Hearing Protection Research Articles

Four-Point Impedance: A Potential Biomarker for Residual Hearing After Cochlear Implantation.

Preservation of residual hearing after cochlear implantation allows for electroacoustic stimulation, which leads to better music appreciation, noise localization, and speech comprehension in noisy environments. Real-time intraoperative electrocochleography (rt-ECochG) monitoring has shown promise in improving residual hearing rates. Four-point impedance (4PI) is being explored as a potential biomarker in cochlear implantation that has been associated with fibrotic tissue response, hearing loss, and dizziness. In this study, we explore whether monitoring both rt-ECochG intraoperatively and postoperative 4PI improves predictions of the preservation of residual hearing. This was a prospective cohort study. Adults with residual acoustic hearing underwent cochlear implantation with intraoperative intracochlear electrocochleography (ECochG) monitoring. The surgeon responded to a drop in ECochG signal amplitude of greater than 30% by a standardized manipulation of the electrode with the aim of restoring the ECochG. At the end of the procedure, the ECochG signal was categorized as being maintained or having dropped more than 30%. 4PI was measured on 1 day, 1 week, and 1 and 3 months after cochlear implantation. Residual hearing was measured by routine pure-tone audiogram at 3 months postoperatively. The ECochG category and 4PI impedance values were entered as factors in a multiple linear regression predicting the protection of residual hearing. Twenty-six patients were recruited. Rt-ECochG significantly predicted residual hearing at 3 months (t test; mean difference, 37.7%; p = 0.002). Inclusion of both 1-day or 3-month 4PI in a multiple linear regression with rt-ECochG markedly improved upon correlations with residual hearing compared with the rt-ECochG-only model (rt-ECochG and 1-d 4PI model, R2 = 0.67; rt-ECochG and 3-mo 4PI model, R2 = 0.72; rt-ECochG-only model, R2 = 0.33). Both rt-ECochG and 4PI predict preservation of residual hearing after cochlear implantation. These findings suggest that the biological response of the cochlea to implantation, as reflected in 4PI, is an important determinant of residual hearing, independent of the acute effects on hearing during implant surgery seen with rt-ECochG. We speculate that 4PI relates to inflammation 1 day after implantation and fibrosis at 3 months.

KSR1 Knockout Mouse Model Demonstrates MAPK Pathway's Key Role in Cisplatin- and Noise-induced Hearing Loss.

Hearing loss is a major disability in everyday life and therapeutic interventions to protect hearing would benefit a large portion of the world population. Here we found that mice devoid of the protein kinase suppressor of RAS 1 (KSR1) in their tissues (germline KO mice) exhibit resistance to both cisplatin- and noise-induced permanent hearing loss compared with their wild-type KSR1 littermates. KSR1 is a scaffold protein that brings in proximity the mitogen-activated protein kinase (MAPK) proteins BRAF, MEK1/2 and ERK1/2 and assists in their activation through a phosphorylation cascade induced by both cisplatin and noise insults in the cochlear cells. KSR1, BRAF, MEK1/2, and ERK1/2 are all ubiquitously expressed in the cochlea. Deleting the KSR1 protein tempered down the MAPK phosphorylation cascade in the cochlear cells following both cisplatin and noise insults and conferred hearing protection of up to 30 dB SPL in three tested frequencies in male and female mice. Treatment with dabrafenib, an FDA-approved oral BRAF inhibitor, protected male and female KSR1 wild-type mice from both cisplatin- and noise-induced hearing loss. Dabrafenib treatment did not enhance the protection of KO KSR1 mice, providing evidence dabrafenib works primarily through the MAPK pathway. Thus, either elimination of the KSR1 gene expression or drug inhibition of the MAPK cellular pathway in mice resulted in profound protection from both cisplatin- and noise-induced hearing loss. Inhibition of the MAPK pathway, a cellular pathway that responds to damage in the cochlear cells, can prove a valuable strategy to protect and treat hearing loss.

Superparamagnetic iron oxide nanoparticle regulates microbiota-gut-inner ear axis for hearing protection.

