Quiet-List 1997

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Safe acoustical levels for public display of fireworks and other displays



>Date: Sun, 31 Aug 1997 00:28:47 +0530
From: J Balamurugan <bala@webindia.com>
>Organization: WebIndia Internet Services Pvt Ltd.
>To: fmiyara@unrctu.edu.ar
>CC: kali@webindia.com
>Subject: Safe acoustical levels for public display of fireworks and other
displays
>
>Dear sir,
>         We are a reasearch and development team working on designing
>safe fire crackers within the approved noise pollution levels. Can you
>send us some info on what are the allowed or safe decibel levels for a
>human being to operate in a fireworks environment or can you guide us to
>some resources.



Dear J Balamurugan,

It's difficult to answer your question in a definite way. In 1968, 
CHABA (The Committee on Hearing, Bioacoustics and Biomechanics) 
proposed some criteria regarding exposure to impulsive noises such 
as gunfire noise or firecrackers. These criteria were obtained from
surveys on the effect of fire guns.

They defined "hearing loss" according to the following table:


   |-----------------------------------------------------| 
   | Frequency        |  1000 Hz  |  2000 Hz  |  3000 Hz |
   |-----------------------------------------------------| 
   | Threshold shift  |   10 dB   |   15 dB   |   20 dB  |
   |-----------------------------------------------------|


Then they defined A-duration exposure for impulsive sounds outdoors,
and B-duration exposure for impulsive sounds in reverberant areas. 
As firecrackers are usually used outdoors, the A criterion applies.

This criterion intends to protect 95% of the population from hearing 
loss as high as that in the table, and says that for occasional 
impulses or blasts, 167 dB peak pressure level (that is, maximum 
pressure deviation logarithmically related to 0.000020 Pascals) is 
the maximum allowable value for pulse durations exceeding 2 msec.
For shorter pulses, 6 dB may be added for each ten-fold duration 
reduction. For example. 0.02 msec pulses (that is a hundred times 
shorter) may be (according to the criterion) 167 + 6 + 6 = 179 dB.
For a larger number of pulses a day, the whole criterion is reduced 
by 10 dB each 100-fold increase in the number of pulses.

The criterion is shown in the following chart:      



  max.  peak
   pressure 
      dB

      |
  179 |
      |\
      |  \
      |    \
      |      \
      |\       \
  167 |  \       \__________________ occasional pulses
      |    \           
      |      \        
      |        \        
  157 |          \__________________ 100 pulses/day 
      |
      |  
      |____________________________________     duration                     
                                            (msec, log scale)
      0.02       2 



Now, USA OSHA and other organisations limit to 140 dB the maximum 
allowed peak pressure level, so I would take this limit as the 
preferred one when it is lower than CHABA's one.

This information is taken from the book Noise and Vibration Control
Engineering, by Beranek-Ver (John Wiley, New York, 1992).

If possible, please inform us about the peak pressure level of different
kinds of firecrackers at several distances. Thank you.

Regards,

Federico Miyara  


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