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Mike Slater
First, consider technical performance
To do this, you’ll need information from the supplier of the proposed ear defenders
Supplier’s Information
Octave (Hz) 125 250 500 1000 2000 4000 8000
Mean attenuation (dB)
11.6 18.7 27.5 32.9 33.6 36.1 35.8
Standard deviation (dB)
4.3 3.6 2.5 2.7 3.4 3.0 3.8
Assumed protection (dB)
7.3 15.1 25.0 30.2 30.2 33.1 32.0
H = 32 M = 25 L = 15 SNR = 27
Peltor Optime 1
Supplier’s Information
Octave (Hz) 125 250 500 1000 2000 4000 8000
Mean attenuation (dB)
11.6 18.7 27.5 32.9 33.6 36.1 35.8
Standard deviation (dB)
4.3 3.6 2.5 2.7 3.4 3.0 3.8
Assumed protection (dB)
7.3 15.1 25.0 30.2 30.2 33.1 32.0
H = 32 M = 25 L = 15 SNR = 27
Assumed protection = mean attenuation – 1 standard deviation
Peltor Optime 1
Supplier’s Information
Octave (Hz) 125 250 500 1000 2000 4000 8000
Mean attenuation (dB)
11.6 18.7 27.5 32.9 33.6 36.1 35.8
Standard deviation (dB)
4.3 3.6 2.5 2.7 3.4 3.0 3.8
Assumed protection (dB)
7.3 15.1 25.0 30.2 30.2 33.1 32.0
H = 32 M = 25 L = 15 SNR = 27
Peltor Optime 1
Data for simplified methods
There are 3 methods:
Using octave band data
H M L method
SNR method
There are 3 methods:
Using octave band data
H M L method
SNR method
Most accurate method
There are 3 methods:
Using octave band data
H M L method
SNR method
Simplified methods
Octave Band Method
Octave band method 1. Undertake octave band analysis of noise
Octave band method 1. Undertake octave band analysis of noise
2. Obtain mean attenuation and standard deviation for ear defenders
Octave band method 1. Undertake octave band analysis of noise
2. Obtain mean attenuation and standard deviation for ear defenders
3. Calculate assumed protection in each octave band (mean – 1 standard deviation)
Octave band method 1. Undertake octave band analysis of noise
2. Obtain mean attenuation and standard deviation for ear defenders
3. Calculate assumed protection in each octave band (mean – 1 standard deviation)
4. Subtract assumed protection from noise levels in each octave band
Octave band method 1. Undertake octave band analysis of noise
2. Obtain mean attenuation and standard deviation for ear defenders
3. Calculate assumed protection in each octave band (mean – 1 standard deviation)
4. Subtract assumed protection from noise levels in each octave band
5. Correct for A weighting
Octave band method 1. Undertake octave band analysis of noise
2. Obtain mean attenuation and standard deviation for ear defenders
3. Calculate assumed protection in each octave band (mean – 1 standard deviation)
4. Subtract assumed protection from noise levels in each octave band
5. Correct for A weighting
6. Calculate assumed overall level at ear
Octave band method 1. Undertake octave band analysis of noise
2. Obtain mean attenuation and standard deviation for ear defenders
3. Calculate assumed protection in each octave band (mean – 1 standard deviation)
4. Subtract assumed protection from noise levels in each octave band
5. Correct for A weighting
6. Calculate assumed overall level at ear
7. HSE recommend a 4 dB(A) correction is applied to take account of "real world" factors
Octave band centre frequency (Hz)
125 250 500 1K 2K 4K 8K
Measured level (dB) 83.5 85.4 83.9 81.7 78 73.6 49
Measured levels 86.2 dB(A) 92.8 dB(C)
Here’s some data from a noise
survey
Octave band centre frequency (Hz)
125 250 500 1K 2K 4K 8K
Measured level (dB) 83.5 85.4 83.9 81.7 78 73.6 49
Assumed protection provided by ear defenders (dB)
7.3 15.1 25.0 30.2 30.2 33.1 32.0
Level at ear wearing ear defenders (dB)
A weighting correction
Level at ear wearing ear defenders (dBA)
Octave band centre frequency (Hz)
125 250 500 1K 2K 4K 8K
Measured level (dB) 83.5 85.4 83.9 81.7 78 73.6 49
Assumed protection provided by ear defenders (dB)
7.3 15.1 25.0 30.2 30.2 33.1 32.0
Level at ear wearing ear defenders (dB)
A weighting correction
Level at ear wearing ear defenders (dBA)
Assumed protection is mean attenuation – 1 standard deviation
Octave band centre frequency (Hz)
125 250 500 1K 2K 4K 8K
Measured level (dB) 83.5 85.4 83.9 81.7 78 73.6 49
Assumed protection provided by ear defenders (dB)
7.3 15.1 25.0 30.2 30.2 33.1 32.0
Level at ear wearing ear defenders (dB)
76.2 70.3 58.9 51.5 48.2 40.5 17.0
A weighting correction
Level at ear wearing ear defenders (dBA)
Level at ear = measured level – assumed protection
Octave band centre frequency (Hz)
125 250 500 1K 2K 4K 8K
Measured level (dB) 83.5 85.4 83.9 81.7 78 73.6 49
Assumed protection provided by ear defenders (dB)
7.3 15.1 25.0 30.2 30.2 33.1 32.0
Level at ear wearing ear defenders (dB)
76.2 70.3 58.9 51.5 48.2 40.5 17.0
A weighting correction -16.1 -8.6 -3.2 0 1.2 1 -1.1
Level at ear wearing ear defenders (dBA)
These are the specified correction factors for the A weighting
Octave band centre frequency (Hz)