Noise-induced hearing loss (NIHL) is a highly prevalent form of sensorineural hearing damage that has significant negative effects on individuals of all ages and there are no effective drugs approved by the US Food and Drug Administration. In this study, we unveil the potential of superparamagnetic iron oxide nanoparticle assembly (SPIOCA) to reshape the dysbiosis of gut microbiota for treating NIHL. This modulation inhibits intestinal inflammation and oxidative stress responses, protecting the integrity of the intestinal barrier. Consequently, it reduces the transportation of pathogens and inflammatory factors from the bloodstream to the cochlea. Additionally, gut microbiota-modulated SPIOCA-induced metabolic reprogramming in the gut-inner ear axis mainly depends on the regulation of the sphingolipid metabolic pathway, which further contributes to the restoration of hearing function. Our study confirms the role of the microbiota-gut-inner ear axis in NIHL and provides a novel alternative for the treatment of NIHL and other microbiota dysbiosis-related diseases.

Evaluation of a multi-function in-ear device performance in the presence of impulse noise using acoustic test fixtures

Real-time noise exposure monitoring has the potential to assess risk before damage occurs. We present on the development of an in- ear device that (1) provides hearing protection; (2) measures the noise in the ear canal to estimate exposure dose; and (3) monitors distortion product otoacoustic emissions (DPOAE) over time. To validate the device’s ability to measure impulse noise under hearing protection, we measured the response in a field test. A single AR15 was shot multiple times, and four prototypes were used in multiple acoustic test fixtures (ATFs) at different relative distances from the exit of the gun. The ATFs included a G.R.A.S 45 CB in addition to a head simulator designed to detect both air- and bone-conducted sound. We evaluated the impulse peak insertion loss (IPIL) metric of the device inserted by itself or in combination with other hearing protection (“double protection” condition) to assess attenuation of impulsive noises. We also compared the device's microphone measurements to those obtained through the ATF microphones, and to the recordings of external microphones located at or near the ear of each ATF. Results demonstrate the value of testing in-ear devices in acoustic test fixtures during development phases.

Protection exhibited by hearing protection devices using test fixtures under extended shock tube exposure ranges

Hearing protection devices (HPDs) are used in a variety of environments to mitigate the risk of hearing injury, particularly in environments with pervasive impulsive noise. Evaluation of HPD performance for these conditions can be performed with acoustic test fixtures to ensure human subjects are not exposed to injurious levels of noise. Impulse Peak Insertion Loss (IPIL) and Impulse Spectral Insertion Loss (ISIL), as defined in ASA/ANSI S12.42, are used to quantify and compare performance of HPDs in exposure environments created by different impulsive sources. To simulate a range of exposures relevant across industries, multiple shock tubes were used to generate waveforms with A-durations ranging from 0.1 to 6.0 ms and peak pressures ranging from 130 to 183 dB. Protection provided by each device varied depending on the source conditions with passive and active devices producing fundamentally different responses depending on source characteristics. Ultimately, evaluation of devices under a variety of impulsive noise conditions allows for a more representative evaluation of HPD performance, bridging the gap between standard testing protocols and real-world acoustic environments, thus enabling better informed HPD selection.

Measuring hearing protector attenuation of impulse noise on acoustic test fixtures using maximum A-weighted energy reduction

Hearing protection devices (HPDs) and firearm suppressors can help mitigate risk of hearing loss from small caliber firearms. ANSI S12.42 is the standard for measuring HPD impulse peak insertion loss (IPIL). No consensus standard exists for measuring firearm suppressor noise reduction, though the industry is working toward a standard using maximum accumulated A-weighted energy. A common attenuation metric for different impulse noise reduction technologies would inform the individual and combined impact of these technologies. The maximum A-weighted energy reduction for several HPDs was assessed using firearm impulses from two rifles (0.300 Winchester Magnum and 5.56x45) with two ATFs and five field microphones positioned on opposite sides of the gun at four locations (field levels between 180- and 140-dB pSPL). No adjustments were made to account for tissue/bone conduction. Maximum A-weighted energy reduction values for single protection ranged between 17 dB (earmuff with safety glasses) and 43 dB (preformed earplug). Similar to IPIL, maximum A-weighted energy reduction increased with increased impulse levels. Advantages, disadvantages, and technical issues associated with the procedure will be discussed.

