Air & Noise Compliance

EPA Community Noise Cause-And-Effect Relationships

Type of



Land Use









Absolute comparison

(Based on overall magnitude of the sound level)



55 dBA Ldn



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



65 dBA Ldn


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



75 dBA Ldn


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


Educational Uses

55 dBA Leq (24)



IMPACT THRESHOLD, with 5 dB margin of safety, indoors3

Relative comparison[4]

(Based on the difference between existing and project induced sound levels)


Intruding noise 5 dBA less than background noise, in the absence of the intruding noise


1. 15% complaints

2. 15-20% highly annoyed

3. Noise essentially least important of various community factors

4. No expected community reaction



Intruding noise exceeds background by 5 dBA

1. 5% complaints

2. 30-35% highly annoyed

3. Threats of legal action



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.