U.S. automobile and light duty motor vehicle manufacturing recorded 17.0 hearing loss illness cases per 10,000 full-time workers in 2024, roughly 15 times the private-industry rate of 1.1 (BLS Survey of Occupational Injuries and Illnesses, Table SNR08 2024; 17.0 divided by 1.1 is about 15.5). The noise behind those cases is not just loud, it is spiky: auto workers in a Chinese cohort had a median kurtosis, a measure of how impulsive a noise is, of 15.0 against 5.1 in textile mills (Shi et al., Frontiers in Psychology 2022). In five Zhejiang auto plants, 73.6% of workers were exposed to this non-steady noise and 32.6% had high-frequency hearing loss (Wang et al., Journal of Environmental and Occupational Medicine 2022), while an air impact wrench in a training workshop reached a maximum A-weighted level of 93.6 dB (Abdul Rahim et al., IJERPH 2022). We aggregated data from the Bureau of Labor Statistics, OSHA, NIOSH, the EU noise directive, Atlas Copco technical documentation, and peer-reviewed field studies from the U.S., China, Korea and Malaysia. Our manufacturing noise exposure statistics cover factory noise in general; this roundup stays on the impact wrench, the pneumatic tool line and the impulsive bursts they create.
TL;DR
- 17.0 hearing loss cases per 10,000 workers in automobile and light vehicle manufacturing vs 1.1 in all private industry (BLS SOII 2024).
- 93.6 dB maximum A-weighted level for an air impact wrench in an automotive workshop (IJERPH 2022).
- 15.0 median kurtosis for 589 auto workers vs 5.1 for textile workers (Frontiers in Psychology 2022).
- 73.6% of 656 workers in five auto plants exposed to non-Gaussian, impulsive-type noise, and 32.6% with high-frequency hearing loss (JEOM 2022).
- 99 dB(A) declared sound power for a production impact wrench, a lab figure its maker says is not adequate for risk assessment (Atlas Copco W2410 documentation).
- 28.08 kurtosis threshold above which hearing loss risk rose at 80 to 100 dB(A) (JEOM 2025).
- 60% of tire-changing shift samples above the ACGIH 85 dBA limit, 0% above the OSHA limit (Annals of Work Exposures and Health 2021).
- 140 dB peak: the OSHA ceiling for impulsive or impact noise (OSHA 29 CFR 1910.95).
- 8 dB(A) quieter: oil-pulse vs double-hammer impact wrenches on auto assembly lines (JKSOEH 1995).
- 37.0% of 200 tyre shop workers with neurological hand-arm vibration symptoms (Journal of Occupational Health 2019).
1. Hearing Loss Case Rates in Vehicle Manufacturing
Automobile and light duty motor vehicle manufacturing logged 17.0 recordable hearing loss cases per 10,000 full-time workers in 2024, more than double the 7.2 rate for manufacturing overall. These are illness cases that employers recorded on their injury and illness logs, not the results of a population hearing survey. Under OSHA’s noise standard, plant hearing tests compare each worker with a baseline audiogram to flag a standard threshold shift, a measured drop in hearing since that first test.
The table cannot say how much of that toll comes from impact wrenches rather than presses, welding or conveyors. Metal stamping, a press-driven process, sits even higher at 24.0, which is a reminder that a vehicle plant contains several impulsive sources at once. California’s state tables show far lower rates for the same sector, a gap the tables themselves do not explain; differences in industry mix are one possibility.
| Metric | Value | Source |
|---|---|---|
| Hearing loss cases per 10,000 full-time workers, automobile and light duty motor vehicle manufacturing (NAICS 33611), U.S. | 17.0 | BLS SOII Table SNR08, 2024 |
| Hearing loss cases per 10,000 full-time workers, motor vehicle metal stamping (NAICS 33637), U.S. | 24.0 | BLS SOII Table SNR08, 2024 |
| Hearing loss cases per 10,000 full-time workers, all transportation equipment manufacturing (NAICS 336), U.S. | 9.8 | BLS SOII Table SNR08, 2024 |
| Hearing loss cases per 10,000 full-time workers, all manufacturing, U.S. | 7.2 | BLS SOII Table SNR08, 2024 |
| Hearing loss cases per 10,000 full-time workers, all private industry, U.S. | 1.1 | BLS SOII Table SNR08, 2024 |
| Hearing loss cases per 10,000 full-time workers, transportation equipment manufacturing, California | 2.2 | California DIR, Occupational Injuries and Illnesses Table 8, 2024 |
| Hearing loss cases per 10,000 full-time workers, all manufacturing, California | 3.9 | California DIR Table 8, 2024 |
| Hearing loss cases per 10,000 full-time workers, all private industry, California | 0.6 | California DIR Table 8, 2024 |
Context note: in the same national table, the total illness rate for automobile and light duty motor vehicle manufacturing was 141.3 per 10,000 workers, so hearing loss is one category among several; most of that total (120.2) falls in the “all other illnesses” column. Rates are calculated per 20,000,000 hours worked, the equivalent of 10,000 full-time workers.