Design and evaluation of a noise dosimeter integrated into an ear-muff hearing protector

In impulse-noise environments, such as during weapons training, it can be difficult to characterize an individual’s true cumulative exposure, and consequently their risk of hearing loss. Direct measurements of sound pressure in the ear canal underneath hearing protection are ideal for assessing the protected noise exposure because the effects of distance, orientation, protection, etc., are automatically included in the measurement. However, these types of measurements are not commonly collected outside the laboratory. In this research, we develop and evaluate a portable a noise dosimeter that is integrated into a commonly used muff-based hearing protector (3M™ PELTOR™ ComTac™ V). The design of the device aims to simultaneously measure both the external and the under-the-muff sound pressures in a portable, wearable form-factor. First, we demonstrate that the modifications do not affect the hearing protector attenuation using an acoustic test fixture and a fit-check system across 10 refits (p = 0.14). Next, we show through testing with a shock-tube and acoustic test fixture that it is possible to obtain valid pressure measurements through this system. Finally, we report on initial field testing during weapons training. Future application of this technology can be used to develop damage risk criteria based on in-ear measurements that will provide for more accurate individualized risk assessment.

Comparison of two acoustic test fixtures for measuring impulse level dependent attenuation

In the American National Standards Institute (ANSI) S12.42-2010 standard for measuring insertion loss of hearing protection devices (HPDs) in impulsive noise, the range of peak sound pressure levels for the impulses is 132 to 168 dB peak sound pressure level (dB pSPL). The specification of the acoustic test fixtures (ATFs) included an IEC 60318-4 ear simulator fitted with a microphone. The microphones typically used are a ¼” cartridge and have a dynamic range up to about 169 dB pSPL. For most small caliber firearms, the peak SPLs are less than 170 dB SPL at the location of the shooters ear (Schulz et al. 2013). For some military weapon systems that produce impulses greater than 170 dB pSPL, impulse insertion loss cannot be assessed without exceeding the microphone maximum dynamic range. Some condenser microphones have maximum dynamic ranges of 190 dB pSPL. This paper compares insertion losses for HPDs measured on two GRAS 45CB ATFs with microphones with maximum dynamic ranges of 169 and 193 dB pSPL. Waveform distortion, field probe to unoccluded transfer functions between the ATF and field probe will be examined for distortion and accuracy when estimating the impulse level dependent attenuation.

Influence of reference transducer location on hearing protector attenuation metrics for impulse noise

The ANSI/ASA S12.42-2010 standard can be used to estimate the attenuation for impulsive noises between 130 and 170 decibels peak sound pressure level (dB pSPL). The ANSI/ASA S12.42 method uses a complex transfer function between the signal received in the ear of an acoustic test fixture (ATF) and a reference transducer. The reference transducer is at the same radial distance from the impulse source and at less than 30 degrees from the ATF angle. The reference transducer is specified as a pencil-type pressure (> 40.6 cm long). The maximum angle and the minimum pencil probe dimensions could be incompatible near the source, or may introduce artifacts or hazards. In this study, several hearing protectors were evaluated with two rifles (A-Bolt .300 Winchester Magnum and Colt AR-15 5.56 caliber), two ATFs (GRAS 45CB), and five transducers (four ¼” microphones and one surface mount microphone). The ATFs were on opposite sides of the gun at distances for field levels between 180- and 140-dB pSPL. For each location and rifle, S12.42 metrics were calculated for all 20 combinations of ATF ear and reference transducer. Results indicated that S12.42 metrics were minimally affected by the locations of the reference transducers.

Highlights from the technical committee on noise

The Technical Committee on Noise (TCNS) includes researchers and industry practitioners interested in understanding noise generation from a variety of sources, its propagation, and its impact on structures, objects, and people. The goal of reducing the impact of this noise, or unwanted sound, has led to innovative model development, measurement techniques, mitigation strategies, and input towards the establishment of regulations. Community noise definition and abatement is of particular interest and motivates the advancement of research on a variety of topics, such as transportation noise from traditional and new vehicles, hearing protection, jet and rocket noise, building systems noise and vibration, atmospheric sound propagation, soundscapes, and low-frequency sound. The diverse technical background of TCNS members is essential, given the interdisciplinary nature of this research, and it is mirrored in the topics of special sessions typically held jointly with other ASA technical committees.

