The Effect of Using an Active Earmuff on High Frequency Hearing in United States Marine Corps Weapons Instructors
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Annals of Work Exposures and Health, 2021, 1–9
https://doi.org/10.1093/annweh/wxab067
Original Article
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Original Article
The Effect of Using an Active Earmuff on High
Frequency Hearing in United States Marine Corps
Weapons Instructors
Jeremy Federman1,*, Stephanie Karch1, Christon Duhon2, Linda Hughes1
and Devon Kulinski1,3
1
Submarine Medicine and Survival Systems, Naval Submarine Medical Research Laboratory, Groton, CT
06349, USA; 2Naval Hospital Beaufort, Audiology Department, MCRD Parris Island Branch Health Clinic,
Parris Island, SC 29902, USA; 3Leidos, Inc., Reston, VA 20190, USA
*Author to whom correspondence should be addressed. Tel: +1-860-694-5798; e-mail: Jeremy.S.Federman.Civ@mail.mil
Submitted 24 February 2021; revised 21 June 2021; editorial decision 21 June 2021; revised version accepted 17 August 2021.
Abstract
Objectives: To investigate the change in hearing and perceived comfort over 1 year related to using
an active hearing protection device (HPD) among United States Marine Corps (USMC) personnel
routinely exposed to hazardous noise.
Methods: USMC Weapons Instructors (n = 127) were issued an active earmuff that met military
standards and was compatible with other protective equipment. These participants completed pre-
and post-hearing tests and comfort surveys. A control cohort (n = 94) was also included to compare
individual changes in high-frequency pure tone average (HF-PTA) over 1 year.
Results: The control group’s HF-PTA was 3 dB worse than the intervention group after only 1 year.
Survey responses revealed perceived improvements in the ability to hear and understand, situ-
ational awareness, and safety.
Conclusions: Active HPDs can reduce hearing loss and improve hearing-related occupational tasks.
Keywords: attenuation; comfort; hearing protection device (HPD); military; Weapons Instructor
Introduction the US Department of Veterans Administration (2019);
with more than 1.2 million diagnosed Veterans reported
The US Navy and Marine Corps Public Health Center
in 2018 alone. The occurrence and characterization of
(2016) reported that as many as 20% of the United States
hearing loss among US military SMs is well documented
Marine Corps (USMC) active duty service members (SMs)
throughout the literature (Barney and Bohnker, 2006;
had a known hearing loss reported for calendar year 2015.
Helfer et al., 2010, 2011; Theodoroff et al., 2015; Wells
Second only to tinnitus, hearing loss is the next most
et al., 2015; Yong and Wang, 2015; Brungart et al., 2019).
common military service-connected disability reported by
Published by Oxford University Press on behalf of The British Occupational Hygiene Society 2021.2 Annals of Work Exposures and Health, 2021, Vol. XX, No. XX
What’s Important About This Paper?
Active hearing protection devices amplify sounds of interest while protecting against potentially damaging
noises, facilitating situational awareness and communication in environments with hazardous noise.
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Weapon Instructors in the U.S. Marine Corps assigned to use of an active hearing protection device ex-
perienced less decline in high frequency hearing sensitivity after 1 year, relative to the control group; and
reported the device to improve communication and safety during active shooting. Active hearing protection
devices can help to prevent hearing loss, a ubiquitous, avoidable occupational disability.
In the military environment, the criteria for conducted by the National Institute for Occupational
designating a noise as hazardous (both continuous and Safety and Health’s Health Hazard Evaluation Program
impulse/impact) are well defined by both the Department (Brueck et al., 2014) reported loudness levels of 160 dBP
of Defense (US Department of Defense, 2019) and indi- at the location where an instructor would typically stand
vidual branches of service (US Army, 2015; Commandant during a live-fire training exercise using M4s at an out-
of the Marine Corps, 2016; US Air Force, 2016; US door firing range. A SM would therefore need to achieve
Navy, 2019). Steady-state or continuous noises (e.g. at least 25 dB of attenuation in order to reduce the im-
motor transport vehicles, ship engine rooms, and power pulse noise from a M16 to the permissible noise level
generators) are considered hazardous when they are of 140 dBP or less at the ear. Not only are the issuance
greater than 84 decibel A-weighted (dBA). Conversely, of HPDs common practice to mitigate noise exposure,
impulse or impact noises (e.g. weapon system, weapon prior studies have demonstrated that with training, re-
fire, explosive device) require intervention when they ex- corded attenuations in the field (i.e. outside of a labora-
ceed 140 dB peak (dBP). Unique to the military is the tory setting) can meet or exceed 25 dB with either a
frequency with which SMs find themselves in a complex, single in-ear foam HPD (Federman and Duhon, 2016) or
hazardous noise environment that is comprised of both passive over-the-ear HPD (Liu and Yang, 2018).
