EPA Community Noise Cause-And-Effect Relationships
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Type of Comparison |
Land Use |
“Cause” |
“Effect[1]” |
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Absolute comparison (Based on overall magnitude of the sound level) |
Residences Hospitals |
55 dBA Ldn (OUTDOORS) |
IMPACT THRESHOLD[2] 1. 95% sentence intelligibility (average) at 3.5m (11 ft.), normal voice 2. Indoors, 100% sentence intelligibility with a 5 dB margin of safety, normal voice[3] 3. Consistent with available sleep criteria |
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65 dBA Ldn (OUTDOORS) |
1. 95% sentence intelligibility (average) at 1m (3 ft.), normal voice 2. Indoors, greater than 99% sentence intelligibility, normal voice3 3. Above available sleep criteria |
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75 dBA Ldn (OUTDOORS) |
1. 95% sentence intelligibility (average) at 0.7m (2ft), raised voice: or at 1.5m (5ft), loud voice 2. Indoors, greater than 95% sentence intelligibility, normal voice3 3. Further above available sleep criteria |
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Educational Uses |
55 dBA Leq (24) (OUTDOORS) |
IMPACT THRESHOLD outdoors IMPACT THRESHOLD, with 5 dB margin of safety, indoors3 |
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Relative comparison[4] (Based on the difference between existing and project induced sound levels) |
Residences |
Intruding noise 5 dBA less than background noise, in the absence of the intruding noise |
IMPACT THRESHOLD 1. 15% complaints 2. 15-20% highly annoyed 3. Noise essentially least important of various community factors 4. No expected community reaction |
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Intruding noise exceeds background by 5 dBA |
1. 5% complaints 2. 30-35% highly annoyed 3. Threats of legal action |
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Intruding noise exceeds background by 15 dBA |
1. 15% complaints 2. 50-55% highly annoyed 3. Vigorous community action expected |
[1] All percentages shown are average percentages; specific percentage values depend upon community attitudes towards the noise source, prior experience with similar noise sources, plus other factors not related to the actual noise level.
[2] “Requisite to protect the public health and welfare with an adequate margin of safety.”
[3] Windows assumed open, resulting in outdoor-to-indoor noise insulation of 15 dBA.
[4] This presentation of EPA conclusions condenses the EPA’s “normalized Ldn,,” to a single IMPACT THRESHOLD tabulation. This condensation is consistent with the following average background noise levels:
- Quiet suburban or rural community (remote from large cities 50 dBA Ldn
and from industrial activity and trucking)
- Normal suburban community (not located near industrial activity) 55 dBA Ldn
- Urban residential community (not immediately adjacent to heavily 60 dBA Ldn
traveled roads and industrial areas)
- Noisy urban residential community (near relatively busy 65 dBA Ldn
roads or industrial areas)
- Very noisy urban residential community 70 dBA Ldn
Source: U.S. Environmental Protection Agency, “Information on Levels of Environmental Noise Requisite to Protect Public Health and Welfare with an Adequate Margin of Safety,” Report 550/9-74-004, Washington, D.C., March 1974.