“Real world” noise exposure beneath hearing protectors : a scattered international practice Pierre Canetto, Nicolas Trompette Institut National de Recherche et de Sécurité, France Acoustics’08, Paris June-July 2008

Acoustics’08 2 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

Acoustics’08 3 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 values LEX,8h = 87 dB(A) Lpc=140 dB (C)

Acoustics’08 4 Exposure beneath HPD : evaluation method (EN ISO ) Ambiant exposure HPD attenuation Exposure beneath HPD = minus equals -

Acoustics’08 5 Gap between real-world and laboratory- measured HPD attenuation values Ordinates : difference values in dB; abcissae : studies Criteria for a recommended standard, Occupational noise exposure – revised criteria 1998, US department of health and human services, June 1998

Acoustics’08 6 Ranging the discrepancy parameters Family ParametersInvolved partyActions Human factors Bad wearing, HPD adaptation, HPD care... CompaniesChoose 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,frequenc y range,subjectiv e character... Research and standardization organizations Improve subjective tests, develop objective tests,developon -site individual tests

Acoustics’08 7 HPD non-wearing time HP attenuation 30 dB HP attenuation 20 dB HP attenuation 10 dB + Working constraints: Gestures, jaws movements, HPD removal...

Acoustics’08 8 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

Acoustics’08 9 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

Acoustics’08 10 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

Acoustics’08 11 A scattered international practice Sweden, Finland, Spain, Poland, Slovakia Great- Britain Germany 1 Portugal, France 2 Italy 1 USA General method NoneGlobal derating Statistic al range enlarge ment Derating ratio, « Subject-Fit » method Correcti on value 4 dB for all kinds of HPD Earplugs : 9 dB Earmuffs : 5 dB Individual moulded earplugs : 3 dB 2 σ 3 σWhen 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

Acoustics’08 12 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.

Acoustics’08 13 « 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.

Acoustics’08 14 « 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

Acoustics’08 15 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 %

Acoustics’08 16 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 ?

Acoustics’08 17 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

Acoustics’08 18 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