Figure 1 Distribution of the NIHL in High frequencies (n1=113) by age groups and duration of exposure to noise.

In this study: We found that only 34worker were from rural area while 150worker were from urban areas, while (n1=113) distribution appear to be 8 and 105worker among the rural and urban workers respectively as shown in Table 4.

The chief complaint regarding their ears had been survey also as shown its distribution in Table 5 and Figure 2 which demonstrate 54, 80, 108 and 55worker complained from hearing difficulty, tinnitus, Ear discomfort and Vertigo/dizziness respectively.

Figure 2 Distribution of workers depending on their chief complaint.

The questioner also gave results about the No. of workers who have Vitamin uses, Special Diet  uses (Garlic as example of Antioxidant food staff), uses of personal noise protective devices (PPD), Did not consider the noise as a hazard on health ,all results are seen in Table 6. Which demonstrate that? The smoking habit (mild, moderate or heavy) distribution among the workers and the influence of the smoking on the incident of Noise Induced Hearing Loss can be shown in Table 7. The questioner paper contained many other items which were asked to the employees, and the most remarkable thing which this study considered it as one of the aims are the Associated chronic illness( HT, IHD, RF) as shown in Table 8. The questionnaire which done by the trained medical staff also got the distribution of the workers depending on their education level which shows 64, 100 and 16 workers distributed among primary, secondary and University Education level as can be detected in Table 9.

At the 12 measurement point sites, in knitting section, the mean level of noise was 87-96dBspl. Which is more than the allowable level of noise for continuous  8hours working/day depending on the OSHA (Occupational Safety and Health Administration)¹³ which seen as below; although a limited number of weaving machines are still working till now (about 50% of all machine is working) those because many of them stop their working due to decrease in products orders to the factory in last year’s, the condition which may share in prevent increasing of accumulative noise of considerable number engines when working simultaneously.

Safe Sound Level:  The guidelines of The National Institute for Occupational Safety and Health (NIOSH) are declared that the upper time limit that you can be safely exposure  to many Time Weighted Averages (TWAs) of level sound pressure on a daily basis over a 40years period.

T.W.A. Decibel Levels          Maximum Exposure

85dB                                    8hours

88dB                                    4hours

91dB                                    2hours

94dB                                    1hour

97dB                                    30minutes

100dB                                  15minutes

103dB                                   7½minutes

106dB                                    3¾minutes

Exposure to 115+dB or greater may pose a serious health risk.¹⁴ In this study, it was found that weavers in the knitting factory observed were insecure to dangerous noise levels, which are mean above 90dBA, the threshold limit value set and this was the first noise and loss of hearing survey. The assessment Audiometric showed that 113 worker (left ear) had loss of hearing in the high frequency while only 54 worker complained from hearing difficulty, because Noise Induced Hearing Loss usually include at first the high frequencies (which is commonly away from the speech frequencies), therefore the worker can develop the Noise Induced Loss of hearing and he didn’t complain from loss of hearing, the workers may complain only ear discomfort or tinnitus which could be the only presenting symptoms as they were in our study 80 and 102 respectively. The hearing loss classify according to WHO (International Classification of Impairment, Disabilities and Handicaps).¹⁵ As below: 

Hearing Loss (dB)                           Degree of Hearing Loss                                            

>26                                                   Normal Hearing

26-40                                                Mild

41-55                                                Moderate

56-70                                                moderately severe

71-90                                                Severe

>90                                                   Profound

And in our study we found the greatest percentage of loss of hearing was in the mild/ high frequency group and the minimal Noise Induced Hearing Loss notch at 2kHz and 4KHz were 6% and 22% of workers respectively in our study, even though some of them hadn’t symptoms.

According to¹⁶ show that the Noise Induced Hearing Loss ratio was remarkably more common on the exposed workers and it is not possible to found any clear cut difference between unsafe and safe exposure to noise. In general, restrict a reset with increase of the protecting to 90% or more of an exposed population.¹⁶ David M Barrs et al they found that the minimum Noise Induced Hearing Loss notch at 3-6kHz in about 1/3rd of the workers (37%) in their study they hadn’t symptoms.¹⁷ It is reasonable now that the risk damage of  hearing is negligible at noise levels of less than 75dB(A) for 8hours daily  continuous exposure and even exposure at levels up to 80dB(A) there was no obvious increase in the percentage of workers with loss of hearing¹⁸ there was difference between worker  in units level below 80dB(A) and the other groups of workers exposed to (80-85dB(A), above 85dB(A). it was shown that Noise Induced Hearing Loss prevalence on subjects exposed to noise level below 80dB(A) was not insignificant (grade 3:32.43% and grade 4-5:10.18%)(15). Non-existence of noise-reduction measures and no using of the protective devices, might explain the high spread of the Noise Induced Hearing Loss in Meliksah et al study.¹⁶

In our study we show that there was a strong association between  Age of worker/the duration of exposure  to the noise of employment and hearing level, when it was 89% and 100% for the late two age groups the( 46_50 year) and  (≥50) giving the p-value≤0.05 and≤0.001  respectively. According to Barrs MB¹⁹ the influence of age has another effect on the primary noise induced hearing loss.¹⁷ Always these investigations it was established that the duration of occupation was the most definitive cause for obvious increase hearing loss.¹⁹ In order to show the influence of noisy environment, age factor must be regulated. Ivarsson A et al.²⁰ show that age can only regard as insignificant amount of variability across the subjects in their tendency to Noise Induced Hearing Loss.²⁰ U.G.Olero et al declare that hearing threshold for the exposed workers increased with both age and duration of occupation and were significantly corresponding to (r=0.26, p≤ 0.05) with duration of occupation. ²¹ Gunter Rosler found that combination of eleven investigations by many authors regarding the advancement of hearing retro gradation during severe long-term exposure to noise.

