Aliabadi et al., 2018 (Iran) |
Non-randomized before and after study |
Factory workers with different noise characteristics; two industrial factories in western Iran |
Intervention: workers wearing 5 types of earmuffs. Each protector sample was tested for 50 individuals and F-MIRE measurements were repeated three times. |
Difference in noise level outside vs. inside the protectors at low and high frequencies. |
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n = 50 (25 in each factory) |
Comparison: “Outside” vs. “Inside” the hearing protection device (HPD). |
The attenuation values of hearing protectors were lower than those of the laboratory noise reduction classifications (p <0.05) for workers exposed to low-frequency noise; and higher for workers exposed to high-frequency noise (p <0.05). |
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Conclusion: (-) high risk |
Behar et al., 2018 (Canada) |
Non-randomized before and after study |
Musicians in an orchestra; Toronto orchestra pit (Four Seasons Center) n = 3 |
Intervention: engineering noise control. Two acoustic shells were evaluated at the same time - two dosimeters in each shell (front and back - the difference was expressed in “attenuation”) - 45º in front of the musician. One instrument at a time. Two tests for each instrument. |
Total attenuation: 9.2 dBA (Manhasset shell) and 5.9 dBA (Wenger shell) (p-value = 0.006). |
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Comparison: “front” vs. “behind” the shell. |
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Conclusion: (-) high risk |
Biabani et al., 2017 (Iran) |
Non-randomized before and after study |
Workers of different occupations exposed to noise in work environment; Hamadan University of Medical Sciences laboratory |
Intervention: workers wearing 3 types of earmuffs. Each protector sample was tested for 30 individuals and the MIRE measurements were repeated three times. |
Typical safety goggles can reduce average PAR by approximately 2.5 dB (p <0.05). The variability in PAR values between individuals, intra-individuals, and between hearing protectors was not statistically significant (p> 0.05). |
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n = 30 |
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Comparison: with and without goggles. |
Conclusion: (-) high risk |
Bourchom et al., 2018 (Thailand) |
Randomized clinical trial |
Thai military service recruits randomly assigned to 2 groups: not wearing hearing protection and using silicone protectors; military shooting training |
Intervention: use of HPD. |
Immediately after the shooting, those who did not wear hearing protection had a higher rate of SNHL than the other group, at high frequency (53.2% vs. 0%, p <0.05). On the 3rd day, hearing thresholds were gradually improved at all frequencies, except 6,000 Hz. On the 7th day, three recruits (10%) from the group without hearing protection still had SNHL on the audiogram, 12 individuals (40%) had abnormal function of external hair cells detected by DPOAEs. |
+/?/-/-/+/+/? |
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n = 60 |
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Control: workers who have not used HPD. |
Conclusion: (+) low risk |
Collée et al., 2019 (Belgium) |
Non-randomized before and after study |
Military personnel from the Belgian military service; Occupational Medicine Service and Belgian Defense Medical Expertise Center. |
Intervention: hearing conservation program (HPC). |
For each annual increment, average hearing thresholds at 3, 4, and 6 kHz increased by 0.08 dB and this number decreased (was less positive) by 0.18 dB per year. |
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n = 18,672 |
Control: before HCP implementation. |
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Conclusion: (-) high risk |
Fallah Madvari et al., 2019 (Iran) |
Non-randomized before and after study |
Workers of different occupations exposed to noise; tile industry |
Intervention: training with the BASNEF Education Model (n = 50). |
Before intervention, the time of use of HPD in both groups was 0.5 hours and noise exposure was 89 dBA. After intervention, the time of using HPD increased in the intervention group, noise exposure was 80 dBA, and for the control group, without training, the same amount of time using HPD resulted in 89 dBA of exposure. |
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n = 100 |
Control: untrained colleagues (n = 50). |
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Conclusion: (-) high risk |
Frederiksen et al., 2017 (Denmark) |
Non-randomized before and after study |
Workers of different occupations exposed to noise; |
Intervention: hearing conservation program (HCP). |
Average noise levels decreased from 83.9 dBA to 82.8 dBA. For workers exposed to more than 85 dBA, use of HPD increased from 70.1 to 76.1%. |
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11 Danish industries with high noise levels |
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n = 271 |
Control: before HCP implementation. |
Conclusion: (-) high risk |
Gong et al., 2019 (China) |
Non-randomized before and after study |
Workers of different occupations exposed to noise; four factories in eastern China |
Intervention: training for the proper fitting of HPD. |
Significant improvement was shown in post-intervention PARs (p <0.05), as well as PARs from the follow-up visit (p <0.05). Comparing follow-up visit PARs to post-intervention PARs, good sustainability was demonstrated in two factories (p> 0.05), while a significant decline (p <0.05) was observed in another. |
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n = 335 |
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Comparison: pre-intervention, post-intervention, and six-month follow-up. |
Conclusion: (-) high risk |
Khairai et al., 2018 (Malaysia) |
Non-randomized before and after study |
Case study; CNC industry |
Intervention: engineering control to reduce noise in the CNC stripping process. |