Improving speech understanding for face-to-face communication in noise when wearing hearing protectors

Active hearing protection devices (eHPDs) are commercially available that enhance communication at low noise levels by amplifying both speech and noise. A study has been performed to develop algorithms for improving face-to-face speech communication in both low- and high-level noises when wearing eHPDs. The (mixed) environmental noise and speech at frequencies from 200 to 6000 Hz are divided into 16 or 24 contiguous subbands corresponding to 1.5 and 1 times the bandwidth of auditory filters, respectively. Signals are processed in the time domain with the overall group delay intended to maintain synchronization between speech and lip movements. The temporal modulation in each subband is band-limited to 2–16 Hz using zero time delay, moving detrend, high-pass, and moving average low-pass filters. This modulation is compared to the normalized unfiltered modulation in the subband to provide an estimate of the speech signal-to-noise ratio (eSNR). A threshold is selected for the eSNR above which time signals in subbands are combined to produce the instantaneous output and below which subband signals are attenuated. Subjects “wearing” a simulated HPD and listening to speech in industrial noise experience, on average, a 12% increase in intelligibility when using the algorithm. [Work supported by NIOSH and the Alpha Foundation.]

Effect of shooting glasses on earmuff attenuation measured with an acoustic test fixture for gunfire impulses

The EPA requirement for hearing protector labels is based on the decrepit ANSI S3.19-1974 standard, which prohibits the use of eyewear during the REAT testing that leads to the NRR on the product label. Firearm users are recommended to wear protective eyewear while shooting. In this presentation, we review past work regarding the effects of eyewear on earmuff performance and present results from five samples of one product that includes both eyewear and an earmuff. Impulses ranging between 139 and 178 dB peak SPL were used. Impulse Insertion Loss was less than 10 dB below 400 Hz for earmuffs alone and negligible for the earmuff and glasses condition and attenuation in the high frequencies was reduced by approximately 15 to 25 dB. Impulse peak insertion loss values per ANSI S12.42 were reduced from 21 to 39 dB for the earmuff alone to 15 to 22 dB when eye protection was added. Hearing conservation programs need to account for the deleterious effect of protective eyewear on earmuffs, and additional studies with broad combinations of earmuffs and eyewear are needed to establish the range over which eyewear can be expected to compromise earmuff attenuation.

Development of a biofidelic acoustic test fixture and evaluation in impulsive noise

Here, we describe the development and use of a novel biofiedlic head surrogate for evaluating head and hearing protection devices against impulsive, shock, and blast insults. The head surrogate, derived from biomedical imagery, includes biofidelic pinnea, ear canals, and skull. In addition to microphones positioned at the ear canal terminus, the surrogate includes accelerometers and a hydrophone to provide an estimate of sound propagation through the bone-conduction pathways. This allows use of the surrogate to estimate a device's ability to attenuate bone-conducted pressure waves. We discuss the tradeoffs between biofidelity, manufacturability, instrumentation, and cost. We will show example data from various test campaigns, including the estimating the attenuation of the bone-conduction pathway afforded by different helmet systems during a 178 dB SPL (peak) shock insult. We will conclude with a look towards the future, including potentially updating the underlying three dimensional models to align with modern biomedical models and databases.

Immersive auditory awareness: A smart earphones platform for education on noise-induced hearing risks

The Audio Research Platform developed by the ÉTS-EERS Industrial Research Chair in In-Ear technologies is a digital audio processing wearable device that features a powerful Digital Signal Processor and a pair of wired earplugs featuring outer- and inner-ear microphones as well as miniaturize loudspeaker. ARP has been used since over the last 2 decades by CRITIAS to develop new algorithms for advanced hearing protection and communication in noise, as well as in-ear audio sensing. In this adaptation, the ARP enables transparent hearing of ambient sounds, simulates varying degrees of hearing loss, and includes a tinnitus simulator. ARP also functions as a personal music player, monitoring playback levels and displaying the “Age of your ears”) a metric recently proposed by CRITIAS), predicting accelerated auditory aging from excessive music playback. In the playback mode, wearers experience pre-recorded noise, prompting vocal adjustments known as the “Lombard Effect.” ARP analyzes the wearer's voice using the outer-ear microphone, illustrating level and pitch shifts in speech due to a noisy environment. This paper details ARP's technical aspects, positioning it as a powerful tool to inform the public about noise-induced hearing loss and promote awareness and prevention through enjoyable real-time demonstrations.

