2012-06-01 12:00 - Messages

Optimal suspension characteristics for the reduction of the vibrations transmitted by a small pneumatic hammer.

This paper describes a systematic approach for optimizing suspension systems to reduce the vibrations transmitted to workers by hand-held power tools. The optimization is based on modeling tool-operator interactions using a mobility scheme. The tool is modeled as a vibration generator, and its internal impedance is included. A hand–arm impedance matrix is used to model the operator upper limbs. The mobility model is used to identify the optimal suspension characteristics, which in our study were the set of parameters that minimizes the frequency-weighted acceleration at the hand–tool interface. Different handling conditions (one and two hands) and different working cycles with the same tools can be included in the optimization process. The constraints derived from the limitation on the increase in the tool mass and the static deflection of the mounting system under the working loads are also considered. The proposed method has been applied to the reduction of the vibrations transmitted to the operator by a small pneumatic hammer. The designed system reduced the worker's exposure so that it is within the limits of the EU directive. The agreement between the model predictions and the measured suspension performances validates the effectiveness of this approach.

Source; Saggin, B., Scaccabarozzi, D., Tarabini, M. Optimized design of suspension systems for hand–arm transmitted vibration reduction. Journal of Sound and Vibration; Volume 331, Issue 11, 21 May 2012, Pages 2671–2684

http://dx.doi.org/10.1016/j.jsv.2012.01.024

http://www.sciencedirect.com/science/article/pii/S0022460X12000703

Buy-Quiet Process Roadmap REVISED

The NASA Buy-Quiet process helps you develop requirements for low-noise equipment that is efficient, cost-effective, and, most importantly, safe for the people who work with and around it. Like most processes, this one can get pretty long and complicated, so use this roadmap to find your way through it! The Roadmap is a tool that supports the procurement of low-noise products, which is an important aspect of a strong engineered noise controls program. It is assumed that the Roadmap, and the Buy-Quiet program that guides its application, will be implemented in the context of a comprehensive hearing conservation program that includes other classical strategies for controlling employee noise exposure and preventing noise-induced hearing loss.

Source : EARLAB, the NASA Auditory Demonstration Laboratory. Educational tools and resources that energize the practice of hearing conservation. http://buyquietroadmap.com/buy-quiet-purchasing/

http://buyquietroadmap.com/buy-quiet-purchasing/buy-quiet-process-roadmap/

Une démarche de mise en conformité réglementaire de l’exposition au bruit des travailleurs

L'évaluation de l'environnement professionnel est une condition indispensable pour satisfaire à l'obligation de sécurité auxquels les employeurs sont soumis vis-à-vis de leurs employés. Il lui faut ensuite mettre en œuvre des moyens de prévention en adéquation avec les risques identifiés.
La réglementation impose le contrôle de l'exposition au bruit des travailleurs tous les cinq ans ou dès la survenue d'une modification profonde des installations, puis précise les dispositions à prendre en cas de dépassement des différents seuils limites d'exposition. Ces obligations sont d'autant plus importantes que le risque de surdité professionnelle n'est pas maîtrisé et qu'un français sur deux se déclare gêné par l'ambiance sonore au sein de son entreprise tandis que seulement quatre actifs sur dix disent avoir des protections auditives à leur disposition.

Source : Esteves, B. ; Blanchet, V. Archives des maladies professionnelles et de l'environnement. 04/2012, pp. 138-139.
http://dx.doi.org/10.1016/j.admp.2012.02.046

The ANSI S12.42 methods proposed by EPA’s provide consistent and reproducible results

This study tests the ANSI S12.42 methods with a range of hearing protection devices measured in field conditions. The average IPILs (impulse peak insertion loss) increased with peak pressure and ranged between 20 and 38 dB. For some protectors, significant differences were observed across protector examples of the same model, and across insertions. The EPA's (U.S. Environmental Protection Agency) proposed methods provide consistent and reproducible results. The proposed impulse NRR (noise reduction rating) rating should utilize the minimum and maximum protection percentiles as determined by the ANSI S12.42-2010 methods.

