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Posted By prads
Q1. You record a reading of 120 dBA with a SLM at a distance of 10 ft from a source. If you move to a distance of 20 ft from the source, what will be the new reading?
Q2. How long can an employee be exposed to continous noise levels of 110 dB?
Q3. If a dosimeter reading shows as 400% for an eight hour shift, what is the TWA in dB?
Any help?
Regards,
Pradeep
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Posted By Paul Leadbetter
Prads
What is the noise exposure limit at your location? We need this to answer questions 2 and 3.
Paul
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Posted By prads
Paul,
It is same as UK. First Action level at 85dB(A) and second action level at 90dB(A). Both averaged over 8 hours.
Regards,
P
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Posted By Lukasz
Prads
lower exposure action values:
– daily or weekly exposure of 80 dB;
– peak sound pressure of 135 dB;
upper exposure action values:
– daily or weekly exposure of 85 dB;
– peak sound pressure of 137 dB.
according to Noise at Work Regulation 2005
Page 3 of INDG362
http://www.hse.gov.uk/pubns/indg362.pdf
Regards
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Posted By Paul Leadbetter
Prads
The levels have been reduced in the UK to 80 and 85 dB(A) since the new noise regs in 2005.
Q1: 117 dB(A), I think, assuming a point source and hemispherical propogation.
Q2: 111 dB(A) exposure time is 3.75 minutes so 110 would be a little longer!
Q3: 96 dB(A).
Paul
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Posted By andhum
1. Noise attenuates at the rate of 50% when you double the distance. A doubling in noise level occurs at every 3dB(A). Therefore the noise level should be half that 20ft rather than 10 so it should be 117dB(A)
2. I presume you mean without hearing protection. The answer is never - use the HSE nomogram (just type in noise nomogram into google and you will get it)
3. My SLM's do not read in % terms so can you clarify what the 400% is referring to as it doesn't make too much sense?
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Posted By Lukasz
Q2: How long can an employee be exposed to continous noise levels of 110 dB?
"upper exposure action values:
– daily or weekly exposure of 85 dB;"
From HSE website http://www.hse.gov.uk/noise/reducenoise.htm
"Limit the time spent in noisy areas - every halving of the time spent in a noisy area will reduce noise exposure by 3 dB."
so daily exposure to 110 dB will be based on average 8 hours
8 hours = 110 dB
4 hours = 107 dB
2 hours = 104 dB
1 hour = 101 dB
30 minutes = 98 dB
15 minutes = 95 dB
7.5 minutes = 92 dB
3.75 minutes = 89 dB
1.875 minutes = 86 dB
1.875 x 60 seconds = 112.5 seconds
Less then 112.5 seconds
Paul
That is how I would calculate answer for Q2 based on guidance found right now.
Can you point me what I have done wrong?
Regards
LK
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Posted By Paul Leadbetter
Andhum
Your first answer is only correct if you assume that there is hemispherical propogation. In free space, doubling the distance reduces the noise level by a factor of 4 (the inverse square law) or 6 dB.
Paul
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Posted By andhum
Thanks Paul - I answered it from a simplistic point of view but bow to your superior knowledge!
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Posted By prads
Hi Paul,
Thanks again. How did u arrive at 96 dB(A) for the third question?
Rgds,
P
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Posted By andrew morris
Are we helping someone with course work here?
We should be being paid rates as this will be a budding competitor soon....
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Posted By Paul Leadbetter
Prads
Doubling the noise (200% of the limit) increases the level by 3 dB; doubling it again (t0 400% of the limit) increases it by another 3 dB, hence 96 dB.
Paul
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Posted By Paul Leadbetter
LK
You are right but I was working to the limits quoted by Prads.
Paul
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Posted By prads
Thank you all for the responses.
Andrew,
I was trying to solve a question paper on 'Occupational Hygiene' and I have understood that there is a lot of detail on which we need to work into. Broader concept is not enough.
Regards,
P
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