PROFILE OF RISK FACTORS FOR ACOUSTIC TRAUMA IN 105 HOWITZER CANNON SHOOTER STUDENTS AT THE PUSAT PENDIDIKAN ARTILERI MEDAN-CIMAHI

Acoustic Trauma is hearing loss caused by short period high frequency noise. Hearing loss can occur in military, because it uses the main tools of the weaponry system, such as guns, military vehicles, and explosions. This research aims to determine the description of risk factors for acoustic trauma, patterns of hearing protector use, and ear complaints among students of Pusdik Armed who perform 105 Howitzer Cannon shooting practice. This study used a descriptive method with a cross sectional design on the students of Pusdik Armed who perform 105 Howitzer Cannon shooting practice. The sampling technique used total sampling with 103 population. The research instrument was secondary data from the public dedication questionnaire of Dr Asti Kristianti, Sp.THT-BKL, M.Kes. The results showed a description of the risk factors for acoustic trauma in Pusdik Armed Students who perform Howitzer 105 Cannon shooting practice mostly due to high noise exposure (64.1%), smoking history (60.2%), using PLDs (59.2%), a minority do not wear hearing protectors (12.6%), and the use of ototoxic drugs (1.9%), and no one has hypertension and a family history of hearing loss. The pattern of using hearing protectors during 105 Howitzer Cannon shooting practice is from students who use ear protectors (87.4%), some use ear protectors during training (72.8%). The description of ear complaints before doing Howitzer 105 Cannon shooting practice mostly did not experience ear complaints either before (82.5%) or after (76.6%). Therefore, it is necessary to require the use of ear protective equipment for cannon shooters.

Strategies of Hearing Preservation With Military Personnel: A Scoping Review.

The purpose of this study was to map the strategies used in hearing health education with military personnel during the Hearing Preservation Program (HPP). This study is a scoping review, with electronic searches conducted in online databases and gray literature: Latin American and Caribbean Literature in Health Sciences, PubMed/Medline, Scopus, Web of Science, ASHAWire, Google Scholar, and ProQuest Dissertation & Theses. Only studies describing, analyzing, or evaluating the application of the HPP to active duty or training military personnel were included. A total of 3,478 references were retrieved, and 12 studies met the inclusion criteria. The strategies were classified into five categories: focus group aimed at exploring knowledge and perceptions regarding hearing health (five studies), training on the proper fitting of hearing protection devices (four studies), the utilization of audiovisual materials (seven studies), questionnaires administrated before and after educational intervention (five studies), and feedback survey concerning the implemented hearing health education (three studies). There are five strategies that aimed at assessing knowledge and attitudes, improving hearing health education, facilitating information access, and evaluating the applied actions. https://doi.org/10.23641/asha.25219589.

A Simulation Study of Noise Exposure in Sledge-Based Cable Yarding Operations

Ensuring the safety of forestry workers is a key challenge, particularly when working with partly mechanized harvesting systems. Cable yarding is typically used in steep terrain timber harvesting. For long-distance extraction, one of the few alternatives is to use sledge yarders, but these machines may expose workers to high doses of noise. The goal of this study was to model haulers’ exposure to noise in sledge-based cable yarding operations, based on a simulation approach that considered variable factors such as the yarding distance, lateral yarding distance, and average skyline height. Taken into consideration were 165 scenarios developed by examining the variation in yarding distance (500 to 1500 m, with a step of 100 m), lateral yarding distance (10 to 50 m, with a step of 10 m), and average skyline height above the ground (10, 15, and 20 m). The simulations assumed an 8-h working day with a break of 1 h. The models and statistics published by other studies were used to calculate the time consumption and number of work cycles completed within a working day. These data were used to compute the equivalent exposure to noise (LAeq) for each scenario, as well as for those work elements that were likely to expose the haulers to noise the most. The presented findings indicated that (i) the exposure to noise was higher than 100 dB(A), irrespective of variation in the considered factors; (ii) the trend in exposure was characterized by polynomials in relation to the extraction distance, and the magnitude of exposure was consistently affected by variation in the considered factors; and (iii) without hearing protection, the empty and loaded turns exposed workers to noise over the permissible limits. These findings strongly suggest the use of hearing protection when working in close proximity to sledge-based cable yarding operations. The methods proposed in this study in the form of simulation may help benchmark other forest operations.

Gelatin-Encapsulated Tetrahedral DNA Nanostructure Enhances Cellular Internalization for Treating Noise-Induced Hearing Loss.