2. How Loud Impact Wrenches and Air Tools Really Are
An air impact wrench in a Malaysian automotive training workshop reached a maximum A-weighted level of 93.6 dB, with a 95% confidence interval of 90.4 to 96.9 dB (Abdul Rahim et al., International Journal of Environmental Research and Public Health 2022). That sits well above the 85 dBA level at which NIOSH considers noise hazardous (NIOSH 2026). Lmax here means the highest A-weighted level the meter registered, not the true instantaneous peak of the sound wave, which is higher.
Manufacturer figures come from a standard test, not a busy line, and can run lower. Atlas Copco declares 88 dB(A) of sound pressure for its W2410 impact wrench and states that declared values “are not adequate for use in risk assessments” and that workplace values may be higher (Atlas Copco W2410 Safety and Product Information). Load matters too: the same air ratchet was more than 10 dB louder when attaching a wheel than when removing one.
| Metric | Value | Source |
|---|---|---|
| Air impact wrench, maximum A-weighted level (Lmax), automotive maintenance workshop | 93.6 dB (95% CI 90.4 to 96.9) | Abdul Rahim et al., IJERPH 2022 |
| Angle grinder, maximum A-weighted level, same automotive workshop | 92.0 dB | Abdul Rahim et al., IJERPH 2022 |
| Air compressor, maximum A-weighted level, same automotive workshop | 88.9 dB | Abdul Rahim et al., IJERPH 2022 |
| Atlas Copco W2410 impact wrench, declared sound pressure level (ISO 15744) | 88 dB(A), uncertainty 3 dB(A) | Atlas Copco W2410 product documentation (accessed October 2026) |
| Atlas Copco W2410 impact wrench, declared sound power level | 99 dB(A), uncertainty 3 dB(A) | Atlas Copco W2410 product documentation (accessed October 2026) |
| Air ratchet attaching a wheel vs removing a wheel, measured 2 ft from the tool | 86.9 dBA vs 75.9 dBA | Willson-Kerns and Brazile, Annals of Work Exposures and Health 2021 |
| Compressed-air blow-off guns and air wands | 90 to 115 dBA | OSHA Technical Manual, Section III Chapter 5 |
Outlier note: the OSHA Technical Manual adds that the intensity of compressed-air noise is proportional to the 8th power of the air velocity, which is why OSHA’s control guidance centres on rerouting exhaust ports and avoiding higher line pressure. Most recent available data for the auto workshop tool survey: IJERPH, 2022.
3. Impulsiveness: The Kurtosis Profile of Auto Plants
Kurtosis is a statistic that describes the shape of a noise signal over time: a steady hum scores low, while a stream of sharp hammer blows scores high. Researchers call low-kurtosis noise “Gaussian” (steady) and high-kurtosis noise “non-Gaussian” or “complex” noise. Auto workers in a Chinese cohort had a median kurtosis of 15.0, nearly three times the 5.1 recorded in textile mills (Shi et al., Frontiers in Psychology 2022).
