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Setting the Noise Agenda

Published: 01st Sep 2012 in OSA Magazine

The problem in context

Asia comprises 47 countries. It is the world’s largest and most populous continent. Its population is estimated at four billion people, representing 60 percent of the world’s current human population (Population Reference Bureau, 2010).

It is rich in natural resources such as petroleum, forests, fish, copper and silver. The current trend in many developing Asian countries is that workers are moving from agriculture to the manufacturing industry sector. Millions of workers are employed in manufacturing companies, especially in mainland China, South Korea, Taiwan, Thailand and Vietnam. Indeed, for most of the Asia Pacific countries the rapidity of industrialisation largely accounted for the economic growth of these nations in the late 1980s (Wilkinson, 1994).

In China alone, from 1979 to 1991, the number of industrial enterprises increased by a factor of 12 and the number of employees has multiplied by 2.4 times (Zhi et al, 2000). Many companies from developed countries have moved their manufacturing plants to these countries due to cheaper labour, yet with good access to technology. In countries such as Indonesia and Malaysia the foreign direct investment (FDI) in the manufacturing industry represents approximately 70 percent and 83 percent of the total FDI, respectively (Daquila, 2004).
In the footwear industry alone, of the ten countries that were identified as the leading producers of footwear in 1998, mainland China accounted for almost 50 percent of world production (SATRA, 2000). This trend has created occupational health and safety (OHS) issues such as more sources of noise emissions, smaller ratio of OHS-related professionals per number of workers, the use of other hazardous agents such as ototoxic chemicals along with an increased increment in the number of labourers at risk of developing noise induced hearing loss.

In developed countries as opposed to developing ones, noise emissions from machinery are periodically measured and actions to reduce hazardous noise exposures are taken. In developing Asian countries due to the lack of specific legislation regarding noise emissions, or simply due to the lack of personnel from local governments to inspect factories, noise emissions are rarely controlled.

The International Labour Organisation (ILO, 2006) has suggested that countries should have at least one inspector for every 10,000 workers, whereas in Asian countries such as mainland China there is one inspector for every 35,000 workers (O’Rouke & Brown, 2003). Thus, high environmental noise levels are part of the daily lives of most Asian labourers.

Agriculture still remains as one the main industries of countries such as India, Pakistan and Bangladesh. In India, 60 percent of labourers still work in the agricultural sector (Sundaram, 2001). Farmers are also at risk of NIHL as tractors, sugarcane crushers, and other machines are noisy tools used daily on contemporary Asian farms. Tractor designs in high income countries have become more sophisticated and most of them have enclosed environment controlled suspended cabins. These designs are not likely to become common in countries like India in the near future (Kumar et al, 2005).

Currently, tractors in India and other developing Asian countries do not have adequate vibration and sound attenuating design features. A fact to be taken into consideration is that, in India alone, the use of tractors has increased from 52,000 in the 1960s to 3.2 million in the 1990s (Motor Transport of India, 2003). Similarly, in Pakistan, the number of tractors has increased from 35,700 (1974) to 401,700 (2004), (Government of Pakistan Statistics Division Agricultural Census Organisation, 2004).

Other important industries in the region which represent a risk for workers’ hearing health are commercial fishing and mining. Fishing is the largest industry in the Maldives, contributing 68 percent of the export earning and employing more than 10 percent of the total working population in this country (Chowdhury, 2008). The mining sector is Mongolia’s single largest industry, accounting for 55 percent of industrial output and more than 40 percent of export earnings (Mongolian National Statistical Office, 2002). Thus, Asian workers in manufacturing, agricultural, fishing and mining industries are at high risk of acquiring NIHL. This scenario becomes worse as a high percentage of workers in developing Asian countries are part of the informal sector.

Sources of noise and prevalence of NIHL

From the OHS point of view, the sources of noise are directly related to the main industries of a region or country. As discussed above, different economic sectors contribute to NIHL in Asia. The manufacturing industry, however, has been the most commonly investigated in studies on environmental noise levels and prevalence of NIHL in Asian countries. Table 1 summarises different studies on noise levels and NIHL prevalence for different countries and industries in Asia.

It is important to mention that in the studies summarised in Table 1 and discussed below, the methodology utilised regarding noise measurements differed markedly. Some studies reported noise levels in dBA, measured only once at a specific time, and others reported the time-weighted average of noise exposure for eight hours a day/five days a week in dBA Leq. Also, a high prevalence of NIHL has been consistently reported among these workers. The reader should be aware that the definition of NIHL varies among studies. Some studies have considered NIHL as the average of high frequency thresholds, others as the average of speech frequencies, and others simply as an audiometric notch configuration at a high frequency.

A study conducted in Taiwan (Wu et al, 1998) investigated nearly 10,000 workers exposed to noise levels above 85 dBA from different sectors. They found that 34 percent of workers had hearing thresholds at 4 kHz higher than 40 dB in either one or both ears. Among the workers presenting with hearing loss at 4 kHz, 58 percent had hearing thresholds between 40 and 55 dB, and 42 percent had hearing thresholds at 4 kHz above 55 dB in either one or both ears.

