Noise, Vibration, and Other Physical Pollution Control
What this domain tests
Standards by area class and boundary type, plus propagation arithmetic. The calculation questions are usually two-source addition and distance attenuation.
Standards
- GB 3096-2008 声环境质量标准, day/night limits in dB(A): class 0 50/40; class 1 55/45; class 2 60/50; class 3 65/55; class 4a 70/55; class 4b 70/60. Class 4a covers road traffic, 4b rail.
- GB 12348-2008 industrial boundary: class 1 55/45, class 2 60/50, class 3 65/55, class 4 70/55. At night, a frequent or occasional maximum exceeding the limit by 10 dB(A) or more counts as non-compliant.
- GB 12523-2011 construction boundary: 70 day, 55 night.
- GB 22337-2008 social and commercial sources; GB 10070-88 urban vibration, 75 day and 72 night.
- 噪声污染防治法 took effect 2022-06-05 and adds duties on transport, construction and social sources.
Metrics and propagation
- Energy addition: L = 10 log (sum of 10 raised to 0.1 Li). Two equal sources add 3 dB; ten equal sources add 10 dB.
- Point source distance attenuation: L2 = L1 − 20 log(r2/r1), so doubling distance loses 6 dB.
- Line source, such as a road: L2 = L1 − 10 log(r2/r1), so doubling distance loses 3 dB.
- Control hierarchy: source reduction, then path control by enclosure, silencers, barriers and absorptive linings, then receptor protection.
Worked example
Two identical fans each produce 85 dB(A) at 1 m. The boundary lies 40 m away in a class 2 area with a night limit of 50 dB(A).
- Combined level at 1 m = 85 + 10 log 2 = 88 dB(A).
- Distance attenuation = 20 log(40/1) = 32 dB, so the boundary level is 88 − 32 = 56 dB(A), treating them as a point source.
- The night limit is 50 dB(A), so the exceedance is 6 dB.
- Required insertion loss is at least 6 dB; adding a 3 dB design margin means specifying enclosures and silencers rated at 9 dB or better. Reaching that by heightening the wall alone is usually impossible.
Traps
- Averaging sound levels arithmetically instead of adding them energetically.
- Applying the 20 log point-source law to a road; a road is a line source at 10 log.
- Ignoring the night maximum-level rule for intermittent sources.
- Mixing class 4a and 4b limits.
- Placing a boundary measurement point inside the plant or less than 1.2 m above ground.
- Treating vibration limits as dB(A); they are stated as VLz in dB.