear simultaneously. The participants received a total of 80 numbers in both ears, 40 numbers in each ear during the test. The desired numbers have been played in the ears of the participants using the mentioned equipment with a sound level of 50 dB through headphones. Subsequently, the examinee’s responses are meticulously documented on the scoring sheet, with a positive point attributed to each correct response. Ultimately, the tally of accurate answers yields the final score for this test, with a maximum achievable score of 80 [21]. It should be mentioned that the researchers of this study gave the necessary training to the participants on how to perform the test correctly before starting the test and had sufficient supervision during thetest.

2.4 Assessment of hearing loss

The latest audiometric test information available in the personnel’s job file, which was conducted during the past year, was used to check the hearing loss of the personnel. These tests are based on ISO 8253-1 : 2010 standard and after hearing rest. In this study, the recorded values of air conduction audiometry at frequencies of 500, 1000, 2000, 3000, 4000, 6000, and 8000 Hz have been extracted for both ears. Finally, the level of hearing loss of the personnel has been investigated based on the following classification:

Normal: –10 to 15 dB

Slight: 16 to 25 dB

Mild: 26 to 40 dB

Moderate: 41 to 55 dB

Moderately severe: 56 to 70 dB

Severe: 71 to 90 dB

Profound: More than 90 dB

2.5 Statistical analysis

The scores derived from the NEQ were initially tabulated using Excel software, yielding quantitative data for statistical analysis. In conjunction with the information acquired from the DDT and the hearing threshold values across different frequencies, these datasets were entered into SPSS 22 for statistical scrutiny. Within this software, various descriptive methods were employed for data characterization. Subsequently, given the non-normal data distribution, as indicated by a P-value of less than 0.05 for all variables (P < 0.001) in the Kolmogorov-Smirnov test, Spearman’s correlation test was employed to explore associations between variables.

3 Results

In this study, the personnel exhibited a mean age of 37.30±7.87 and an average work experience of 16.98±8.38 years. Additionally, 17 (7.7%) participants were single, while 203 (92.3%) were married. Among the participants, 41 (18.6%) possessed academic qualifications (bachelor’s degrees and higher), while the remainder were undergraduates.

Table 1 presents the incidence of noise exposure resulting from the workers’ ad hoc (occasional) activities.

Table 1
Incidence of Workers’ Occasional Noise Exposure

Episodic activities Number (Percentage)

Exposure frequency Exposure time

Never Every few months Monthly Weekly Daily <1hr 1-4 hr 4-8 hr ≥8hr

Power tools: 106 (48.2) 63 (28.6) 16 (7.3) 20 (9.1) 15 (6.8) 158 (71.8) 49 (22.3) 13 (5.9) 0 (0)

Equipment/machinery: 124 (56.4) 58 (26.4) 10 (4.5) 28 (6.4) 0 (0) 163 (74.1) 45 (20.5) 12 (2.7) 0 (0)

Sporting/entertainment: 152 (69.4) 43 (19.6) 16 (7.3) 8 (3.7) 0 (0) 177 (80.5) 28 (12.7) 15 (6.8) 0 (0)

Motorized vehicles: 47 (21.4) 49 (22.3) 28 (12.7) 48 (21.8) 48 (21.8) 114 (51.8) 90 (40.9) 16 (7.3) 0 (0)

Aircraft: 155 (70.5) 58 (26.4) 7 (3.2) 0 (0) 0 (0) 171 (77.7) 49 (22.3) 0 (0) 0 (0)

Musical instrument: 188 (85.5) 17 (7.7) 5 (2.3) 8 (3.6) 2 (0.9) 202 (91.8) 10 (4.5) 8 (3.6) 0 (0)

Music listening (headsets or earphones): 87 (39.5) 61 (27.7) 24 (10.9) 36 (16.4) 12 (5.5) 178 (80.9) 31 (14.1) 11 (5) 0 (0)

Music listening (speakers): 50 (22.7) 32 (14.5) 31 (14.1) 66 (30) 41 (18.6) 142 (64.5) 57 (25.9) 21 (9.5) 0 (0)