What makes the auto profile distinctive is that its energy is not extreme. In a 2,898-worker Zhejiang sample, automobile workers averaged 88.43 dB(A) over eight hours, below textile workers at 93.02 dB(A), yet their mean kurtosis was 25.88 against 9.98 (Zhang et al., China CDC Weekly 2021). A weaving shed is loud and steady, as our textile mill loom noise statistics show; an assembly line is quieter on average and punctuated by bursts. An 8-hour average treats those two very differently from how the ear does.
| Metric | Value | Source |
|---|---|---|
| Median kurtosis (interquartile range), 589 automotive workers | 15.0 (9.1 to 25.1) | Shi et al., Frontiers in Psychology 2022 |
| Median kurtosis, 422 textile workers in the same study | 5.1 (3.3 to 11.2) | Shi et al., Frontiers in Psychology 2022 |
| 8-hour equivalent level (LAeq,8h), automotive workers | 87.7 ± 4.2 dB(A) | Shi et al., Frontiers in Psychology 2022 |
| Mean kurtosis, 996 automobile workers vs textile workers | 25.88 ± 37.38 vs 9.98 ± 9.28 | Zhang et al., China CDC Weekly 2021 |
| 8-hour equivalent level, automobile workers vs textile workers | 88.43 vs 93.02 dB(A) | Zhang et al., China CDC Weekly 2021 |
| Share of 656 workers in five auto plants exposed to non-Gaussian noise | 73.6% | Wang et al., JEOM 2022 |
| Peak sound pressure range across 14 impulsive U.S. manufacturing sites (bottling to drop forging) | 108.8 to 134.4 dB | Erdreich, Journal of the Acoustical Society of America 1986 |
Context note: the Erdreich study, held in the NIOSH collection, concluded that peak level alone could not classify impulse hazard and proposed kurtosis as the descriptor. Most recent available data for multi-site U.S. peak measurements: JASA, 1986.
4. Hearing Outcomes and Kurtosis-Adjusted Risk
In five Zhejiang automobile manufacturing plants, 32.6% of noise-exposed workers (214 of 656) had high-frequency noise-induced hearing loss, and kurtosis predicted it as strongly as decibels did: an odds ratio of 1.37 for each (Wang et al., Journal of Environmental and Occupational Medicine 2022). Speech-frequency loss, the range that matters most for everyday conversation, was far rarer at 6.7% (44 of 656), so most of the measured damage sits in the high-pitched range.
The modelling studies point the same way. When cumulative exposure is adjusted for kurtosis, the gap between workers exposed to impulsive and to steady noise shrinks sharply, which suggests the standard energy metric undercounts impulsive damage. A 2025 study put a number on the tipping point: within 80 to 100 dB(A), hearing loss risk rose once kurtosis passed 28.08 (Li et al., JEOM 2025). Set against the auto-plant kurtosis figures in section 3, many assembly workers sit close to that line, though the studies measured kurtosis in different samples and the spread within plants is wide.
| Metric | Value | Source |
|---|---|---|
| High-frequency noise-induced hearing loss, five auto plants | 32.6% (214 of 656) | Wang et al., JEOM 2022 |
| Odds ratio for high-frequency hearing loss, kurtosis | 1.37 (95% CI 1.14 to 1.63) | Wang et al., JEOM 2022 |
| Odds ratio for high-frequency hearing loss, 8-hour noise level | 1.37 (95% CI 1.08 to 1.76) | Wang et al., JEOM 2022 |
| High-frequency hearing loss prevalence, automobile workers in a six-industry sample | 24.4% | Zhang et al., China CDC Weekly 2021 |
| Gap in predicted hearing threshold shift, impulsive vs steady noise, before vs after kurtosis adjustment | 4.32 dB HL vs 1.63 dB HL | Shi et al., Frontiers in Psychology 2022 |
| Kurtosis level above which hearing loss risk rose, at 80 to 100 dB(A), 4,631 workers | 28.08 | Li et al., JEOM 2025 |
| Reduction in ISO 1999 underestimation of 3, 4 and 6 kHz threshold shift with A-weighted kurtosis adjustment, 973 workers | 7.20 dB HL | Liu et al., JEOM 2025 |
Context note: ISO 1999 is the international model that predicts hearing loss from noise energy and years of exposure. “dB HL” means decibels of hearing level on an audiogram. The 2025 threshold study is cross-sectional and its authors say the 28.08 value needs further verification.
5. Repair Shops and Tire Changers: Shift-Level Exposure
The same impact wrench follows the car out of the factory into collision shops and tire bays, where shift dosimetry has been published in more detail. At three U.S. tire-changing facilities, 60% of personal samples exceeded the ACGIH limit of 85 dBA, yet none exceeded the OSHA permissible exposure limit (Willson-Kerns and Brazile, Annals of Work Exposures and Health 2021). The two answers come from the same shifts; the difference is the yardstick, since ACGIH uses an 85 dBA limit with a 3 dB exchange rate and OSHA a 90 dBA limit with a 5 dB rate.