multiple high-level impulsive events occurring simultan- HPDs can operate as either a passive or active de-
eously with hazardous steady-state noise. vice (Berger, 2003). Passive style devices provide a phys-
Exposure to hazardous noises that are either con- ical barrier for the airborne acoustic energy and do not
tinuous or impulsive can lead to noise-induced hearing require a battery or power source to operate. Passive
loss (NIHL). Specifically, NIHL is characterized by a devices are either linear or non-linear. Linear HPDs pro-
reduction in hearing sensitivity between 3 and 6 kHz vide the same amount of attenuation, regardless of noise
(Durch et al., 2006). Unprotected exposure [i.e. nonuse, intensity. Because impulsive noise sources have much
under-use, or improper fit of hearing protection devices higher peak intensities than continuous noise sources
(HPDs)] to hazardous noises can result in hearing loss, with equal energy, non-linear, or level-dependent, passive
either temporary or permanent. Temporary hearing loss, devices attenuate continuous and impulse noises differ-
or temporary threshold shift, has been reported to be ently. According to Casali et al. (2009), passive HPDs
the strongest predictor for SMs who experience hearing have been ‘implicated in compromised auditory percep-
difficulties (Brungart et al., 2019). In this report, the tion, degraded signal detection, reduced speech commu-
authors used the term ‘hearing difficulties’ to refer to nication abilities, and diminished situational awareness’
tinnitus, understanding speech in the presence of back- (p. 69). To mitigate these degradations, active HPDs
ground noise, sensitivity to loud sounds, and the dimin- use a power source to amplify sounds that may be of
ished ability to localize sound. interest (e.g. speech and communication) but still protect
The Marine Corps Hearing Conservation Program against potentially damaging noises (e.g. weapon fire).
(Commandant of the Marine Corps, 2016) mandates This provides the user an ability to maintain situational
that all personnel (SMs and civilians) who are exposed to awareness (SA) and communication in hazardous noise
weapon fire use HPDs that will reduce the exposed noise environments. However, an active HPD performs similar
level below 140 dBP. The M16 and M4A1 rifle weapon to a passive HPD when its power is lost, it is turned off,
systems are currently fielded and utilized by the USMC in or when it actively responds to high-level impulse noises
basic marksmanship training. Upon firing, both weapon like that of weapon fire (Buck, 2009).
systems have been reported to emit roughly 165 dBP Military Weapons Instructors (WIs; i.e. Marksm
near the shooter when fired without use of a suppressor anship Instructors, Small Arms Weapons Instructors, and
(US Army Public Health Command, 2013). A study Marksmanship Coaches) require the ability to recognizeAnnals of Work Exposures and Health, 2021, Vol. XX, No. XX3
speech and communicate effectively with recruits, fellow and was determined not to be human subject research.
instructors, and their chain of command during training Rather, it was determined to be a study investigating mili-
evolutions in order to successfully complete their mis- tary hearing conservation program improvement.
sion. Anecdotally, WIs must also maintain constant SA
of their environment and equipment (i.e. monitor for
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Participants
proper function) during live-fire exercises. The ability to A total of 297 USMC Active Duty WIs stationed at
maintain SA and communication are often perceived by Parris Island, SC and Camp Pendleton, CA were included
the WI to be of greater importance than self-protection in this study. The operational definition of a WI used
against hazardous noise levels. As a result, anecdotally, in this study were junior enlisted (E3 to E6) Marines
WIs have been observed to purposely fit HPDs incor- who worked on a weapons range, and whose Military
rectly, exhibited as either partial or incomplete insertion, Operational Specialty (MOS) was one of the following:
in order to improve access to auditory information so Rifleman, Infantry Assaultman, Marksmanship Coach,
that SA, speech recognition, and communication are Marksmanship Instructor, Light Armor Vehicle Marine,
maintained (Abel, 2008). Such strategies create a conflict Reconnaissance Marine, Machine Gunner, Antitank
between unit mission and DoD hearing conservation Missile Gunner, Infantry Unit Leader, Field Artillery
program policy. Cannoneer, Field Artillery FDC, and Ammunition
Nonuse, under-use, and even misuse of HPDs that Technician.