Episodic activities	Number (Percentage)
Power tools:	106 (48.2)	63 (28.6)	16 (7.3)	20 (9.1)	15 (6.8)	158 (71.8)	49 (22.3)	13 (5.9)
Equipment/machinery:	124 (56.4)	58 (26.4)	10 (4.5)	28 (6.4)	0 (0)	163 (74.1)	45 (20.5)	12 (2.7)
Sporting/entertainment:	152 (69.4)	43 (19.6)	16 (7.3)	8 (3.7)	0 (0)	177 (80.5)	28 (12.7)	15 (6.8)
Motorized vehicles:	47 (21.4)	49 (22.3)	28 (12.7)	48 (21.8)	48 (21.8)	114 (51.8)	90 (40.9)	16 (7.3)
Aircraft:	155 (70.5)	58 (26.4)	7 (3.2)	0 (0)	0 (0)	171 (77.7)	49 (22.3)	0 (0)
Musical instrument:	188 (85.5)	17 (7.7)	5 (2.3)	8 (3.6)	2 (0.9)	202 (91.8)	10 (4.5)	8 (3.6)
Music listening (headsets or earphones):	87 (39.5)	61 (27.7)	24 (10.9)	36 (16.4)	12 (5.5)	178 (80.9)	31 (14.1)	11 (5)
Music listening (speakers):	50 (22.7)	32 (14.5)	31 (14.1)	66 (30)	41 (18.6)	142 (64.5)	57 (25.9)	21 (9.5)

The table shows that the most frequent ad hoc noise exposure was associated with using motor vehicles and listening to music through speakers. Furthermore, employees’ average occupational noise exposure was 4.83±2 hours per week.

Table 2 displays the outcomes of measurements of annual noise exposure (ANE) and the auditory attention status of the workers.

Table 2

Annual Noise Exposure and Auditory Attention Status in Workers

	Mean	Standard Deviation	Minimum	Maximum
ANE (LAeq8760)	76.80	7.26	64.40	89.45
DDT	73.74	4.85	48.00	80.00

According to Table 2, the mean annual noise exposure of the workers remained below the permissible limit of ANE (LAeq8760 = 79). Similarly, Table 3 elucidates the status of individuals’ continuous and impulse noise exposure.

Table 3

Workers’ Continuous and Impulse Noise Exposure

	Number	Percentage
LAeq8760 < 79	120	54.5
79 LAeq8760≥	100	45.5
Firearm exposure	220	100

As indicated in the table, 100 of the personnel (45.5%) had risk criteria for NIHL (≥79 LAeq8760 h). All personnel had experienced exposure to firearms such as rifles, pistols, tanks, and cannons. Remarkably, none of the personnel consistently employed hearing protection equipment when exposed to occupational noise.

The results of the hearing loss of the participants in this study indicated that 44 personnel (20%) had slight hearing loss, 84 personnel (38.2%) had mild hearing loss, 35 personnel (15.9%) had moderate hearing loss, 18 personnel (8.2%) had moderately severe hearing loss, and the rest of the personnel have normal hearing.

Figure 1 showcases the mean hearing threshold results in decibels at various frequencies for both the right and left ears.

Fig. 1

Hearing loss in personnel.

As illustrated in Figure 1, military personnel exhibited hearing loss in both ears due to annual noise exposure. The most substantial hearing loss occurred in both ears at 4000 and 6000 Hz. Across all frequencies, the mean hearing threshold exceeded 10 dB. Furthermore, at frequencies of 4000 and 6000 Hz, the hearing threshold of all workers was at least 10 dB.

Tables 4 and 5 present the correlation matrices between annual noise exposure (ANE) and hearing thresholds in personnel for both the right and left ears, respectively.

Table 4

Correlation Test Results for ANE Scores and Hearing Thresholds (Right Ear)

		Right ear hearing threshold at different frequencies
		500	1000	2000	3000	4000	6000	8000
ANE	Spearman’s Correlation	0.446	0.414	0.433	0.451	0.611	0.531	0.465
	P-value	<0.001	<0.001	<0.001	<0.001	<0.001	<0.001	<0.001

Table 5

Correlation Test Results for ANE Scores and Hearing Thresholds (Left Ear)

		Left ear hearing threshold at different frequencies
		500	1000	2000	3000	4000	6000	8000
ANE	Spearman’s Correlation	0.432	0.415	0.424	0.443	0.554	0.570	0.463
	P-value	<0.001	<0.001	<0.001	<0.001	<0.001	<0.001	<0.001

Based on the findings in Tables 4 and 5, a statistically significant direct relationship is observed between the two variables at the 0.05% significance level. Furthermore, a significant direct correlation is observed between the Annual Noise Exposure (ANE) score and the hearing threshold scores acquired from personnel across various frequencies in both ears. Specifically, an escalation in the ANE scores leads to an exacerbation of hearing loss across all frequencies.

