What is the noise level that can cause permanent impairment of hearing ability of human beings ?

Explanation

### Step-by-Step Solution:

1. **Understanding Noise Levels**: Noise levels are measured in decibels (dB), which quantify the amplitude of sound. Higher decibel levels indicate louder sounds.

2. **Identifying Thresholds for Hearing Damage**: Research indicates that sounds above 70 dB can start to cause damage to hearing. This is the threshold where potential harm begins.

3. **Recognizing Severe Damage Levels**: Sounds that reach 120 dB are significantly louder and can cause serious damage to hearing. This level is often associated with loud environments like concerts or heavy machinery.

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