result in hearing conservation program noncompliance A total of 203 WIs comprised the intervention group
are also known to be attributed to comfort (Berger and were issued the alternative active HPD. Participants
et al., 2003; Arezes et al., 2008; Davis, 2008; Byrne completed audiometric testing (pre- and post-HPD issu-
et al., 2011; Smith et al., 2014; Doutres et al., 2019). ance) and surveys (pre- and post-HPD issuance). A total
A review of the literature revealed a diverse plethora of 76 WIs were excluded from data analysis due to in-
of definitions for HPD ‘comfort’. As it relates to HPDs, complete datasets, thus reducing the total for the inter-
Doutres et al. (2019) determined that comfort is deter- vention group to 127, or 254 ears. Incomplete datasets
mined by users in four distinct subjective categories: were due to (i) loss to follow up, (ii) relocation to an-
physical contact between the HPD and body (e.g. other command prior to the conclusion of data col-
weight, pain, pressure), functionality (e.g. usability), lection, and (iii) separation from service prior to the
acoustics (e.g. SA, communication), and psychology conclusion of data collection.
(e.g. acceptability). The use of surveys to measure and A total of 94 WIs (188 ears) comprised a matched
quantify user opinion and attitudes of HPD is well comparison group. The match criteria for the com-
documented throughout the literature (Arezes and parison group were junior enlisted personnel (E3 to E6),
Miguel, 2002; Arezes et al., 2008; Byrne et al., 2011; who: (i) worked on a weapons range, (ii) were assigned
Davis et al., 2011; Williams, 2011; Bockstael et al., a MOS that resulted in routine exposure to hazardous
2012; Samelli et al., 2018). noise such as weapon fire; and (iii) had audiometric data
The aim of this study was to investigate the effect in the Defense Occupational Hearing and Environmental
of issuing an active HPD to a group of USMC Weapon Readiness System Data Repository (DOHERS-DR) be-
Instructors (WIs) for use while on the range in order to tween September 2012 and June 2015. All subjects
reduce the rate of HPD noncompliance (i.e. nonuse or included in the matched comparison group were con-
under-use), and thereby decrease the rates of high fre- firmed to work on a weapons range by safety personnel.
quency hearing loss. The metrics used to investigate user
change in compliance and HPD use were: (i) measur- Materials
able high frequency hearing loss [i.e. difference in high- All participants in the intervention group were issued the
frequency pure tone average (HF-PTA)] over the span same HPD, which was a one-size-fits-all active earmuff
of 1 year; and (ii) perceived HPD comfort (physical, (NRR = 23 dB). The earmuff used was battery powered,
functional, and acoustic). At this time, the authors are had two microphones (one per earcup) and employed
unaware of any published study or results investigating digital compression circuitry to limit loud sounds
similar questions and cohort. reaching the ear of the user. The used electronic level-
dependent earmuff also met military environmental and
ballistic standards and was compatible with the WIs’
Methods issued helmet. Questions contained in the survey that
This study was reviewed by the Naval Submarine address opinions and attitudes toward issued/used HPD
Medical Research Laboratory Institutional Review Board (Within the military community, HPDs are commonly4 Annals of Work Exposures and Health, 2021, Vol. XX, No. XX
and routinely referred to as earpro. The authors opted to factor was completed to determine if the mean change
use the term colloquial term earpro for all survey ques- in hearing differed significantly between ears, between
tions in order to improve recognition and clarity for the HPD groups, or by ear by group interaction. When ap-
participant population.) are shown in Appendix (avail- plicable, post hoc pairwise comparisons were completed.
able at Annals of Work Exposures and Health online). All significance levels were set at P < 0.05. Subject re-
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Only those who were assigned to the intervention group sponses to Likert scale questions were tallied and ana-
completed the survey questions. Statistical analyses were lyzed for group trends over time (0 and 12 months).
completed using commercially available software (IBM
SPSS Statistics, v23, Armonk, NY).