Spearman’s correlation test, conducted at a 0.05% significance level, indicates a significant inverse relationship between the ANE score and the scores obtained from the Auditory Attention test (P < 0.001, r = –0.507). Consequently, an increase in the annual noise exposure rate substantially diminishes the auditory attention abilities of the personnel. Also, examining the results of the correlation coefficient between DDT and the age of the participants was inverse and significant (P < 0.001, r = –0.373), but no significant correlation between DDT and education level was observed.

4 Discussion

The study’s results establish a direct and statistically significant connection between the intensity of annual noise exposure and hearing loss. Furthermore, an elevation in annual noise exposure, whether from occupational or non-occupational sources, substantially elevates the incidence of hearing loss among personnel. This aligns with the findings of Heupa et al., who reported that military personnel exposed to noise, particularly gunfire, suffered damage to their auditory systems and experienced a decrease in their hearing thresholds [22]. Collee et al. investigated noise exposure and the prevalence of hearing loss among Belgian military personnel, revealing that infantry and commando forces were particularly susceptible to hearing loss due to exposure to loud noises, such as gunfire from large-caliber weapons [23]. Al-Omari et al.’s study, examined the association between noise-induced hearing loss, flight time, and aircraft type. Their research revealed an 18% prevalence of hearing loss among military pilots, with fixed-wing aircraft pilots more affected than rotary-wing aircraft pilots [24]. Rezaei et al.’s investigation into impulse noise and acoustic trauma among military personnel following shooting incidents corroborates the potential for sound trauma even with exposure to such noises, emphasizing the necessity of hearing protection equipment and effective monitoring programs for these occupations [25]. These findings underscore the importance of prioritizing measuring and preserving hearing health in military personnel.

Some researchers have broadened their focus to include non-occupational exposures alongside occupational ones, as exemplified by Neitzel et al. and Beach et al. Neitzel et al. delved into non-occupational factors influencing noise exposure among construction workers. Participants in their study completed questionnaires regarding non-occupational activities, with non-occupational noise exposure levels estimated in decibels based on prior research. Notably, over 9% of non-occupational exposures, such as attending concerts, working with noisy equipment, and shooting, exceeded permissible limits (85 dB) [26]. Beach et al. examined noise exposure during leisure activities, hearing loss, and related symptoms, concluding that individuals participating in noisy leisure activities, such as attending concerts and listening to loud music, experienced hearing damage symptoms at an earlier stage [16]. An investigation of hearing loss among military personnel concerning work-related and leisure-time activities revealed that approximately 67% of personnel had mild hearing loss, while roughly 9% suffered from severe hearing loss. It is important to note that noisy, non-occupational activities can influence work-related hearing loss but cannot solely cause it [15]. These outcomes align with the present study, emphasizing the significance of non-occupational activities as factors influencing noise exposure levels and hearing loss among personnel.

The findings of this study reveal an inverse and significant relationship between NEQ scores and the results of the DDT. Consistent with the outcomes of the current investigation, several prior studies have explored the adverse impact of noise on cognitive functions, particularly attention control. For instance, Kumar et al. reported that individuals with standard audiometry experienced a decline in auditory processing skills when exposed to noise levels exceeding 80 dB compared to those not exposed to such noise [9]. Mehrkian et al. found that noise exposure had irreversible effects on memory and central auditory processing, and in addition to hearing loss, it could result in speech recognition and comprehension disorders among workers [27]. Furthermore, Zeidabadi et al. observed that occupational noise levels exceeding the exposure limit of 85 dBA impacted various aspects of cognitive functioning, including attention [28].

According to these studies, noise, in the form of tinnitus, can hinder hearing and attention, with individuals suffering from tinnitus experiencing more concentration and attention problems than those without these symptoms [29]. However, some earlier studies did not identify any significant relationship between noise exposure and attention, and it was even reported that sound could temporarily increase individuals’ levels of alertness by stimulating excitement upon initial exposure, which subsequently reduced its negative consequences [30 –32]. For example, Stansfeld et al. noted that the noise generated by road traffic and airplanes did not affect individuals’ sustained attention [30]. This result contradicted the findings of the present study. The discrepancy can be attributed to differences in study populations, participants’ age ranges, noise exposure levels, the nature of the noise, duration of noise exposure, and variations in the assessment tools used. Notably, no prior research has directly investigated the effect of annual noise exposure on auditory attention in military personnel, making this study’s findings particularly valuable in this area.

