12. Octave band method
1. Undertake octave band analysis of noise
2. Obtain mean attenuation and standard deviation for ear
defenders
13. 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)
14. 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
15. 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
16. 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
17. 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
18. Octave band centre
frequency (Hz)
Measured level (dB)
Measured levels
125
83.5
250
85.4
500
83.9
86.2 dB(A)
1K
2K
81.7
4K
78
8K
73.6
92.8 dB(C)
Here’s some data
from a noise
survey
49
19. 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)
20. 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
21. 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
A weighting correction
Level at ear wearing ear
defenders (dBA)
Level at ear = measured level – assumed protection
17.0
22. 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
23. 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
25. 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)
28. HML Method
1. Measure level in dB(A) = (LA)
2. Measure level in dB(C) = (LC)
3. If Lc - LA is >2:
M L
PNR M
L C L A 2
8
4. Otherwise:
H M
PNR M
L C L A 2
4
29. HML Method
The PNR is subtracted from the A
weighted sound pressure level to give the
level experienced by the wearer in dB(A)
35. PNR = 19.5
level experienced by the wearer = LA – PNR
= 86.2 – 19.5
= 66.7
= 67 dB(A)
36. 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)
41. 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)
58. Compatibility with other PPE
Helmet mounted
muffs can significantly
reduce the attenuation
provided by the muffs
59. Compatibility with other PPE
And, of course, safety
glasses can interfere
with the seal on ear
muffs
60. Once suitable ear defenders have
been selected, there are other
important considerations to
ensure that they are effective
when they’re being used.
61. 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:
62. Fitting
Hearing protection zones
Enforcement
Care and maintenance
Training
64. Mike Slater, Diamond Environmental Ltd. (mike@diamondenv.co.uk)
This presentation is distributed under the Creative Commons
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