“Real world” noise exposure beneath hearing protectors : a scattered international practice

Pierre Canetto, Nicolas TrompetteInstitut National de Recherche et de Sécurité, France

Acoustics’08, Paris June-July 2008

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Lecture development

• HPD attenuation is a topical issue in noise exposure assessment

• Various methods are available to reach HPD « real-world » attenuation values

• All methods present advantages and drawbacks

• Priority should be given to prevention principles and product performance

• Trying to find a « short term » proposal

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The « limit values » in the new European noise regulation

“When applying the exposure limit values, the determination of the worker's effective exposure shall take account of the attenuation provided

by the individual hearing protectors worn by the worker”.

2003/10/EC Directive : exposure limit valuesLEX,8h = 87 dB(A)

Lpc=140 dB (C)

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Exposure beneath HPD : evaluation method (EN ISO 4869-2)

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Série1

Ambiant exposure

HPDattenuation

Exposurebeneath

HPD

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Gap between real-world and laboratory-measured HPD attenuation values

labelled minus real-world attenuations

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earmuffs

premoulded

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Ordinates : difference values in dB; abcissae : studiesCriteria for a recommended standard, Occupational noise exposure – revised criteria 1998,

US department of health and human services, June 1998

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Ranging the discrepancy parameters

Family Parameters Involved party Actions

Human factors

Bad wearing, HPD adaptation, HPD care...

Companies Choose suitableHPD, train workers

Product quality

Manufacturing variability, ageing, human ear fitting...

Research and standardization organizations Manufacturers

Work out quality criteria... Products improvement

Laboratory tests

Noise levels,frequency range,subjective character...

Research and standardization organizations

Improve subjective tests, develop objective tests,developon-site individual tests

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HPD non-wearing time

HP attenuation 30 dBHP attenuation 20 dBHP attenuation 10 dB

+ Working constraints: Gestures, jaws movements, HPD removal...

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Compensation methods : 1) derating

• Absolute derating : decrease the declared attenuation from a global amount The amount can be different according to

the HPD kind• Proportional derating : the declared

attenuation is decreased fromapercentage The amount of the % can be different

according to the HPD kind

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Compensation methods : 2) « Subject Fit » tests

• In EN harmonized standards, subjects used for HPD tests are trained and the HPD good fitting is checked

• New ANSI standards propose to use untrained subject who will fit themselves the HPD without an expert hel

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Compensation methods : 3) « statistical enlargement »• Standardized EN methods give

statistical results• The HPD attenuation can be calculated

by subtracting more or mless standard deviations to the mean

standard deviations

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ear muffs foam ear plugs premolded ear plugs

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A scattered international practice

Sweden, Finland, Spain,

Poland, Slovakia

Great-Britain

Germany1 Portugal, France2

Italy1 USA

General method

None Global derating

Global derating

Statistical range enlargement

Statistical

range enlargement

 

Derating ratio, « Subject-Fit » method

Correction value

4 dB for all kinds of HPD

Earplugs : 9 dBEarmuffs : 5 dBIndividual moulded earplugs : 3 dB

2 σ 3 σ When SF values are not available NRR becomes : Earmuffs : 0.75 NRR, Formable earplugs : 0.5 NRR All other earplugs : 0.3 NRR

1 changes in progress; 2 publishing in progress

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Derating method

• Advantages : simple and allows an immediate implementation.

• Drawbacks : doesn’t make a clear difference between human and

product factors. doesn’t take into account the product quality dispersion. the global derating factors don’t allow to make a

difference between various HPD of the same kind, risk of overprotection with « good » HPD used correctly.

• Remarks : derating could impede progress in products

development. The implementation of this method would ask for an

international agreement on classification of HPD kinds and derating values.

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« Subject Fit » method

• Advantages : allows to make a difference between HPD of the same

kind. doesn’t need to harmonize HPD classification and

derating values in various countries.• Drawbacks :

The main risk is that it could « endorse » the non-training of workers.

doesn’t take into account the product quality dispersion. • Remarks :

In a short term, it would need an official European approval of the corresponding standard.

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« Statistical enlargement » method• Advantages :

allows to make a difference between HPD of the same kind.

The method is more suitable for a product qualification It is of possible immediate use. It doesn’t need to harmonize HPD classification and

derating values in various countries. • Drawbacks :

the method is complex for a non specialist.• Remarks

It only needs an agreement about the number of standard deviations to subtract.

Because it is dedicated to trained workers, it needs to go with a strong incentive to workers training

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A methodological problem : mixing all discrepancy causes

Distribution of observed causes of exposure to noise higher than calculated by dint of octave-band method - ear muffs

Kotarbińska E.et al. , " Investigation of exposure to noise of workers wearing ear-muffs"proceedingsof the 36th meeting of Vibroacoustics, Wisla, Poland, February 2008

bad technical condition of ear-muffs :33 %

not identified causes : 29 %

mixed causes : 8%

wearing spectacles : 8%

incorrect selection of HP : 7%

incorect way of wearing : 15 %

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A main prevention risk : discourage the workers training

• Making the lack of training « official »• Which is still mandatory in regulations

EU :“the employer shall ensure that workers [...] receive information and training [...] concerning, in particular[...] the correct use of hearing protectors”

US :“The employer shall provide training in the use and care of all hearing protectors provided to employees”; “The employer shall ensure proper initial fitting and supervise the correct use of all hearing protectors”.

• Wouldn’t this solution discourage companies from training their workers ?

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An industrial and prevention risk : discourage manufacturers efforts

• « good » and « bad » products shouldnot be treated in the same way

• The compensation method should make a difference between the product and its use

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Conclusion

• The question of HPD « real world » attenuation needs a short-term answer

• Attention should be paid not to spread a method which could go against prevention principles

• An international minimum agreement would be highly desirable at least at a European scale