Given that sound pressure level plays a crucial role in auditory attention and loss, this study indicates that an increase in annual noise exposure leads to a loss of hearing thresholds at all frequencies in both ears and a reduction in participants’ auditory attention. Exploring the potential reasons behind this result, prolonged exposure to elevated noise levels can damage the cochlea and reduce hearing sensitivity by impairing the synaptic connections between the inner hair cells of the cochlea and auditory nerve fibers. Furthermore, auditory processing necessitates hearing as a sensory process and its interpretation as a perceptual-cognitive process. Therefore, the interaction between these two processes is essential for auditory recognition. Noise exposure can disrupt and alter this auditory information’s processing and accurate interpretation [2 , 34]. These factors may explain the results of the present study, wherein increased annual noise exposure led to more significant disruption in the perception and processing of auditory signals among personnel, resulting in increased deterioration of hearing thresholds and reduced auditory attention.

4.1 Limitations

From the strengths of this study, it can be said that for the first time, a questionnaire tool has been used to measure the sound level in military personnel, and its relationship with auditory attention in military personnel has been discussed. One of the limitations of this study can be mentioned that it was conducted in one occupational field (military personnel) and one country, so that the generalization of these results to other countries and other occupational groups requires more research. Other limitations of the study include the lack of categorization of occupational groups for a more detailed examination of the results (due to criteria established by the armored unit) and the unavailability of objective noise measurement data. Therefore, the authors recommend that in future studies, more advanced methodologies such as prospective designs and objective studies should be used to investigate the effect of other interventions in causing hearing loss and auditory attention.

5 Conclusion

In light of the findings of this study, it becomes evident that exposure to loud noises can heighten the risk of hearing loss and diminish auditory attention in military personnel. Given that military personnel frequently encounter uncontrollable impulse noise generated by military equipment, such exposure can lead to temporary and irreversible damage to their auditory systems. Furthermore, non-occupational, occasional, or daily noise exposures can occur in individuals, and in conjunction with occupational exposures, they can exacerbate the auditory effects of noise.

Moreover, assessing occupational and non-occupational noise exposure over extended periods is expensive, time-consuming, and often impractical. This measurement challenge is particularly prevalent in military work settings, characterized by unpredictable spatial and temporal work patterns. Consequently, the NEQ questionnaire can be a valuable tool for assessing annual noise exposure among individuals in various occupations. The questionnaire considers occupational and non-occupational noise exposure history (regular and ad hoc) and separately evaluates exposure to impulse and continuous noise.

Ethical approval

This study was approved by the Ethics Committee of Baqiyatallah University of Medical Sciences (Ethic Code: IR.BMSU.REC.1400.107).

Informed consent

The data has been collected anonymously.

Conflict of interest

The authors declare that they have no conflict of interest.

Funding

This study has been supported by Baqiyatallah University of Medical Sciences. The funding body has played no role in the design of the study, collection of data, analysis of data and interpreting results or in writing the manuscript or in decision to submit the manuscript for publication.

Footnotes

Acknowledgments

The authors extend their heartfelt appreciation to the officials of the armored unit for their wholehearted cooperation in executing this project.

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Episodic activities	Number (Percentage)
	Exposure frequency					Exposure time
	Never	Every few months	Monthly	Weekly	Daily	<1hr	1-4 hr	4-8 hr	≥8hr
Power tools:	106 (48.2)	63 (28.6)	16 (7.3)	20 (9.1)	15 (6.8)	158 (71.8)	49 (22.3)	13 (5.9)	0 (0)
Equipment/machinery:	124 (56.4)	58 (26.4)	10 (4.5)	28 (6.4)	0 (0)	163 (74.1)	45 (20.5)	12 (2.7)	0 (0)
Sporting/entertainment:	152 (69.4)	43 (19.6)	16 (7.3)	8 (3.7)	0 (0)	177 (80.5)	28 (12.7)	15 (6.8)	0 (0)
Motorized vehicles:	47 (21.4)	49 (22.3)	28 (12.7)	48 (21.8)	48 (21.8)	114 (51.8)	90 (40.9)	16 (7.3)	0 (0)
Aircraft:	155 (70.5)	58 (26.4)	7 (3.2)	0 (0)	0 (0)	171 (77.7)	49 (22.3)	0 (0)	0 (0)
Musical instrument:	188 (85.5)	17 (7.7)	5 (2.3)	8 (3.6)	2 (0.9)	202 (91.8)	10 (4.5)	8 (3.6)	0 (0)
Music listening (headsets or earphones):	87 (39.5)	61 (27.7)	24 (10.9)	36 (16.4)	12 (5.5)	178 (80.9)	31 (14.1)	11 (5)	0 (0)
Music listening (speakers):	50 (22.7)	32 (14.5)	31 (14.1)	66 (30)	41 (18.6)	142 (64.5)	57 (25.9)	21 (9.5)	0 (0)