Noise is ubiquitous in industry. Continuous exposure to noise levels above 90 dBA can produce adverse auditory and non-auditory health effects. Studies carried out by NIOH showed that the sound pressure levels were very high in various industries, ranging from 102-114 dBA in textile industries, 93-103 dBA in pharmaceutical firms, 90-102 dBA in fertilizer plants, 90-119 dBA in oil and natural gas complexes in Bombay High, 60-102 dBA due to road traffic in Ahmedabad city, 90-102 dBA in surface rail traffic, 70-111 dBA in metro rail, 90-112 dBA for air traffic. The following health effects were observed due to excessive noise.
Hearing acuity of textile weavers aged 25-39 years, exposed to a noise level of 102-104 dBA was found to be poor. Noise induced hearing loss (NIHL) at 4000Hz was as high as 30 dB in the age range 25-29 yrs, 40 dB in the age range 30-34 yrs and 45 dB in the age range 35-39. The NIHL at 4000Hz is known to be irreversible.
In addition to hearing loss, exposure of workers to noise levels of 90-119 dBA was also found to result in sleep disorders, mental fatigue, annoyance and reduced alertness compared to those working in a relatively quiet room (60-75 dBA). Further, it was seen that the speed of performance was impaired significantly by noise. Adverse effects of noise were observed in tweezer dexterity with higher degree of degradation observed at moderately different levels of the task. Similar observation was also noticeable in two hand coordination. Reaction time was enhanced under high noise condition. Certain physiological measures (oral temperature, pulse rate and skin temperature) were also found to be high in workers engaged at high noise condition.
The production data of each weaver collected for at least 15 days after the weavers were found to have had worn hearing protection devices (ear plug and ear muff) for 30 successive days was examined. The results showed that the production of the weavers wearing ear-muffs aided with ear plugs was significantly higher than the other weavers. The findings thus suggest that the weavers with hearing protection devices had an increased rate of production, parallel to the increasing degree of protection from noise rendered by the protective devices.
Interaction Effects of Noise and Heat
The interaction effects of noise and heat on neuromotor based functions were studied in acoustic chamber. The combined effect of heat (35°C) and noise (100 dB) caused higher error rate in card sorting (face value) and decreased accuracy in reasoning ability.
Noise and Illumination
The interaction effect of noise and illumination on performance efficiency examined under six experimental conditions of three levels of illumination (50, 150 and 300 Lux) and two levels of noise (70 and 100 dB) revealed significant slowing of response rate in letter cancellation test in noise condition of 100 dB and progressive improvement with the gradual rise of illumination level. The combined effect of noise and illumination on the accuracy scores reflected performance decrement under high illumination level (300 Lux) and under high noise condition (100 dB). The rate of decline in the accuracy and efficiency of performance in hand precision test under high illumination level was significantly more pronounced under noise condition than in the quiet condition (70 dB).