The dosimetry logs also caught the bursts that an 8-hour average smooths away. For technicians who rely on earplugs through those bursts, real-world protection depends on fit, a gap covered in our hearing protection fit-testing statistics.
| Metric | Value | Source |
|---|---|---|
| Tire-changing shift samples above the ACGIH threshold limit value of 85 dBA | 60% (18 of 30) | Willson-Kerns and Brazile, Annals of Work Exposures and Health 2021 |
| Tire-changing shift samples at or above the OSHA action level | 3% (1 of 30) | Willson-Kerns and Brazile, Annals of Work Exposures and Health 2021 |
| Peak value reported in tire-shop dosimetry (impulses above 110 dB occurred numerous times) | 116 dBA | Willson-Kerns and Brazile, Annals of Work Exposures and Health 2021 |
| Average tire changes per technician shift (average shift 6 h 42 min) | 18 | Willson-Kerns and Brazile, Annals of Work Exposures and Health 2021 |
| Auto collision repair noise measurements above the ACGIH limit | 4 of 18 | Bejan, Brosseau and Parker, Journal of Occupational and Environmental Hygiene 2011 |
| Air guns, wrenches, cutoff wheels and air drills in collision shops: 5th percentile of measured levels | Above 90 dBA | Bejan et al., JOEH 2011 |
Context note: the collision-shop study ran during a low-production period, and its authors warn that technicians’ 8-hour exposures may exceed 85 dBA when the shops are busy. Most recent available data for U.S. collision repair shops: JOEH, 2011.
6. Peak Limits: What the Rules Actually Allow
Both OSHA and the EU directive cap impulse noise with a single peak number, and neither uses kurtosis. OSHA states that impulsive or impact noise “should not exceed 140 dB peak sound pressure level” (OSHA 29 CFR 1910.95). The tire-shop impulses in section 5, including a reported peak of 116 dBA, sit well below that ceiling, so a peak test alone would not flag them.
That leaves the 8-hour average to do the work, and section 4 shows why that is a weak fit for spiky noise. The EU directive is stricter on peaks, with action values starting at 135 dB(C), but it is still a peak test. The OSHA Technical Manual itself says impulsive or impact noises “are considered to be much more harmful to hearing than continuous noises”, a judgment the exposure math does not yet reflect.
| Metric | Value | Source |
|---|---|---|
| OSHA peak ceiling for impulsive or impact noise | 140 dB peak sound pressure level | OSHA 29 CFR 1910.95 |
| OSHA permissible exposure, 8 hours vs 15 minutes or less | 90 dBA vs 115 dBA | OSHA 29 CFR 1910.95, Table G-16 |
| OSHA action level that triggers a hearing conservation program | 85 dBA 8-hour TWA (50% dose) | OSHA 29 CFR 1910.95 |
| OSHA standard threshold shift: average change at 2,000, 3,000 and 4,000 Hz | 10 dB or more | OSHA 29 CFR 1910.95 |
| EU peak values: lower action, upper action, limit | 135, 137 and 140 dB(C) | EU Directive 2003/10/EC, Article 3 |
| EU daily exposure values: lower action, upper action, limit | 80, 85 and 87 dB(A) | EU Directive 2003/10/EC, Article 3 |
| U.S. workers exposed to hazardous noise at work each year | About 27 million | NIOSH, About Noise and Hearing Loss Prevention, 2026 |
Context note: “TWA” means time-weighted average, the 8-hour exposure average. “Dose” expresses the same exposure as a percentage of the allowed daily amount. NIOSH recommends 85 dBA averaged over an eight-hour workday as its exposure limit (NIOSH 2026).
7. Engineering Controls and Hand-Arm Vibration
The tool choice itself is the largest lever in the data. On Korean automobile assembly lines, oil-pulse impact wrenches were 8 dB(A) quieter than double-hammer wrenches (Jeung and Kim, Journal of Korean Society of Occupational and Environmental Hygiene 1995). An oil-pulse wrench delivers its torque through a hydraulic pulse unit rather than a metal hammer striking an anvil, and dominant hand vibration fell from 8.24 to 9.60 m/s2 for hammer tools to 2.59 to 3.23 m/s2. One trade-off: oil-pulse tools ran longer in total each day, because the stations using them fastened more bolts per cycle.