Results
Procedures For the main effect of ear, the mixed design ANOVA test
The intervention group was issued an alternative active did not detect a mean delta HF-PTA difference by ear
HPD for use over the span of 1 year. Upon issuance of (F1, 219 = 0.192, P = 0.66, ηp2 = 0.001), nor was there
the active HPD (0 month), each participant completed an ear by group interaction (F1, 219 = 0.948, P = 0.33,
the study generated questionnaire (Appendix, available at ηp2 = 0.004). A main effect for group was found (F1,
Annals of Work Exposures and Health online) and a pure- 219 = 5.450, P = 0.02, ηp2 = 0.024), the primary factor
tone audiogram. Both the survey and hearing test were re- of interest. Post hoc pairwise comparisons examining
peated approximately 12 months later. Additionally, all the group differences in HF-PTA over the span of
baseline reference audiograms (DD2215) were obtained 1 year (see Fig. 1) showed the comparison group delta
from the DOEHRS-DR upon entry to service. HF-PTA (0–12 months) was 2.99 dB (95% confidence
Comparison group pure-tone audiometric data were interval: 0.47, 5.52) larger than the intervention group’s
obtained from the DOHERS-DR for three distinct time delta HF-PTA.
points: (i) baseline reference audiogram (form DD2215) Descriptive statistics for group HF-PTA for the right
upon entry to service, (ii) annual hearing test (DD2216) ear, left ear, and both (all) ears combined at baseline,
± 3 months to confirmed start date at the weapons range, issuance of active HPD (0 month), and approximately
and (iii) annual hearing test (DD2216) approximately 1 year thereafter (12 months) are reported in Table 1.
12 (±3) months thereafter. A 3-month ‘grace period’ The average number of days between the start (0 month)
was deemed necessary since many matched comparison and conclusion (12 months) of data collection was
group subjects did not have an annual audiogram docu- approximately 11 months, or 350 days (min = 170,
mented within DOHERS-DR. All data were de-identified max = 472).
prior to data analysis. Individual survey responses for HPD comfort (i.e.
The outcome measure of interest was the HF-PTA, a communication, SA, and safety) were tallied, aggregated
monaural mathematical average of auditory threshold (dB) as a group, and analyzed for general trends. Only parti-
obtained at 3, 4, and 6 kHz. Often with continued exposure, cipants in the intervention cohort completed the survey
and over time, the hearing loss ‘noise-notch’ or ‘notch’ can
spread to include adjacent frequencies (Kirchner et al.,
2012). The HF-PTA was calculated prior to any additional
calculations (i.e. HF-PTA delta) or statistical analysis. To de-
termine if a change in high frequency hearing occurred prior
to issuance of the active HPD, the HF-PTA delta for each
ear was calculated between the baseline reference and the
audiogram completed at the time the active HPD was issued
(i.e. baseline HF-PTA minus 0-month HF-PTA). To deter-
mine if a change in high frequency hearing occurred during
the year in which participants used the active HPD was is-
sued, the HF-PTA delta was calculated between 0-month
HF-PTA and 12-month HF-PTA.
Statistical analysis Figure 1. Mean [standard deviation (SD)] difference
(0–12 months) in HF-PTA. For the intervention group (n = 254)
A two-way mixed analysis of variance (ANOVA) test the mean (SD) is −1.8 (7.5) dB, and −4.7 (13.0) dB for the com-
with ear (left, right) as the within-subjects factor and parison group (n = 188). Error bars are ±1 SD. The horizontal
group (intervention, comparison) as the between-subjects gray line indicates a change between audiograms of 0 dB.Annals of Work Exposures and Health, 2021, Vol. XX, No. XX5
Table 1. HF-PTA mean and standard error.
Intervention Comparison
Right ear Left ear All ears Right ear Left ear All ears
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n = 127 n = 127 n = 254 n = 94 n = 94 n = 188
Baseline 6.6 (0.6) 7.2 (0.6) 6.9 (0.4) 6.6 (0.7) 9.2 (1.0) 7.9 (0.6)
0 month 14.2 (1.4) 17.1 (1.6) 15.6 (1.1) 12.7 (1.8) 15.4 (1.8) 14.1 (1.27)
12 months 16.3 (1.5) 18.5 (1.6) 17.4 (1.1) 17.3 (2.2) 20.3 (2.1) 18.8 (1.5)
Baseline to 0-month delta −7.5 (1.4) −9.9 (1.5) −8.7 (1.0) −6.2 (1.6) −6.2 (1.6) −6.2 (1.1)
0- to 12-month delta −2.4 (0.7) −1.4 (0.6) −1.8 (0.5) −4.6 (1.4) −4.9 (1.3) −4.7 (1.0)
Note. Unit of measure for all values in dB.