Source : Murphy, W.J. et al. Measurement of impulse peak insertion loss for four hearing protection devices in field conditions. International Journal of Audiology; February 2012, Vol. 51, No. S1, Pages S31-S42.

http://informahealthcare.com/doi/abs/10.3109/14992027.2011.630330

Vibrations, exiguïté, faible marge de manoeuvre

Comment améliorer le poste de conduite du métro de Montréal?
Ce document est destiné aux intervenants en santé et en sécurité du travail, aux ergonomes, aux ingénieurs et à toute personne concernée par l'amélioration d'un poste de travail dans un contexte de faible marge de manoeuvre.
Il décrit sommairement tant la démarche technique que la collaboration qui ont permis d'améliorer le poste de conduite du métro de Montréal dont le siège, l'espace restreint et les vibrations généraient de l'inconfort chez les opérateurs. À l'issue de l'étude, des modifications ont pu être apportées à la loge et un prototype de siège constituant le meilleur compromis possible pour améliorer la situation a été proposé.

Source : http://www.irsst.qc.ca/-publication-irsst-vibrations-exiguite-faible-marge-de-manoeuvre-r-721.html

The presence of a backrest changes the biodynamic response of the seated body and should be taken into account

This study investigated the apparent mass and cross-axis apparent mass of the human body exposed to random vibration (0.2 to 20 Hz) in all 15 possible combinations of four magnitudes (0, 0.25, 0.5 and 1.0 ms–2 r.m.s.) of fore-and-aft vibration and the same four magnitudes of vertical vibration. The human body has a nonlinear response to wholebody vibration: a softening response as the magnitude of vibration increases. The nonlinearity is apparent when the body is excited at varying magnitudes of single-axis vibration and when the body is excited by a fixed magnitude of vibration in one axis and varying magnitudes of vibration in another axis. The presence of a backrest changes the biodynamic response of the seated body, especially during fore-and-aft excitation. The nonlinearity of the body evident during single-axis vibration and multi-axis vibration, and the influence of backrests, should be taken into account when determining frequency weightings for human responses to vibration and when optimising the dynamics of seating.

Source : Qiu, Y. and Griffin, M. J. Biodynamic Response of the Seated Human Body to Single-axis and Dual-axis  Vibration: Effect of Backrest and Non-linearity. Industrial Health 2012, 50, 37–51.

http://www.jniosh.go.jp/en/indu_hel/pdf/IH_50_1_37.pdf

The assessment of the occupational noise exposure can be improved with the correct measurement strategies

This paper aims at analysing the impact resulting from the adoption of different strategies for assessing workers’ occupational noise exposure. Noise exposure assessment was made using the three strategies proposed in ISO 9612:2009, and computing the corresponding daily exposure level and associated uncertainty. The results obtained showed that the strategies recommended by that standard for each specific case represented the lowest time-consuming ones. The present work is a contribution towards improving the measurement procedure for the assessment of occupational daily noise exposure. The assessment of the occupational noise exposure is a complex and time consuming process, but it can be improved if the correct measurement strategies, for each case, are adopted. although the sample of workplaces of the present study is quite comprehensive, it is important to acknowledge that it was restricted to industrial environments, which is an important limitation. The possible distinct workplaces characteristics in non-industrial environments may affect some of the conclusions presented herein.

Source: Arezes, P.M. et al. Measurement strategies for occupational noise exposure assessment: A comparison study in different industrial environments. International Journal of Industrial Ergonomics 42 (2012) 172e177.

http://dx.doi.org/10.1016/j.ergon.2011.10.005

http://pdn.sciencedirect.com/science?_ob=MiamiImageURL&_cid=271473&_user=4494765&_pii=S0169814111001247&_check=y&_origin=article&_zone=toolbar&_coverDate=31-Jan-2012&view=c&originContentFamily=serial&wchp=dGLbVlB-zSkzV&md5=9a7ec1b475d608274120ddc55b64f95c/1-s2.0-S0169814111001247-main.pdf

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