Redesigning a hammer-type tool helps far less. A NIOSH-collection study of an electric impact wrench got about 3 dBA from damping, a gasket and dual exhaust, and only about 2 dB at best from isolating the hammer impact (Markesino, Pruse and Rao, NOISE-CON 2004). Vibration is the second exposure from the same hammer action: it shakes the hands, and tyre shop workers with high daily vibration doses report far more nerve symptoms.
| Metric | Value | Source |
|---|---|---|
| Noise of oil-pulse vs double-hammer impact wrenches, automobile assembly lines | 8 dB(A) lower | Jeung and Kim, JKSOEH 1995 |
| Dominant hand-arm vibration, double-hammer wrench, right hand vs left hand | 8.24 vs 9.60 m/s2 | Jeung and Kim, JKSOEH 1995 |
| Dominant hand-arm vibration, oil-pulse wrench, right hand vs left hand | 2.59 vs 3.23 m/s2 | Jeung and Kim, JKSOEH 1995 |
| Noise reduction from combined damping, gasket and dual exhaust on an electric impact wrench | 3 dBA | Markesino et al., NOISE-CON 2004 |
| Atlas Copco W2410 impact wrench, declared vibration total value (ISO 28927-2) | 7 m/s2, uncertainty 2.8 | Atlas Copco W2410 product documentation (accessed October 2026) |
| Tyre shop workers with neurological vs vascular hand-arm vibration symptoms (200 workers) | 37.0% vs 12.5% | Qamruddin et al., Journal of Occupational Health 2019 |
| Neurological symptoms, high daily vibration dose (5 m/s2 or more) vs lower dose | 62.89% vs 12.62% | Qamruddin et al., Journal of Occupational Health 2019 |
Context note: most recent available data for the oil-pulse comparison on auto lines: JKSOEH, 1995; for the electric wrench redesign: NOISE-CON, 2004. Both predate today’s cordless and electronic tightening tools, so they show direction, not current fleet averages.
Summary: Automotive Assembly Impact Wrench Noise by the Numbers
| Metric | Value | Source |
|---|---|---|
| Hearing loss cases per 10,000 workers, automobile and light vehicle manufacturing vs all private industry | 17.0 vs 1.1 | BLS SOII Table SNR08, 2024 |
| Air impact wrench, maximum A-weighted level, automotive workshop | 93.6 dB | Abdul Rahim et al., IJERPH 2022 |
| Atlas Copco W2410 declared sound power level | 99 dB(A) | Atlas Copco W2410 product documentation |
| Median kurtosis, auto workers vs textile workers | 15.0 vs 5.1 | Shi et al., Frontiers in Psychology 2022 |
| Mean kurtosis, automobile workers, Zhejiang 2010 to 2019 | 25.88 | Zhang et al., China CDC Weekly 2021 |
| High-frequency hearing loss, five auto plants | 32.6% | Wang et al., JEOM 2022 |
| Odds ratio for high-frequency hearing loss, kurtosis | 1.37 (95% CI 1.14 to 1.63) | Wang et al., JEOM 2022 |
| Kurtosis risk threshold at 80 to 100 dB(A) | 28.08 | Li et al., JEOM 2025 |
| ISO 1999 underestimation corrected by A-weighted kurtosis adjustment | 7.20 dB HL | Liu et al., JEOM 2025 |
| Tire-changing shift samples above the ACGIH 85 dBA limit | 60% | Willson-Kerns and Brazile, AWEH 2021 |
| Auto collision repair noise measurements above the ACGIH limit | 4 of 18 | Bejan et al., JOEH 2011 |
| Peak sound pressure range at impulsive U.S. manufacturing sites | 108.8 to 134.4 dB | Erdreich, JASA 1986 |
| OSHA peak ceiling for impact noise | 140 dB | OSHA 29 CFR 1910.95 |
| EU peak action values | 135 and 137 dB(C) | EU Directive 2003/10/EC |
| U.S. workers exposed to hazardous noise each year | About 27 million | NIOSH 2026 |
| Oil-pulse vs double-hammer wrench noise | 8 dB(A) lower | Jeung and Kim, JKSOEH 1995 |
| Tyre shop workers with neurological vibration symptoms | 37.0% | Qamruddin et al., JOH 2019 |
Methodology and Sources
- U.S. Bureau of Labor Statistics, Survey of Occupational Injuries and Illnesses, Table SNR08: Incidence rates of nonfatal occupational illness by industry and category of illness, 2024