Figure 2. Intervention group (n = 127) responses to the survey question ‘My CURRENT EARPRO increases how safely I perform
my duties during active shooting’ over the course of 1 year.
(n = 127). The surveys were completed at the time the al- to perform their duties safely had improved with the use
ternative HPD was issued (0 month) and approximately of the issued HPD.
1 year thereafter (12 months). Only questions related to Fig. 3 depicts the percent breakdown of group re-
perception of safety (Fig. 2), audibility (Fig. 3), and SA sponses to the following survey statement: ‘My current
(Fig. 4) revealed observable trends. earpro helps me hear & understand Marines/Recruits
Specifically, Fig. 2 shows the group response to the during weapons firing.’ Prior to issuance of the studied
following statement: ‘My current earpro increases how active earmuff, approximately half (49%) of the WIs sur-
safely I perform my duties during active shooting.’ Prior veyed considered their HPD to negatively affect (strongly
to using the study-issued active earmuff, 54% of re- disagree or disagree) their ability to hear and understand
spondents indicated they were ‘neutral’, i.e. that they other personnel during active shooting on the weapons
viewed their HPD (earpro) neither improved nor im- range. After using the active HPD for approximately
paired their ability to safely carrying out their occupa- 12 months, 87% of the same surveyed group agreed
tional duties during active shooting. After approximately (agree or strongly agree) with this statement.
12 months of using the active earmuff, the total per- Intervention group participants also were asked to rate
centage of respondents who remained neutral dropped their degree of agreement/disagreement with the following
20% points to 34%. Conversely, following intervention, statement: ‘Wearing my current earpro improves my situ-
64% of all surveyed WIs either agreed or strongly agreed ational awareness (e.g., communication with others, detec-
with the statement, indicating they perceived their ability tion of equipment failures, ability to know where sounds are6 Annals of Work Exposures and Health, 2021, Vol. XX, No. XX
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Figure 3. Intervention group (n = 127) responses to the survey question ‘My CURRENT EARPRO helps me hear & understand
Marines/Recruits during weapons firing’ over the course of 1 year.
Figure 4. Intervention group (n = 127) responses to the survey question ‘Wearing my CURRENT EARPRO improves my situ-
ational awareness (e.g., communication with others, detection of equipment failures, ability to know where sounds are coming
from, identification of sounds, etc.).’ over the course of 1 year.
coming from, identification of sounds, etc.).’ As shown in Fig. those who were issued an active HPD (intervention
4, 50% of surveyed WIs rated the HPD (earpro) used prior group) was −8.7 dB, while the mean delta HF-PTA for
to intervention to negatively affect responses. Following inter- those who went without intervention or issuance of an
vention, those who used the active HPD showed an overall alternate active HPD (comparison group) was −6.2 dB.
trend indicating a perceived improvement in SA. A negative HF-PTA points to decreased hearing sensi-
tivity (i.e. increased auditory thresholds) on the subse-
quent hearing test. This finding suggests that although
Discussion a change in high frequency hearing (decreased hearing
Results from this study show that high frequency sensitivity and negative delta HF-PTAs) occurred since
hearing sensitivity (as demonstrated with the HF-PTA) entry to service (DD2215), this change was statistically
decreased from entry to service (baseline) prior to per- similar between groups. Therefore, any further change in
forming duties as a WI. The mean delta HF-PTA for HF-PTA after the start of the study (0-month) time pointAnnals of Work Exposures and Health, 2021, Vol. XX, No. XX7
(i.e. 12-month delta HF-PTA) could be attributed to haz- perform differently to impulse noise than continuous
ardous noise exposure during the study time period and noises (Murphy et al., 2012), they perform differently at
the effectiveness of the type of HPD issued and used by varying intensity levels (Buck, 2009). Strides have been
the WIs. made to document the response of HPDs to multiple
The difference in HF-PTA after 1 year (i.e. 0-month types of sound sources (impulse and continuous) in both
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HF-PTA minus 12-month HF-PTA) for the intervention intensity (i.e. IPIL or NRR) and frequency (impulse spec-
group was −1.8 dB, while the comparison group was tral insertion loss) domains. Fackler et al. (2017) calcu-
−4.7 dB. Statistical analysis of the 1-year HF-PTA delta lated IPIL values for both a single in-ear foam HPD and
revealed a significant difference in HF-PTA between an electronic earmuff when turned off (i.e. passive mode)
the two groups. The post hoc pairwise comparisons, with impulses generated from a shock tube (ANSI/ASA
which examined group differences, revealed the mean 12.42, 2010) and an AR-15. At the highest level tested
change in HF-PTA for the comparison group (n = 188; by the standard (168 dBP), Fackler et al. (2017) reported
X̄dif f = −4.75) was significantly larger than the inter- lower calculated attenuation ratings (IPIL) for the elec-
vention group’s mean HF-PTA (n = 254; X̄dif f = −1.75 tronic earmuff (compared with the foam earplug), and
), thereby supporting the hypothesis that issuing an al- lower levels of attenuation in response to the shock tube
ternative active HPD resulted in less high frequency (compared with the AR-15). This would support that
hearing loss. not only is the protection against impulse noises affected
All WIs in the intervention group were issued the by HPD design but also by the spectral shape, and dur-
same survey at two points in time: (i) when issued the ac- ation of the impulse.