Nanoparticle-based drug delivery strategies have emerged as a crucial avenue for comprehensive sensorineural hearing loss treatment. Nevertheless, developing therapy vectors crossing both biological and cellular barriers has encountered significant challenges deriving from various external factors. Herein, the rational integration of gelatin nanoparticles (GNPs) with tetrahedral DNA nanostructures (TDNs) to engineer a distinct drug-delivery nanosystem (designed as TDN@GNP) efficiently enhances the biological permeability and cellular internalization, further resolving the dilemma of noise-induced hearing loss via loading epigallocatechin gallate (EGCG) with anti-lipid peroxidation property. Rationally engineering of TDN@GNP demonstrates dramatic alterations in the physicochemical key parameters of TDNs that are pivotal in cell-particle interactions and promote cellular uptake through multiple endocytic pathways. Furthermore, the EGCG-loaded nanosystem (TDN-EGCG@GNP) facilitates efficient inner ear drug delivery by superior permeability through the biological barrier (round window membrane), maintaining high drug concentration within the inner ear. The TDN-EGCG@GNP actively overcomes the cell membrane, exhibiting hearing protection from noise insults via reduced lipid peroxidation in outer hair cells and spiral ganglion neurons. This work exemplifies how integrating diverse vector functionalities can overcome biological and cellular barriers in the inner ear, offering promising applications for inner ear disorders.

Noise Exposure, Prevention, and Control in Agriculture and Forestry: A Scoping Review

Noise is a major physical hazard in agricultural activities, and numerous research activities have managed to detect its effects, resulting in surveys and measurements which help to define exposure limits, prevention methods, and control strategies. This review aims to collect and analyse the data from research studies and to provide a comprehensive overview on the subject. Thus, a set of 81 papers, gathered from the Scopus and PubMed scientific databases, has been analysed to provide information regarding the evolution of noise exposure levels over time, to highlight findings on noise-induced hearing loss (NIHL), and to list strategies for noise prevention and control in agriculture. Bibliographic research showed that noise measurements between 1991 and 2022, included in scientific research on farming, forestry, and animal husbandry, mainly reported values beyond the threshold of 85 dB(A); furthermore, several research activities on NIHL showed that farmers’ family members and children are often exposed to high levels of noise. Lastly, an analysis of the prevention and control strategies over time is provided, focusing on prevention programmes, screening, and the use of hearing protection devices (HPD). The identified literature suggests that additional efforts are required in regards to machinery design relating to the socio-technical aspects of agricultural activities and that side-effects of NIHL, as well as the negative impact of noise on other risks, might deserve further investigation.

Study on the fit testing for the workers wearing hearing protection device in machinery manufacturing enterprises

Objective: To investigate the occupational noise hazards in five machinery manufacturing enterprises, and to evaluate the individual noise reduction values and influencing factors of workers wearing hearing protection device (HPD) by individual fit testing. Methods: From November 2021 to January 2022, 5 machinery manufacturing enterprises in Bao'an District of Shenzhen were selected to conduct an occupational health survey to understand the noise exposure level of workers. The 3MTM E-A-RfitTM fitness test system was used to test the baseline individual sound attenuation value level (PAR) of the daily wear of the ear protecters for 485 workers in typical noise working positions. Workers whose PAR values could not meet the requirements of noise reduction at work were instructed to wear and repeated tests were conducted. PAR results of the workers before and after the intervention were collected and analyzed. Results: The noise workers who received the suitability test were mainly distributed in 24 types of work, the job noise exposure level was 80.2 dB (A) ~ 95.0 dB (A), and the job noise excess rate was 52.5% (138/263). The median baseline PAR [M (Q(1), Q(3)) ] for 485 workers was 6.0 (0.0, 14.0) dB. The baseline PAR of male workers, those with more than 15 years of working experience, those with more than 15 years of using ear guards, those who considered ear guards comfortable to wear, those with college degree or above, and those exposed to noise level 90 dB (A) were higher, and the difference was statistically significant (P<0.05). A total of 275 workers (56.7%) did not pass the baseline PAR test, and there was no statistically significant difference in the intervention rate of workers in different noise groups (P>0.05). PAR in subjects who did not pass baseline after intervention increased from 0.0 (0.0, 3.0) dB to 15.0 (12.0, 18.2) dB. Conclusion: The workplace noise hazard of machinery manufacturing enterprises is serious, and there is a great difference between the baseline PAR and the nominal value of the hearing guard worn by the noise exposed workers. The intervention measures can effectively improve the protective effect of wearing ear protectors.