The more severe cases of hearing loss were found in workers from construction, weapon manufacturing, and ship building/repairing industries. Indeed, in these industries, noise levels were higher than in other industries investigated by the authors such as food processing, transportation, and oil refining, among others. The same study found that workers in the transportation industry (e.g. bus drivers, truck drivers, and airline pilots) had relatively good hearing ability and showed a low prevalence of severe NIHL (hearing thresholds at 4 kHz above 55 dB HL). Another study in Taiwan found a 57 percent prevalence of NIHL, defined as hearing levels above 25 dB HL for the average of 500, 1,000, and 2,000 Hz, among workers exposed to a mean equivalent sound level (Leq) of 79 dBA (Chang & Chang, 2009).

In Japan, Miyakita and Ueda (1997) based on the data of the survey on the periodical medical examination (Ministry of Labour, 1993) calculated the number of workers in the country’s major industries with a notch (>40 dB HL) at 4 and 1 kHz. From the total number of workers (7,975,175) examined in the 1993 survey, ten percent presented with a notch at 4 kHz, and five percent with a notch at 1 kHz (Miyakita & Ueda, 1997). The authors reported that agriculture, forestry, fishing, mining, construction and manufacturing were the industries where more than ten percent of workers had a notch at 4 kHz. It is important to mention that In Japan, enterprises with more than 50 workers must report the results from medical examinations. Industries with more than 50 workers, however, represent only 35 percent of the workforce in Japan.

In Mainland China, a local study (Zhi et al, 2000) has estimated a 34 percent prevalence of hearing loss in workers from rural industrial enterprises or township factories relating to textile, production of construction materials, and electrical machinery manufacture. The authors investigated a total of 5,197 worksites in different enterprises. Forty-three percent of the worksites had noise levels above 90 dBA, and those above 95 dBA were 23 percent of the total sample investigated.

Zhi et al (2000) claimed that most township enterprises do not provide basic occupational health services. Also in Mainland China, Ni et al (2007) studied 618 female workers from a textile mill. A total of eight workshops were investigated. Five different sites were monitored for each workshop. Noise levels at each site were sampled three times per minute. Also, time-weighted averages (TWA) were calculated. Noise levels from the single measurements varied from 80.1 to 113.8 dBA. Cumulative noise exposure varied from 84 to 103 Leq (dBA), considering eight hour work shifts. Workers from weaving workstations were the ones with the highest noise exposure, which varied between 102.3 Leq (dBA) to 103 Leq (dBA). A total of 24 percent of the workers presented with high frequency hearing loss. The authors mentioned that all of the workers were provided with earplugs but only 25 percent of the workers wore them.

In India, Patwardhan et al (1991) studied the noise levels which drivers from State Transport Sangli depot were exposed to, and also they investigated the hearing thresholds of these drivers. Single noise levels in the driver’s cabin were obtained. These measurements were carried out in seven different buses. The results showed noise levels between 89 to 106 dBA.

Audiometric tests were carried out in 200 drivers from whom 75 percent presented with sensorineural hearing loss (SNHL). Also in India, Kumar et al (2005) studied the noise levels emitted by tractors and other machinery relating to agriculture, as well as the hearing levels of agricultural workers who did (tractor drivers; study group) and did not drive tractors (non tractor drivers; control group). Results showed that tractors emitted noise levels above 110 dBA, and noise levels from other machinery utilised by both tractor and non tractor drivers such as diesel pump sets, fodder cutter machines and sugar cane crushers exceeded 90 dBA.

Hearing loss was determined as either high frequency hearing loss (HFHL) (25 dB HL or above of the average of 3,000, 4,000, 6,000, and 8,000 Hz) or mid-frequency hearing loss (MFHL) (25 dB HL or above of the average of 500, 1000, 2000, and 3000 Hz). Results from the hearing tests showed that 48 percent of tractor drivers presented with HFHL in comparison to 28 percent of non tractor drivers, and 26 percent of tractor drivers presented with MFHL in comparison to 20 percent of non tractor drivers.

In Pakistan, Siddiqui and Siddiqui (2008) investigated the prevalence of hearing loss among aviation male workers at Karachi airport compared to an age-matched control group of male workers who perform their duties elsewhere. Noise levels were randomly obtained three times on the same visit at the workplace (runway) and at the residence of the airport workers (adjacent to the runway). Similarly, noise levels were randomly measured three times at the workplace of the control group workers.

The mean noise level obtained from the aforementioned measurements was 110 dBA for airport workers’ workplace, and 69 dBA for the non airport workers’ workplace. The degree of hearing loss for each single worker was classified according to the World Health Organization (WHO) guidelines (WHO, 1991). Degrees of hearing loss for low frequencies (500, 1000, and 2000 Hz), and high frequencies (3,000, 4,000, and 6,000 Hz) were calculated for both study and control groups. Mild to severe hearing loss for the low frequencies was observed in 66.1 percent of airport workers in comparison to 14.5 percent of non airport workers. Mild to severe hearing loss for the high frequencies was observed in 86.4 percent of airport workers in comparison to 5.7 percent of non airport workers.