Günter Rösler found a weak correlation between duration of employment and hearing level. This might be explained by the long duration of employment. While according to¹⁶ the majority of the workers’ occupation durations were>ten years. It should be significant to comparison between the first attending hearing levels with today hearing levels but we had no data about the levels of hearing of the workers’ before they had presented to the factory many years ago. In our study we found that 69 workers were smokers distributed among mild, moderate and heavy smoking types making a 38% of the smoker worker out of 184 workers (p-value≤0.05) which might indicate a strong relation also between smoking and the enhancement of NIHL occurrence. According to Cruickshanks KJ et al it: the smoking increased the chance of loss hearing about doubled, as seen similarly in many smaller groups of studies^22–24

Cruickshanks KJ found that diabetes increased the chance of loss hearing by double fold, giving more information about the effect of diabetes on the loss of hearing.^{25– 27} Cruickshanks KJ study also prove that a significant relation between noise exposure particularly firearm exposure to noise and hearing loss. ^{28– 31} The effects of these specific frequency exposures further refines their knowledge of these relations.³² Diabetes and smoking were significantly related with loss of hearing across the frequency spectrum (affecting the cochlea in the inner ear from the apex to the base). In contrast, only in high frequencies noise exposure was significantly associated with loss of hearing.^33–35 

In our study 30 workers they had an associated chronic illness (DM or IHD), only 11 (37%) workers out of them showed NIHL ((p-value≤0.05) which might indicate a strong relation between diabetes/or Ischemic heart disease and the enhancement of NIHL occurrence. In our study no one of the survived workers used the personal noise protective devices (PPD) and only 44 workers (24%) (p-value≤ 0.1)   who considers the noise as a hazard on health, and this represent a small group who can be regarded as a well cultured people against pollution and NIHL. Moreover there was no distinction or impaction of the level of learning upon the use of special noise protective devices (PPD) where Table 9 Show us that we got adversity of level of learning among the workers. In spite of that it was not the case in (PPD) application study done by Pranee Chavalitsakulchai et al.³⁶ who found that usage of the personal noise protective devices (PPD) in 469 weaving workers were checked. 215 workers (45.8%) claimed that they often use (PPD), 73 workers (15.6%) sometimes use (PPD), and 181 workers (38.6%) never use (PPD (.

There was no variation in average length of appointments among these groups shows the reasons why 181 workers never use (PPD). Discomfort was the most common reason. The "never use" workers group had considerable loss hearing at 2000Hz, 4000Hz frequencies (P<0.01), 8000Hz resemble to the "often use" workers group. Compared with the "sometimes use" workers group, the level hearing of the "never use" group were considerably worse at the level of 2000Hz (P<0.01), 4000Hz (P<0.05), and at the level of 8000Hz (P<0.05). A surprising finding was that the workers whom using PPDs also establishing to have loss of hearing. Loss of hearing appeared even in the group of workers who used the personal noise protective devices (PPD). The same occurrence was described in a Singapore stud5). One probable cause is that the personal noise protective devices (PPD) manufactured in the developed countries might not be well probable to Thailand workers. Another reason is that many workers use only plugs of cotton as (PPD) and they are not effective.^36–38 However in the Swedish industries it was clarified that, the more commonly use of the protectors of hearing and noise-reduction measures had reduced hearing damage to teeny workers.^39–42 

Regarding the utilize of special food staff, in this study it has been found that  40workers out of 184workers examined usually use garlic regularly within their food items, however 10worker ( 25.5%) who had NIHL were also use garlic regularly(P<0.5 ) which shows a week correlation. Clifford RE et al.⁴³ demonstrate that protective effects of antioxidant medicines on animal studies showed opposite to Noise Induced Hearing Loss and it is unclear whether antioxidants would protect humans from NIHL.⁴³ also performed a study to decide whether N-Acetyl-cysteine (NAC) preserve workers versus noise induced temporary threshold shift (TTS).⁴³ Considered that after continuous noise  exposure to only DMET or both of low-dose DMET/NAC  a significant recovery of hearing was noticed, demonstrating a lot of small dose of antioxidants required than previously reported for hearing recovery following acoustic trauma.⁴⁴ While showed The administration of the antioxidants to animals in which free essential forming had already been reduced by previous injection of furosemide didn’t have an extra preventative action on the NIHL.⁴⁵