Initial average noise level with all machines turned off was 95.8 dBA. After the leaking pneumatic system was resolved, noise was reduced to 55.52 dBA. Average noise level with all machines in operation was 109.34 dBA. After six machines were brought together in one area and it was covered with a plastic curtain, noise was reduced to 95.21 dBA. |
-/-/-/-/+/+/? |
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Comparison: Before and after improvements. |
Conclusion: (-) high risk |
Neitzel et al., 2018 (Sweden) |
Interrupted time series |
Four Swedish paper towel factories; |
Intervention: hearing conservation program (HCP). |
Noise levels have decreased in Swedish paper factories over time. Results of the focus group indicated that use of HPD increased over time. Approximately 50% of workers in the four factories evaluated were exposed to a limit equal to or greater than 8h of noise exposure of 85 dBA at the end of the study period in 2010. |
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n = 1,157 areas |
Control: before HCP implementation. |
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Conclusion: (-) high risk |
Liu et al., 2018 (China) |
Non-randomized before and after study |
Workers of different occupations exposed to noise; Chinese textile factory; |
Intervention: training for the proper fitting of HPD. |
Immediate and residual effects of training obtained by workers in the attenuation of HPD were observed and also effects of training in improving attenuation after a period of daily use. |
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N = 189 |
Comparison: pre-intervention, post-intervention, and follow-up for six and twelve months. |
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Conclusion: (-) high risk |
Murphy et al., 2018 (United States of America) |
Non-randomized before and after study |
Four firearms; outdoor shooting center (Rose Lake) and hunting field (Rudyard) |
Intervention: engineering control for noise reduction (firearm noise suppressor) and administrative control (low-speed ammunition). |
Firearm noise suppressors tend to reduce peak sound pressure in the sniper’s ears by 17–26 dB, reduce equivalent energy levels by 9–21 dB, and reduce overall sound pressure level by 2–23 dB. Levels of the unexpressed Savage rifle showed a difference of 1 to 2 dB depending on the ammunition, while Remington rifles had between 12 dB and a difference of 20 dB between the two ammunition speeds. |
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N = 5 shootings |
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Comparison: Before and after improvements. |
Conclusion: (-) high risk |
Prieve et al., 2017 (United States of America) |
Non-randomized before and after study |
Different compressed air guns; ten areas for manufacturing research and development environments |
Intervention: engineering control for noise reduction (advanced air guns with noise suppression). |
17 of 21 comparisons of advanced air guns with conventional air guns exhibited statistically significant noise level reductions ranging from 3.3 to 17.7 dBA, while only three comparisons showed significant increases, the largest being 1.8 dBA. Advanced noise-reducing air guns engineering controls can be highly effective to reduce exposure to occupational noise. |
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n = 11 |
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Comparison: conventional air guns. |
Conclusion: (-) high risk |
Roberts et al., 2017 (United States of America) |
Non-randomized before and after study |
Noise dosimetry measures from 1979 to 2014; |
Implementation of the review of the MSHA noise regulation in 2000. |
Global noise levels in mines have decreased. However, this decrease was not uniform across all mining sectors. |
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Mining Health and Safety Administration |
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n = more than 700,000 |
Conclusion: (-) high risk |
Saleh et al., 2017 (United States of America) |
Non-randomized before and after study |
Heavy equipment (roller, crane, and motor grader); International Union of Operating Engineers training center |
Intervention: engineering control to reduce noise. |
SPLs inside the cabins of the heavy equipment operator were significantly reduced by 5.6 - 7.6 dBA in the maximum acceleration configuration after installing the SDMats (p <0.01). |
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n = 3 |
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Comparison: Before and after installing sound-damping mats (SDMats). |
Conclusion: (-) high risk |
Sayler et al., 2017 (United States of America) |
Non-randomized before and after study |
Metal fabrication facilities operated by a single company; |
Intervention: hearing conservation program (HCP). |
Higher expenditures for training and HPD fitting tests were significantly associated with a reduction in the prevalence of PTS. Higher expenditure on training was also related to a lower prevalence of hearing loss and rates of high-frequency hearing loss. |
-/-/-/-/+/+/? |
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n = 14 |
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Control: before implementation of the hearing conservation program (relating cost and effectiveness). |
Conclusion: (-) high risk |
Tanas et al., 2018 (Poland) |
Non-randomized before and after study |
Case study - Grain crusher; grain crusher operator workstation |
Intervention: engineering control for noise reduction in a grain crusher. |
The structural modifications introduced reduced noise level by 3 dBA for the frequencies of the hopper component related to vibration of the hopper (180 Hz) and support structure of the crusher (240 to 480 Hz). The level of these components determines the noise level at the operator's workstation for the average grain filling conditions. Total noise level in the shredder operator has been reduced by 2.6 dBA. |
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Comparison: Before and after improvements. |
Conclusion: (-) high risk |