The authors asserted that aggressive hearing conservation measures are required for these aviation workers. Also in Pakistan, Ashraf et al (2009) studied the prevalence of hearing loss among textile industry workers in the weaving departments of five textile factories. Single noise level measurements were carried out at different locations in the areas of the weaving sections of the factories. Noise levels obtained varied between 88 to 104 dBA. Almost all of the workers (93 percent) were aware that high noise levels cause speech interference, but 57 percent were unaware of the deleterious effect of noise on hearing health. About half (55 percent) utilised hearing protection. Hearing loss was found in 17 percent of workers. The authors claimed that the development and implementation of noise regulations in Pakistan is immediately needed.

Noise sources, however, are not limited to the manufacturing industry or aviation in Asian countries. Reports of high noise levels in urban areas and the prevalence of NIHL in those who work in the informal sector (e.g. hawkers) have been published. In Dhaka (Bangladesh) Chakraborty et al (2005) carried out a study investigating average noise levels at different places of Dhaka Metropolitan City (DMC) and its impact on residents’ hearing levels. The highest noise level recorded was 104 dBA at a bus terminal and the lowest 68 dBA in a residential area. A notch (>25 dB HL) at 4 kHz was observed in ten percent of the audiograms of the study population.

Automobile drivers, traffic police, road side-hawkers, shop keepers, and garment workers were mostly affected. The majority (78 percent) of the research participants had a poor level of knowledge regarding the deleterious effects of noise on health and about the hearing protection available.

Similarly in Nepal, studies investigating noise levels in different parts of the city of Kathmandu have been conducted (Joshi et al, 2003). Noise levels between 70 to 100 dBA were recorded in urban roads in Kathmandu. Vehicle engines, loud and prolonged car horns, road-tyre friction, gear box and exhaust system were identified as the major sources of noise pollution (Joshi et al, 2003).

In Pakistan, Merchant et al (2000) investigated self-reported hearing difficulties due to noise exposure among rickshaw drivers and taxi drivers in Karachi. Rickshaw drivers were about thrice as likely as taxi drivers to report significant hearing difficulties, twice as likely to report tinnitus and two and a half times as likely to have difficulty in following telephone conversations. Similarly, Aslam et al (2008) found a 65 percent prevalence of hearing loss among public transport drivers in the city of Lahore in Pakistan.

In Malaysia, Thomas et al (2007) measured noise levels in 32 different places in Kuala Lumpur. Sound level readings were obtained three times during one day. Results showed that noise levels on average varied between 75 and 85 dBA. The highest level obtained was 108.2 dBA at one place only. Pure-tone audiometry was carried out in a sample of 30 traffic point duty personnel. NIHL characterised by a notch at 4 kHz was found in 70 percent of the sample studied. According to the results of a questionnaire given to the research participants, nearly 80 percent did not know about occupational safety and personal protective equipment.

In summary, different studies have demonstrated that a high number of Asian labourers are exposed to noise levels above 85 dBA. In the studies discussed above, different industries have been investigated with textile, oil refinery, agriculture, aviation, and transport being the most common ones. In mainland China, textile industries were suggested as the ones with the highest number of workers exposed to hazards including noise (Zhi et al, 2000).

Final remarks

NIHL in Asia represents a complex scenario where multiple factors interact. Despite the existence of legislation in most Asian countries, this legislation is not adequately enforced. Legislation on the implementation of hearing conservation programmes (HCPs) exists in some Asian countries; however, in others is negligible.

These issues together with the lack of awareness on NIHL among workers, employers and even HCPs lead to the high prevalence of NIHL observed in Asian labourers. Another issue is the lack of local research on NIHL being conducted in Asian countries. Although there are some studies of noise sources and prevalence of NIHL for different industrial sectors, there is still a need for more local studies.

No peer-reviewed studies are available for many large countries, such as Myanmar, Malaysia, Vietnam, Indonesia, and others. Research on the implementation of HCPs is almost absent in Asian countries and there is therefore a pressing need for research in this area.

Awareness of the deleterious effects of noise should be disseminated among employers and employees and, indeed, health professionals should take a more active role in this endeavour.

NIHL continues to be the most prevalent preventable occupational disease in many Asian countries. It is the role of local governments and health care professionals to reduce the prevalence of NIHL and thus protect hearing health, with the ultimate goal of enhancing the quality of life of millions of Asian people. 

Published: 01st Sep 2012 in OSA Magazine


Dr Adrian Fuente

School of Health and Rehabilitation Sciences, University of Queensland Brisbane, Australia Adrian Fuente is a NHMRC Senior Research Officer at the School of Health and Rehabilitation Sciences, University of Queensland (Brisbane, Australia). Adrian obtained his Bachelor degree in Speech Pathology and Audiology from the University of Chile in 2000. In 2003 he moved to Hong Kong to study his PhD in Audiology which was completed in 2008. In 2009, he joined the Audiology Department at the University of Queensland as a Postdoctoral Research Fellow. His research interests include noise-induced hearing loss and the deleterious effect of chemical exposure on the auditory system, specifically on the central auditory nervous system. Adrian has published several research papers in these fields and has been an invited speaker in a number of international conferences.

Dr Adrian Fuente




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