Selection of ear defenders

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

Octave (Hz) 125 250 500 1000 2000 4000 8000

11.6 18.7 27.5 32.9 33.6 36.1 35.8

4.3 3.6 2.5 2.7 3.4 3.0 3.8

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

Octave (Hz) 125 250 500 1000 2000 4000 8000

11.6 18.7 27.5 32.9 33.6 36.1 35.8

4.3 3.6 2.5 2.7 3.4 3.0 3.8

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

H M L method

SNR method

Most accurate method

H M L method

SNR method

Simplified methods

Octave Band Method

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

125 250 500 1K 2K 4K 8K

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)

125 250 500 1K 2K 4K 8K

7.3 15.1 25.0 30.2 30.2 33.1 32.0

Assumed protection is mean attenuation – 1 standard deviation

125 250 500 1K 2K 4K 8K

7.3 15.1 25.0 30.2 30.2 33.1 32.0

76.2 70.3 58.9 51.5 48.2 40.5 17.0

Level at ear = measured level – assumed protection

125 250 500 1K 2K 4K 8K

7.3 15.1 25.0 30.2 30.2 33.1 32.0

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

These are the specified correction factors for the A weighting

125 250 500 1K 2K 4K 8K

7.3 15.1 25.0 30.2 30.2 33.1 32.0

76.2 70.3 58.9 51.5 48.2 40.5 17.0

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

125 250 500 1K 2K 4K 8K

7.3 15.1 25.0 30.2 30.2 33.1 32.0

76.2 70.3 58.9 51.5 48.2 40.5 17.0

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:

8AC LL

LMMPNR

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

Octave (Hz) 125 250 500 1000 2000 4000 8000

11.6 18.7 27.5 32.9 33.6 36.1 35.8

4.3 3.6 2.5 2.7 3.4 3.0 3.8

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

8AC LL

LMMPNR

LC = 92.8 dB LA = 86.2dB M = 25 L = 15

22.866.92

152525PNR

So PNR = 19.5

PNR = 19.5

level experienced by the wearer = LA – PNR = 86.2 – 19.5 = 66.7 = 67 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

Octave (Hz) 125 250 500 1000 2000 4000 8000

11.6 18.7 27.5 32.9 33.6 36.1 35.8

4.3 3.6 2.5 2.7 3.4 3.0 3.8

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

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

With ear muffs, glasses, jewellery and long hair can interfere with the seals that keep noise out

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

And, of course, safety glasses can interfere with the seal on ear muffs

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

mike@diamondenv.co.uk

http://diamondenv.wordpress.com

Twitter: @diamondenv

Mike Slater

Mike Slater, Diamond Environmental Ltd. (mike@diamondenv.co.uk)

This presentation is distributed under the Creative Commons Attribution-NonCommercial-ShareAlike

UK:International Licence

Selection of ear defenders

Health & Medicine

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