In environmental physics and public health, continuous sound levels become hazardous noise pollution for human beings at sound intensities above approximately what decibel (dB) level?

Introduction / Context:
This question evaluates your awareness of noise pollution and the decibel scale used to measure sound intensity levels. Noise pollution is not just about loud, momentary sounds; long term exposure to moderately high levels of noise can damage hearing, raise stress and affect overall health. Public health guidelines specify approximate decibel levels beyond which noise is considered harmful, especially for continuous exposure. Knowing these thresholds is useful for both exams and daily life decisions, such as using ear protection in noisy environments.

Given Data / Assumptions:

• We are comparing different continuous sound levels expressed in decibel (dB).
• We focus on levels where sound becomes hazardous noise pollution for normal human ears.
• Options range from low environmental levels (30 dB) to very high levels (120 dB).
• We assume typical guidelines where prolonged exposure is considered.

Concept / Approach:
The decibel scale is logarithmic, so each increase of 10 dB represents a tenfold increase in sound intensity. Soft conversation may be around 50 to 60 dB, busy traffic can be around 70 to 85 dB, and rock concerts or sirens may reach 110 dB or more. Health agencies often indicate that long term exposure to sound above roughly 80 to 85 dB can lead to hearing damage and is treated as noise pollution. Very short term exposure to extremely loud sounds such as 120 dB is immediately painful, but the standard exam answer for the threshold of hazardous noise in ordinary settings is usually above 80 dB.

Step-by-Step Solution:
Step 1: Recognise that 30 dB corresponds roughly to a quiet library or soft whisper, which is not hazardous. Step 2: Note that 50 dB is comparable to normal conversation, which again is not typically considered dangerous noise. Step 3: Understand that 80 dB to 90 dB levels correspond to heavy traffic, loud workplace machinery or busy urban environments, where long term exposure can damage hearing. Step 4: Remember that many safety guidelines treat levels above about 80 dB as potentially harmful if exposure is prolonged, marking the onset of hazardous noise pollution. Step 5: Recognise that 120 dB is an extremely loud and painful level, but the exam threshold for when ordinary environmental sound becomes noise pollution is most commonly taken as above 80 dB.

Verification / Alternative check:
As a simple check, think about common experiences. People generally do not complain about noise pollution in places with 30 or 50 dB sound levels; these are typical for quiet residential areas or offices. Complaints and health concerns rise in places like factories, traffic junctions or loud music venues, where sound levels often exceed 80 dB. Hearing protection rules in workplaces also tend to become strict in this range. Thus, above 80 dB fits both practical experience and textbook guidance.

Why Other Options Are Wrong:
Above 120 dB describes extremely loud and painful sounds but is much higher than the commonly accepted threshold for hazardous noise pollution in everyday environments. Above 50 dB is too low, since normal speech and many harmless daily activities produce this level of sound. Above 30 dB is also far too low, covering almost all ordinary environments; calling this hazardous would not match scientific or regulatory practice.

Common Pitfalls:
Students sometimes focus only on the most dramatic number (120 dB) and assume that is the threshold for danger. While such levels are indeed very dangerous, the exam phrase noise pollution usually refers to continuous or frequent exposure levels around 80 dB and above. Another mistake is to ignore that the scale is logarithmic, meaning a change of 30 dB represents a huge difference in intensity. Remembering that normal conversation is around 50 to 60 dB and that harmful environmental noise starts above about 80 dB will guide you to the correct answer.

Final Answer:
Sound becomes hazardous noise pollution for humans at levels above about 80 dB when exposure is prolonged.