WHO criteria

[Federico Miyara <fmiyara@xxxxxxxxxxxxx>]

Dear friends,

The following is a list of noise and acoustical figures recommended
by the World Health Organisation. The figures are the maximum 
recommended, except otherwise noted. Find below the explanation of the
abbreviations.


Limits
------

100 - 130 dBA           Auditory disconfort
130 - 140 dBA           Physical damage risk (e.g., ear 
                        drum rupture)
130 dBA                 Acute pain
70 dBA Leq24            Negligible hearing impairment 
30 dBA Leq              Excellent intelligibility
45 dBA Leq              Complete intelligibility
40 - 55 dBA Leq         Reasonably good intelligibility
< 0.6 s Trev            Adequate intelligibility
0.25 - 0.5 s Trev       Adequate intelligibility for the 
                        hearing impaired
S/N > 0 dB              Speech comprehension  
S/N > 10 dB - 15 dB     Speech comprehension for foreign
                        languages, complicated messages
100 dBA Leq4            Concerts
90  dBA Leq4            Discotheques
140 dB peak             Impulsive sounds
ASPL < 80 dBA           Toys, at child's ear
CSPL < 130 dBC          Toys, at child's ear
30 dBA Leq              Interior noise while sleeping
40 - 45 dBA Lmax (fast) Noisy isolated events while sleeping    
45 dBA Leq              Exterior noise while sleeping (with
                        open windows, assuming 15 dB reduction
35 dBA Leq              Hospital rooms
45 dBA Lmax (fast)      Noisy isolated events, Hospital rooms  
50 - 55 dBA Leq         Outdoors, daytime
40 - 50 dBA Leq         Outdoors, nighttime
1 s Trev                School bars
55 dBA Leq              School patios

Besides, if LeqC - LeqA > 10 dBA, then 5 dBA should be added 
to LeqA if LeqA < 60 dBA and 3 dBA if LeqA > 60 dBA

 
Abbreviations
-------------

Leq:   Equivalent level during measurement
Leq24: Equivalent level extended to a 24 hour period of time
Leq4:  Equivalent level extended to an 8 hour period of time 
LeqA:  Equivalent level with an A frequency weighting
LeqC:  Equivalent level with a  C frequency weighting 
Lmax:  Maximum time weighted level (fast, slow, impulse)
Peak:  Maximum instantaneous level
fast:  .125 s time weighting
slow:  1 s time weighting  
SPL:   Sound presure level
dBA:   Decibel with an A frequency weighting
dBC:   Decibel with a  C frequency weighting
S/N:   Signal to noise ratio, usually in decibels
Trev:  Reverberation time (how long lasts sound after turning 
       its source off)

This informtion was taken from the book on Community Noise edited by
Berglung and Lindvall, published by the Karolinska Institute, Sweden, 
available from the Stockholm University.

Best regards.

Federico Miyara

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