tive HPD, and (ii) approximately 1 year later. The survey Although the work done by Fackler et al. (2017) is
directed the WI to answer the questions with regard to representative of some small-arms weapons, military
their current HPD and their effect on different aspects weapon systems often exceed 168 dBP. The work com-
of comfort (acoustics and functionality). By comparing pleted by Gallagher et al. (2014, 2016) and Murphy
surveys over 1 year of time, we were able to track the et al. (2012) demonstrated that a higher attenuation than
perception of how the HPD was affecting their ability the advertised NRR is achieved in response to an im-
to communicate with Marines/Recruits during weapons pulse noise greater than 166 dBP. And unlike the NRR,
fire, improve individual SA, and perform job duties the amount of attenuation achieved when an HPD is ex-
safely during active shooting. In this context, SA was de- posed to impulse noise, or the IPIL, is not required to be
fined as the ability to communicate with others, to de- tested or to be displayed on the product label making it
tect equipment/weapons failures, to localize sounds in more difficult for consumers, occupational audiologists,
the environment, and to identify sounds. The tallied re- industrial hygienists, and hearing conservationists, to de-
sults indicated a trend that, with use of the active HPD, termine the amount of protection a particular HPD is
the group felt they were able to: (i) hear and understand likely to provide. Future work is needed to expand and
other Marines and Recruits during weapons fire; (ii) ob- define the relationship of high-intensity blasts that are
tain improved SA; and (iii) perform their occupational representative of military weapon systems to which SMs
duties safely during active shooting. This was similarly are exposed.
observed by Williams (2011), who reported that use of
an active HPD was perceived by respondents to facilitate
face-to-face communications and improve the ability to
Conclusion
complete operational duties on the range safely. This study documented a difference in high frequency
The relationship between the actual attenuation hearing between two groups of USMC Weapons
achieved (i.e. PAR value) and the HPD-rated attenuation Instructors. One group (intervention) was issued and
for impulse noise [i.e. impulse peak insertion loss (IPIL)] used an active HPD (NRR 23) on the firing range
is not well understood, thus providing a limitation to for approximately 12 months, while the other group
this work. That is, the amount of attenuation provided (control) did not. Although both group’s 12-month
by the issued active HPD against impulse noises was not high frequency hearing thresholds had worsened (as
measured. The NRR for each HPD is developed using evidenced by negative HF-PTA deltas), a significant
continuous noise, and therefore is a reasonable and difference was found between the two groups. The
well-respected rating for how the HPD works in con- control group was shown to have a greater shift in
tinuous noise environments. However, the NRR is not a high frequency PTA compared with the intervention
valid representation of how the HPD will perform under group. This suggests that the use of the active HPD by
loud impulse noises like weapon fire. Not only do HPDs the intervention group while on duty at the weapons8 Annals of Work Exposures and Health, 2021, Vol. XX, No. XX
range during active shooting positively impacted their prepared by a military service member or employee of the U.S.
hearing health outcomes. The use of survey questions Government as part of that person’s official duties.
revealed that, while using the active HPD, the WIs in
the intervention group generally considered the ac-
Data availability
tive HPD to improve communication, SA and safety
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during active shooting. In a military training or op- The data underlying this article cannot be shared publicly due
erational environment, communication and hearing to government restriction. The data will be shared on reasonable
request to the corresponding author.
requirements specific to a units’ mission should be
taken into consideration. These findings support the
well-accepted recommendation to select the most ap- References
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