125 250 500 1K 2K 4K 8K
Measured level (dB) 83.5 85.4 83.9 81.7 78 73.6 49
Assumed protection provided by ear defenders (dB)
7.3 15.1 25.0 30.2 30.2 33.1 32.0
Level at ear wearing ear defenders (dB)
76.2 70.3 58.9 51.5 48.2 40.5 17.0
A weighting correction -16.1 -8.6 -3.2 0 1.2 1 -1.1
Level at ear wearing ear defenders (dBA)
60.1 61.7 55.7 51.5 49.4 39.5 15.9
These values represent the A weighted levels at the ear when the ear defenders are worn
Octave band centre frequency (Hz)
125 250 500 1K 2K 4K 8K
Measured level (dB) 83.5 85.4 83.9 81.7 78 73.6 49
Assumed protection provided by ear defenders (dB)
7.3 15.1 25.0 30.2 30.2 33.1 32.0
Level at ear wearing ear defenders (dB)
76.2 70.3 58.9 51.5 48.2 40.5 17.0
A weighting correction -16.1 -8.6 -3.2 0 1.2 1 -1.1
Level at ear wearing ear defenders (dBA)
60.1 61.7 55.7 51.5 49.4 39.5 15.9
Level at ear wearing ear defenders = 64.9dB(A) Attenuation = 86 – 65= 21 dB(A)
Calculated level at ear wearing ear defenders = 65 dB(A)
Adjust by 4 db(A) to take account of “real world factors”
So level at ear is 69 dB(A)
Simplified Methods
HML high, medium and low
SNR “single number rating”
H M L Method
HML Method
1. Measure level in dB(A) = (LA)
2. Measure level in dB(C) = (LC)
3. If Lc - LA is >2:
4. Otherwise:
2
8AC LL
LMMPNR
2
4AC LL
MHMPNR
HML Method
The PNR is subtracted from the A weighted sound pressure level to give the level experienced by the wearer in dB(A)
Example
Measured levels
86.2 dB(A)
92.8 dB(C)
Example
Measured levels
86.2 dB(A)
92.8 dB(C)
Difference is 6.6 dB
> 2, so use L and M values
Supplier’s Information
Octave (Hz) 125 250 500 1000 2000 4000 8000
Mean attenuation (dB)
11.6 18.7 27.5 32.9 33.6 36.1 35.8
Standard deviation (dB)
4.3 3.6 2.5 2.7 3.4 3.0 3.8
Assumed protection (dB)
7.3 15.1 25.0 30.2 30.2 33.1 32.0
H = 32 M = 25 L = 15 SNR = 27
Peltor Optime 1
2
8AC LL
LMMPNR
LC = 92.8 dB LA = 86.2dB M = 25 L = 15
22.866.92
8
152525PNR
So PNR = 19.5
PNR = 19.5
level experienced by the wearer = LA – PNR = 86.2 – 19.5 = 66.7 = 67 dB(A)
Calculated level at ear wearing ear defenders = 67 dB(A)
Adjust by 4 db(A) to take account of “real world factors”
So level at ear is 71 dB(A)
SNR (Single Number Rating) Method
SNR Method
The effective A weighted sound pressure level at the ear is given by subtracting the SNR value from LC
Supplier’s Information
Octave (Hz) 125 250 500 1000 2000 4000 8000
Mean attenuation (dB)
11.6 18.7 27.5 32.9 33.6 36.1 35.8
Standard deviation (dB)
4.3 3.6 2.5 2.7 3.4 3.0 3.8
Assumed protection (dB)
7.3 15.1 25.0 30.2 30.2 33.1 32.0
H = 32 M = 25 L = 15 SNR = 27
Peltor Optime 1
SNR Method
Level at ear = LC – SNR = 92.6 – 27 = 65.6 = 66 dB(A)
SNR Method
Calculated level at ear wearing ear defenders = 66 dB(A)
Adjust by 4 db(A) to take account of “real world factors”
So level at ear is 70 dB(A)
Method Level at ear in dB(A)*
Octave band 69
HML 71
SNR 70
* Adjusted for “real world” factors
Don’t overprotect
Don’t overprotect Aim for a level at the ear between 60 and 80 dB(A)
HSE Guidance
From HSE publication L108 “Controlling noise at work”
We now need to consider other factors that will affect how well the ear defenders perform
These include compatibility with the:
• User • Job • Other PPE
Here are some examples (there are many others)
1. Compatibility with the user
Some people find wearing ear plugs uncomfortable
Compatibility with the user
Ear muffs can be uncomfortable to wear in hot conditions
Compatibility with the user
With ear muffs, glasses, jewellery and long hair can interfere with the seals that keep noise out
Compatibility with the user
2. Compatibility with the job
Wearing ear defenders can interfere with communication ....
Compatibility with the job
http://actrav.itcilo.org
.... and make it difficult to hear alarms and audible signals
Compatibility with the job
3. Compatibility with other PPE
Wearing ear muffs with safety helmets presents particular problems
Compatibility with other PPE
Helmet mounted muffs can significantly reduce the attenuation provided by the muffs
Compatibility with other PPE
And, of course, safety glasses can interfere with the seal on ear muffs
Compatibility with other PPE
Once suitable ear defenders have been selected, there are other important considerations to ensure that they are effective when they’re being used.
Once suitable ear defenders have been selected, there are other important considerations to ensure that they are effective when they’re being used. These include:
Fitting
Hearing protection zones
Enforcement
Care and maintenance
Training
http://www.slideshare.net/mikeslater
http://diamondenv.wordpress.com
Twitter: @diamondenv
Mike Slater
Mike Slater, Diamond Environmental Ltd. ([email protected])
This presentation is distributed under the Creative Commons Attribution-NonCommercial-ShareAlike
UK:International Licence