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Occupational Noise-Induced Hearing Loss Review Occupational Noise-induced Hearing Loss MH Azizi Abstract Academy of Medical Noise-induced hearing loss (NIHL) is a well-known entity in daily practice of otolaryngol- Sciences of the IR Iran, ogy. A wide variety of NIHLs are work-related. Occupational noise is the most common cause Tehran, Iran of NIHL in adults which is up to now considered incurable and the best approach to it is to utilize maximal protection. An effective noise exposure prevention program consists of iden- WL¿FDWLRQRIVRXUFHVRIQRLVHDQGLPSOHPHQWDWLRQRIFRQWUROOLQJPHDVXUHVDQGUHJXODWLRQVDW working environments as well as performing periodic audiologic evaluation of those who are ZRUNLQJDWQRLV\HQYLURQPHQWV7KHSUHVHQWSDSHUEULHÀ\UHYLHZVRFFXSDWLRQDO1,+/PDLQO\ based on the related data available on PubMed up to early 2010. Keywords: Noise; Hearing Loss, Noise-Induced; Occupational Diseases Introduction gram and in due course in 1939, Bunch oise is considered as an “unwant- explained broadly the audiometric find- ed sound”1 with various harmful ings of NIHL.2 effects on health. Noise-induced At global scale, the major cause of NIHL N 3 hearing loss (NIHL) is an irreversible in adults is occupational noise which damage of the cochlear hair cells of the in- seems to be currently increasing in devel- ner ear. It may present as partial or total oping countries. hearing loss and its severity depends pri- Occupations at risk marily on duration of noise exposure and sound intensity. Noise production has raised parallel with The history of occupational NIHL the industrial growth and technologic ad- (ONIHL) probably dates back to many vancements and presently, many people centuries ago, even though as Alberti stat- in the world are exposed to intermittent or ed, it only became a major occupational continuous hazardous sound levels (>85 aural disorder after discovery of gunpow- dB) at their work environments. der and has increased significantly after Many workers including those engaged the Industrial Revolution. From audio- in heavy industry, factories, forge ham- logical point of view, for the first time in mering, coal and ore mining, construction, 1886, Thomas Barr described the “boiler- cement plants, gas processing industry Correspondence to maker’s deafness” related to shipbuilding. and mechanical engineering as well as Mohammad-Hossein Then, the histological features of NIHL in mill and stationary machine device opera- Azizi, MD, Otolaryn- gologist, the organ of Corti of the inner ear were tors and workers at oil refineries are at risk Academy of Medical Sciences of the IR Iran, demonstrated by Haberman in 1890. Af- of occupational NIHL. For instance, in a Tehran, Iran. terwards, Fowler described the character- metalworking company in Brazil, the rate Tel: +98-212-293-9869, E-mail: [email protected] istic noise-induced 4 kHz notch on audio- of suggestive cases of NIHL was around 116 www.theijoem.com Vol 1 Number 3; July, 2010 rev i ew M. H. Azizi 15.9%.4 In a similar survey studying NIHL One study showed that 36% of firefight- among the US mine workers, the investi- ers had a moderate to severe SNHL at 3, 4, gators found that certain pieces of equip- or 6 kHz.13 They were exposed to a harm- ment in coal primary plants were the ful level of intermittent noise from sirens, loudest sources of noise production.5 In air horns, engines of emergency vehicles another investigation performed in Iran, and fire trucks.14 the audiometric assessment of the work- Railroad service employees including ers in a textile plant who were occupied locomotive crew are also exposed to noise in spinning and weaving units confirmed and at potential risk of developing ONI- a significant increase in the prevalence of HL.15 high frequency sensorineural hearing loss Farmers may face occupational hearing (SNHL).6 In another study on 384 workers loss for exposure to noise produced by ag- at an oil refinery in Taiwan, the research- ricultural machineries. Concurrent expo- ers showed that those workers who had sure to chemicals including solvents and been exposed to noise for more than 15 pesticides may also potentiate their hear- years had an increased hearing threshold ing impairment.16 shifts at high frequencies (i.e., 3, 4, and 6 The drivers and operators of heavy kHz).7 trucks would be exposed to noise. In a re- Civilian aviation started in the first cent study from Iran, it was shown that in decades of the twentieth century.8 Flight professional drivers hearing impairment crews, pilots, airline ramp employees, and appeared earlier at 4 and 8 kHz than lower maintenance workers at airports are all frequencies.17 at potential risk of NIHL. In a study per- Hearing status of 200 traffic policemen formed on full-time male workers working in Moscow was compared to that of 50 po- at a large metropolitan airport in Korea, it licemen who had been working in offices. was shown that occupational