The International Labour Organization (ILO) signed a convention at its 63rd conference, which defines noise in Article 3 as “all sounds that cause hearing loss or lead to other health hazards.”

The Impact of Noise on Hearing

The extent of noise impact depends on the duration of exposure, the frequency and intensity of the noise, whether it is intermittent or continuous, and personal characteristics. There are primarily three effects observed in the hearing system as a result of noise exposure:

1. Acoustic damage or trauma
2. Temporary threshold shift
3. Permanent threshold shift

The first effect is described as auditory fatigue. As the intensity and loudness of the sound increase, so does the auditory fatigue. The biological effects of transient noise are somewhat different from those of continuous noise. The inner ear is partially protected from the effects of continuous noise due to the acoustic reflex. This reflex allows the muscles in the inner ear to contract in response to sounds above 90 dB, enabling resistance to sound intensity. High-intensity transient noise reaches the cochlea before the acoustic reflex can occur. Direct mechanical damage affects the hair cells in the organ of Corti in the cochlea, and these effects are irreversible. A sound pressure level of 140 dB can lead to sudden and irreversible hearing loss, known as acoustic trauma.

Temporary Hearing Losses

Temporary hearing losses occur after prolonged exposure to noise and can improve after a certain period of rest. For instance, the recovery time required to resolve an approximately 18-20 dB hearing loss resulting from 100 minutes of exposure to a noise level of 90 dB (A) is also approximately 1000 minutes. It is indicated that a recovery period at least ten times the duration of exposure is necessary for the resolution of the hearing loss. It is known that as the noise level increases, both the resulting hearing loss and recovery time also increase. In noisy environments, it is often not possible for workers, especially in the industry, to have these recovery times. Workers who have a maximum rest period of 16 hours after an 8-hour exposure develop these hearing losses in a cumulative manner, leading to continuous hearing losses. This physical energy exerted on the auditory receptors over a long period causes damage to these receptors, leading to irreversible neural type hearing losses.

The Effects of Noise on Health

Studies have shown a significant increase in cortisol levels due to exposure to noise levels of 90 dB (A) for 8 hours and 84 dB (A) for 24 hours. It has also been reported that abnormally elevated cortisol levels lead to eosinopenia, hypertension, osteoporosis, and stress ulcers, as well as causing an imbalance of adrenaline and noradrenaline, which contributes to cardiovascular diseases.

Since human speech frequencies are between 500-3000 Hz, significant difficulties in speech perception do not arise until frequencies around 3000 Hz are affected. Therefore, audiometric examinations conducted before speech frequencies are affected are crucial for early diagnosis and protection.

Characteristics of Hearing Loss Caused by Noise:

1. Occurs with sounds exceeding 90 dB.
2. Hearing loss affects both ears bilaterally.
3. The first hearing loss in the ear occurs at a frequency of 4000 Hz, subsequently affecting speech frequencies.
4. The resulting hearing loss is of the neural type and has no definitive cure. Therefore, protection from noise is extremely important.

Effects and Types of Noise

Physical effects:

• Causes damage to the auditory system and ear canals.

Physiological effects:

Intermittent and sudden noise triggers an immediate adrenaline release;

• Increases heart rate,
• Increases respiration rate,
• Elevates blood pressure.

Psychological effects:

• Causes restlessness, insomnia, irritability, and concentration difficulties in individuals.
• May lead to changes in character.
• Triggers anxiety, depression, and psychosomatic disorders.

While significant advances have been made in medicine, the treatment of hearing losses caused by noise remains extremely difficult. Preventive measures are essential. Solutions include the development of appropriate work areas, the use of ear protection, and adherence to occupational health standards. Thus, the issue of hearing loss due to noise is critical to evaluate, especially in the industrial sector.