Introduction. Noise is generally defined as unwanted, unpleasant or disturbing sound. The intensity or loudness of sound is measured in decibels (dB), on a logarithmic scale. Our ears can tolerate only a limited range of sound intensity. Prolonged exposure beyond a certain decibel level does not merely cause annoyance or discomfort; it can produce permanent damage to the hearing mechanism inside the ear.
Meaning of decibel level and threshold
The decibel (dB) is a unit used to express the intensity of sound. Because it is a logarithmic scale, an increase of 10 dB represents roughly a tenfold increase in sound intensity and a much greater increase in perceived loudness. For normal conversation, the sound level is about 50–60 dB, while heavy traffic may produce about 80–90 dB.
The term “threshold level” refers to the sound intensity above which irreversible or permanent hearing loss may begin to occur if exposure is sufficiently long or frequent. For occupational and environmental health purposes, a level of about 85 dB(A) is commonly regarded as the critical threshold for long-term exposure.
Noise level for permanent hearing damage
Research studies and health standards indicate that:
- Continuous exposure to noise levels of about 85 dB(A) or more for 8 hours a day, over several years, can cause Noise-Induced Hearing Loss (NIHL).
- At levels of 100 dB(A) and above, even shorter exposures can be harmful; the safe exposure time decreases as the noise level increases.
- Sound levels around 120–130 dB are often described as the “threshold of pain” and may cause immediate damage to delicate structures in the inner ear.
Initially, a person may experience temporary threshold shift (a temporary reduction in hearing sensitivity) after exposure to loud music, machines or explosions. However, repeated or continuous exposure above the threshold level eventually leads to permanent threshold shift, that is, permanent hearing impairment.
Examples of common noise levels
To understand the risk, some approximate examples are:
- Quiet room: about 30–40 dB
- Normal conversation: about 50–60 dB
- Busy traffic / noisy classroom: about 70–80 dB
- Heavy trucks, workshops, some factories: 85–95 dB
- Rock concerts, firecrackers, loudspeakers at close range: above 100 dB
Thus, workers in industries, traffic police personnel, people living near airports, railway lines or busy roads and youth regularly exposed to loud music are at greater risk of crossing the safe threshold level.
Health implications and need for control
Once hearing loss becomes permanent, it cannot be easily reversed by medicines or surgery. It leads to difficulties in communication, social isolation, reduced work efficiency and psychological stress. Therefore, Environmental Studies stresses that noise levels must be kept below the threshold level by proper urban planning, use of silencers, green belts, strict enforcement of noise standards and by promoting personal protection measures such as ear plugs or ear muffs for workers in noisy occupations.
Conclusion: The statement means that there is a critical decibel level (about 85 dB(A) for prolonged exposure), beyond which noise is not just irritating but becomes dangerous for the ear. Continuous or repeated exposure above this threshold can result in permanent hearing damage, making it essential to monitor, regulate and control noise pollution in our environment.