Academic journal article Iranian Journal of Public Health

Noise Induced Hearing Loss in Iran: (1997-2012):: Systematic Review Article

Academic journal article Iranian Journal of Public Health

Noise Induced Hearing Loss in Iran: (1997-2012):: Systematic Review Article

Article excerpt

Introduction

Noise is a common harmful agent in workplace (1-5). Nearly 600 million workers around the world and millions of workers in Iran are constantly exposed to occupational noise (5-7). This occupational hazardous factor has adverse effects on the functioning of various body parts such as the auditory (1-7), circulation (2), Cardiovascular (5), neuropsychiatrie systems and productivity (7). According to WHO statistics, noise-related damages are estimated to reach 4 million dollars per day (7-8).

Auditory system is one of the main components of the communication (4). Auditory system impairment has always been one of the major concerns of occupational medicine and occupational health specialists. Though preventable, Noise-induced hearing loss (NIHL) is a debilitating and irreversible disease, which is one of the 10 leading occupational diseases (1, 4-7). This disease normally occurs 10-15 years after exposure to noise and starts mainly in 4000Hz frequency (4, 7). Noise-induced hearing loss starts classically in 3, 4 and 6 kHz frequencies, and extends to the lower frequencies in the chronic exposures (7, 9, 10).

During the recent 30-year period (1980-2012), several researchers have studied the association of noise, auditory system damage and other effects of noise in Iran's industries (1-2, 5-7, 11-30). This stream of research has investigated various Iranian occupational societies including oil, petrochemical, manufacturing, agriculture, textile, printing, stone production among others (1-2, 5-7, 11-30). Golmohammadi et al. (6) indicated that workers who were exposed to the noise 91.1 ±5.5 dB (A) that overall hearing loss determined 26.28±6.98 dB (A). They also found that the highest amount of hearing loss occurred in 4000 Hz. Bary et al. (12) showed that exposure to the noise level of 87.16 dB(A) induces to 4000 Hz and above hearing loss. Aghilinejad et al. (22) and Neghab et al. (2) showed that exposure to noise above 85 dB, leads to hearing loss and hypertension. Zare et al. (5) suggested that, at all frequencies (except 250 Hz), the hearing thresholds of individuals exposed to upper 85 dB(A) noise, was significantly hearing loss higher than that of the control group at all frequencies (except 250 Hz). Furthermore, Attarchi et al. (1) indicated that the Hearing loss in workers exposed to above 90 dB (A) noise was significantly higher than that in workers who are exposed to lower levels of noise.

"Noise Exposure limits" is one of the important issues in the assessment of relationship between noise exposure and hearing loss. Among existing standards, OSHA uses 90 dB(A) standards with 5 dB(A) rule, ISO and Euro countries use 90 dB(A) standard with 3 dB(A) rule, and ACGIH and NIOSH use 85 dB(A) standard with 3 dB(A) rule. The second version Occupational Exposure Limits (OEL) in Iran is similar to ACGIH Threshold Limit Values (TLVs) (4).

Laboratory and epidemiological studies are basics in occupational exposure limits, in order to develop the third Iranian occupational exposure limit (OEL), we decided to review various studies conducted over the past 15 years in Iran. Then, the purpose of present study was a systematic review of relevant literatures related to the noiseinduced hearing loss, lead to developing noise exposure limits.

Methods

Article search

In November 2012, through a systematic review we searched for all published papers in this field, looking into such databases as ISI Web of Knowledge, Scopus, PubMed, SID, ISC, ScinceDirect and Iran Medex. Key words used included noise plus hearing loss; noise induced hearing loss, NIHL, and hearing threshold shift. In addition, the websites of occupational health related journals (including Iran occupational health, health and environment, JHOE journals and scientific medical journals) were explored. Furthermore, the libraries of major Iranian universities of medical sciences (Including Tehran, Shahid Beheshti, Hamadan, Esfahan and Shiraz) were investigated and relevant thesis and research reports were reviewed. …

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