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The EPA has published information which describe noise “cause and effect” relationships for sensitive land uses.  These relationships are not standards because they do not account for the cost or feasibility of achieving these levels.  These relationships are provided for comparative purposes. 
  
 
   
 
Type of Comparison		  
Land Use		  
“Cause”		  
“Effect" (1)
 
IMPACT THRESHOLD (2)
Absolute Comparison
  (Based on overall 
  magnitude of the
  sound level)		 Residences
Hospitals		 55 dBA L(dn)
(OUTDOORS) 
  • 95%  sentence intelligibility (average) at 3.5m (11 ft.), normal voice
  • Indoors, 100% sentence intelligibility with a 5 dB margin of safety, normal voice
  • Consistent with available sleep criteria
 
65 dBA L(dn)
(OUTDOORS) 
  • 95% sentence intelligibility (average) at 1m (3 ft.), normal voice
  • Indoors, greater than 99% sentence intelligibility, normal voice (3)
  • Above available sleep criteria
 
75 dBA L(dn)
(OUTDOORS) 
  • 95% sentence intelligibility (average) at 0.7m (2ft), raised voice:  or at 1.5m (5ft), loud voice
  • Indoors, greater than 95% sentence intelligibility, normal voice (3)
  • Further above available sleep criteria
 
IMPACT THRESHOLD
Educational 55 dBA L(eq) (24-hours)
(Outdoor Level)
  • Outdoors
  • Indoors, with 5 dB margin of safety (3)
 
 
IMPACT THRESHOLD
Relative Comparison(4)
  (Based on the
  differrence between
  existing and project
  induced sound levels) 		 Residences Residences Intruding 
noise 5 dBA less than background noise, in the absence of the intruding noise 
  • 1% complaints
  • 15-20% highly annoyed
  • Noise essentially least important of various community factors
  • No expected community reaction
 
Intruding noise exceeds background by 5 dBA 
  • 5% complaints
  • 30-35% highly annoyed
  • Threats of legal action
 
Intruding noise exceeds background by 15 dBA
  • 15% complaints
  • 50-55% highly annoyed
  • 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 L(dn)” 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 and from industrial activity and trucking)
   50 dBA L(dn)
    • Normal suburban community (not located near industrial activity)
   55 dBA L(dn)
    • Urban residential community (not immediately adjacent to heavily traveled roads and industrial areas)
   60 dBA L(dn)
    • Noisy urban residential community (near relatively busy roads or industrial areas) 
   65 dBA L(dn)
    • Very noisy urban residential community 
   70 dBA L(dn)
 
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, Washingtion, D.C., March 1974.