noise expo- The results revealed a higher prevalence of sure, other risk factors (e.g., non-occupa- ONIHL in traffic policemen.18 tional noise exposure, history of pervious Among musicians, rock and roll devo- ear diseases, taking ototoxic drugs, smok- tees are especially at risk of developing ing and hypertension), and use of hearing ONIHL. Professional orchestral musicians protective devices were significantly asso- also run the risk of developing ONIHL.19 ciated with hearing status of these work- In a study, players of the principal trum- ers.9 In another study conducted in 2007, pet, first and third horns and principal out of 609 pilots aged between 26 and 68 trombone were at the greatest risk of ex- years, 431 (70.8%) had SNHL.10 posure to excessive continues noise, while Military personnel including pilots the percussion and timpani players were are exposed potentially to loud sounds. at the maximum exposure to excessive Acoustic trauma may occur during mili- peak noise levels.20 tary service due to impulse or blast wave In the past few decades, the occurrence noise exposure.11 The prevalence of hear- of ONIHL in dentists has been discussed ing loss in an army aircrew was reported in the literature. For instance, Bail and in 1996 by Owen. The study revealed that coworkers reported the shifts of hearing those aircrew with more than ten years of thresholds at 4 and 6 kHz in a group of flying experience had a hearing threshold dentists.21 Other studies also confirmed shift correlated with their age and number the problem of early hearing loss among of years of flying.12 dentists which is caused by high-speed air www.theijoem.com Vol 1 Number 3; July, 2010 117 rev i ew Noise-induced Hearing Loss Rose and colleagues confirmed the popular sport of stock car racing as a po- TAKE-HOME MESSAGE tentially significant source of noise expo- sure. They found that the peak sound level ● Noise-induced hearing loss is an irre- versible damage of the cochlear hair six meters away from the track was 109 dB, cells of the inner ear. which was higher than permissible sound level.27 ● Occupational noise is the most com- Another study showed that several or- mon cause of noise-induced hearing thopedic instruments produced sound lev- lossin adults. els between 95 and 106 dB with potential risk of developing NIHL.28 ● Tinnitus as an occupational noise- induced symptom should always be Symptoms considered in those with noise-in- duced hearing loss. Besides to SNHL which is caused by pro- longed noise exposure, the association of ● Exposure to noise of pregnant wom- NIHL and tinnitus is fully described in the en at working places may affect the literature and it has been shown that tin- hearing of their unborn children. nitus would be increased with progression of noise-induced auditory damage. The severity of tinnitus depends on age and 22 turbines. duration of noise exposure.29 In case of In a 12-year prospective study carried occupational noise exposure, many tinni- out on hearing thresholds of 477 profes- tus sufferers probably remain undetected. sional divers in Norway, the investigator Therefore, tinnitus as an occupational found a correlation between hearing im- noise-induced symptom should always be pairment and diving. In that study, hear- considered in those with NIHL.30 ing loss was noticed at frequencies of 4 and 8 kHz.23 Moreover, permanent bi- Risk Factors lateral SNHL has been demonstrated in professional scuba divers.24 Barotrauma, Rheumatoid arthritis and decompression sickness and noise are re- diabetes mellitus garded as the main causes of hearing loss Employees with rheumatoid arthritis among different diving groups.23 or diabetes mellitus who are working in The problem of noise exposure in em- noisy environments are at a higher risk of ployees of a hospital kitchen has been developing NIHL.31 reported in a study; the author recom- mended metal-to-metal contact must be Chemical substances reduced as much as possible and hearing Hazardous effect of noise on hearing may protectors should be provided to employ- be potentiated by concurrent exposure to ees working in the dishwashing room until ototoxic or non-ototoxic chemical sub- proper control is applied.25 stances. For instance, it has been shown The researchers in Denmark assessed that exposure to low to moderate levels the hearing loss among the seafarers and of carbon monoxide or hydrogen cyanide fishermen and reported that hearing loss can increase the likelihood of developing was a common problem among the work- NIHL.32 In another study, the role of ex- ers of the engine rooms of ships.26 posure to organophosphate pesticides as a 118 www.theijoem.com Vol 1 Number 3; July, 2010 rev i ew M. H. Azizi risk factor for developing hearing loss in tioning factory in southern China, 2400 those farmers who were simultaneously workers who were exposed to noise were exposed to noise has been discussed.33 evaluated.
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