- California Department of Industrial Relations, Occupational Injuries and Illnesses Table 8, 2024
- Abdul Rahim et al., Identification of Noise Levels for Skill Training Activities, Equipment, Machines and Power Tools at TVET Institutes in Malaysia, IJERPH 2022
- Atlas Copco, W2410 impact wrench safety and product information (printed matter 9834 4674 00)
- OSHA Technical Manual, Section III Chapter 5: Noise
- Shi et al., Assessment of Occupational Hearing Loss Associated With Non-Gaussian Noise Using the Kurtosis-Adjusted Cumulative Noise Exposure Metric, Frontiers in Psychology 2022
- Zhang et al., The Role of the Kurtosis Metric in Evaluating the Risk of Occupational Hearing Loss Associated with Complex Noise, Zhejiang Province, 2010 to 2019, China CDC Weekly 2021
- Wang et al., Epidemiological characteristics of noise-induced hearing loss among workers in five automobile manufacturing enterprises in Zhejiang Province, Journal of Environmental and Occupational Medicine 2022
- Li et al., Threshold of kurtosis on occupational hearing loss associated with non-steady noise, Journal of Environmental and Occupational Medicine 2025
- Liu et al., Roles of A- and C-weighted kurtosis adjustment for equivalent sound level in evaluating occupational hearing loss, Journal of Environmental and Occupational Medicine 2025
- Erdreich, A distribution based definition of impulse noise, Journal of the Acoustical Society of America 1986 (NIOSH collection)
- Willson-Kerns and Brazile, Noise Exposure and Evaluation at Tire-Changing Facilities, Annals of Work Exposures and Health 2021
- Bejan, Brosseau and Parker, Exposure assessment in auto collision repair shops, Journal of Occupational and Environmental Hygiene 2011
- OSHA, 29 CFR 1910.95 Occupational Noise Exposure
- European Union, Directive 2003/10/EC on noise at work
- NIOSH, About Noise and Hearing Loss Prevention, updated 2026
- Jeung and Kim, Hand-Arm Vibration and Noise Levels of Double-Hammer Type and Oil-Pulse Type Impact Wrenches in Automobile Assembly Lines, Journal of Korean Society of Occupational and Environmental Hygiene 1995
- Markesino, Pruse and Rao, Study of Noise Transmission from an Electric Impact Wrench, NOISE-CON 2004 (NIOSH collection)
- Qamruddin et al., Prevalence of hand-arm vibration syndrome among tyre shop workers in Kelantan, Malaysia, Journal of Occupational Health 2019
- Data watch: BLS hearing loss rates count recorded illness cases by industry and cannot be attributed to impact wrenches specifically; stamping, presses and conveyors contribute in the same plants. National (BLS) and California (DIR) rates for transportation equipment manufacturing differ widely (9.8 vs 2.2 per 10,000), and the tables give no reason. The China CDC Weekly 2021 paper reports two different average prevalence figures for steady-noise workers (27.4% in its table and 15.04% in a figure), so we quote only its automobile row. The 2021 tire-shop paper cites the 2011 collision-shop study as 4 of 17 samples above the ACGIH limit, while the 2011 abstract itself says 4 of 18 measurements; we use the original. Manufacturer declared noise values (Atlas Copco) are lab figures the maker itself says are not adequate for risk assessment. No public quantitative dataset from the UAW Health and Safety Department or SAE on assembly-line wrench noise could be verified for this roundup. Several key studies are older than three years and are flagged in their sections (JASA 1986, JKSOEH 1995, NOISE-CON 2004, JOEH 2011); the Chinese kurtosis literature is the most active source of new data.
Last updated: October 18, 2026. We update this roundup quarterly, and the next refresh is expected when the Bureau of Labor Statistics publishes its 2025 Survey of Occupational Injuries and Illnesses illness tables.