2012-05-01 12:00 - Messages

An approach to the control system design of seat suspension systems for the active vibration attenuation

This paper presents an approach to the control system design of seat suspension systems for the active vibration attenuation. The paper presents the studies of the active vibration control strategy based on the reverse dynamics of force actuator and the primary controller. The multi-criteria optimization procedure is utilized in order to calculate the primary controller settings which subsequently define the vibro-isolation characteristics of active suspensions. As an example of the proposed control system design, the seat with a pneumatic suspension is investigated and its vibro-isolation properties are shaped by an appropriate selection of the controller settings.

Source : I. Maciejewski. Control system design of active seat suspensions. Journal of Sound and Vibration, Volume 331, Issue 6, 12 March 2012, Pages 1291-1309

http://www.sciencedirect.com/science/article/pii/S0022460X11008881

Davantage de salariés exposés au bruit dans un contexte de meilleur repérage des expositions

Au cours des quinze dernières années, la proportion de salariés exposés à des bruits supérieurs à 85 dB(A), toutes durées d’exposition confondues, s’est accrue, passant de 13 % en 1994 à 18 % en 2003 puis 20 % en 2010. Cette hausse concerne l’ensemble des catégories professionnelles mais est particulièrement marquée pour les ouvriers. Il est possible que cette évolution provienne en partie d’un meilleur repérage du bruit grâce à des campagnes de mesurage. En 2006, l’abaissement du seuil réglementaire à 80 dB(A) - seuil au-dessus duquel les salariés doivent faire l’objet d’une surveillance renforcée – a pu accroître le nombre de salariés plus particulièrement suivis par les médecins du travail du fait de leur exposition au bruit. La proportion de salariés lourdement exposés au bruit (supérieur à 85 dB pendant 20 heures ou plus par semaine) est restée stable autour de 6 % depuis 1994 mais la part des salariés lourdement exposés au bruit et ne disposant pas d’une protection auditive s’est réduite, passant de 2 % en 1994 à 1 % en 2010.

 

Source : SUMER- Charge mentale en hausse, contraintes physiques en baisse. Travail & Sécurité- Mai 2012.

 http://www.travail-et-securite.fr/archivests/archivests.nsf/(alldocparref)/TS728page14_1/$file/TS728page14.pdf?openelement

Voir aussi : 2012-023 - L’évolution des risques professionnels dans le secteur privé entre 1994 et 2010 : premiers résultats de l’enquête SUMER. Dares Analyses-Dares Indicateurs- 16 mars 2012

http://www.travail-emploi-sante.gouv.fr/etudes-recherche-statistiques-de,76/etudes-et-recherche,77/publications-dares,98/dares-analyses-dares-indicateurs,102/etudes-recherche-statistiques-de,76/etudes-et-recherche,77/publications-dares,98/dares-analyses-dares-indicateurs,102/2012-023-l-evolution-des-risques,14710.html

Use of vibratory tools increases more than five times the risk of developing CTS

A conservative definition of CTS employed to include nerve conduction abnormality with symptoms and/or signs showed that risk factors significantly associated with an increased risk of CTS among exposed workers were: vibration [odds ratio (OR) 5.40; 95% CI 3.14, 9.31], hand force (OR 4.23; 95% CI 1.53, 11.68) and repetition (OR 2.26; 95% CI 1.73, 2.94). Using National Institute for Occupational Health and Safety criteria for case definition, a significant positive association between CTS and hand force, repetition, use of vibratory tools and wrist posture was observed with approximate doubling of risk for all exposures. Thirty-seven studies from English-language literature met the inclusion criteria of this meta-analysis.

Source: Barcenilla, A. et al. Carpal tunnel syndrome and its relationship to occupation: a meta-analysis. Rheumatology (Oxford). 2012 Feb;51(2):250-61. Epub 2011 May 17.

http://www.ncbi.nlm.nih.gov/pubmed/21586523

Évaluation de l'exposition aux vibrations globales du corps chez les opérateurs de compacteurs de sol

L'exécution de travaux routiers et de compactage de sols se fait généralement à l'aide de compacteurs vibrants monocylindres (à rouleau compresseur). Or, ces engins exposent les opérateurs à des niveaux de vibrations globales du corps élevés, reconnues comme un facteur de risque du développement de lombalgies. Seules quelques études européennes ont jusqu'ici caractérisé leurs vibrations, lesquelles dépassent parfois la limite maximale d'exposition quotidienne. Cette activité consiste à évaluer et à caractériser l'exposition aux vibrations globales du corps des opérateurs de compacteurs monocylindres parmi les plus utilisés au Québec. En plus de préciser le risque pour leur santé, elle permettra de recommander des façons de diminuer l'exposition aux vibrations, notamment par l'utilisation de sièges à suspension. Les résultats de cette étude pourront guider les fabricants dans la sélection de tels moyens et pourraient aussi proposer d'autres moyens pour réduire les vibrations. Ultimement, alors qu'on anticipe une croissance des investissements dans les infrastructures, les compacteurs améliorés contribueront à préserver la santé des travailleurs ainsi qu'à améliorer leur productivité.

Source : http://www.irsst.qc.ca/-publication-irsst-evaluation-de-exposition-aux-vibrations-globales-du-corps-chez-les-operateurs-de-compacteurs-de-sol-r-735.html

Cardiovascular Risk in Rotogravure Industry

Objective: To verify whether the occupational hazards in the rotogravure industry can be associated with cardiovascular effects.
Methods: We evaluated cardiovascular parameters and audiometric tests and analyzed noise, solvents, and shift work in 44 exposed and 44 unexposed workers.
Results: Unlike unexposed workers, the rotogravure workers showed significant increase of mean systolic and diastolic blood pressure (BP) values (P = 0.019; P = 0.003), higher frequency of hypertension (P = 0.002) and electrocardiographic abnormalities (P = 0.0001), significant reduction or no variation of BP response to orthostatism (P = 0.0001), and association between high levels of noise and diastolic blood pressure (P = 0.0067). Subjects with hearing loss showed high frequency of hypertension and a reduction or no variation of BP response to orthostatism (both P = 0.05).
Conclusions: Data obtained suggest that these are the effects on the cardiovascular system of rotogravure workers who are exposed to noise.

Source : Sancini, Angela PhD; Tomei, Gianfranco PhD; Vitarelli, Antonio MPH; Caciari, Tiziana MD; Samperi, Ilaria MD; Pacchiarotti, Alessandro MD; Scala, Barbara MD; Schifano, Maria Pia MD; Scimitto, Lara MD; Fiaschetti, Maria MD; Cetica, Carlotta MD; Tomei, Francesco MPH; Ciarrocca, Manuela PhD. Journal of Occupational & Environmental Medicine: May 2012 - Volume 54 - Issue 5 - p 551–557.
http://dx.doi.org/10.1097/JOM.0b013e318247a42d

Whole body- vibration (WBV) levels remained just above ISO 2631-1 after being optimized for load-haul-dump (LHD) vehicles

Operators of load-haul-dump (LHD) vehicles are commonly exposed to wholebody- vibration (WBV) levels above ISO 2631-1 and EU Directive 2002/44/EC guidelines. Vibration exposure was lowest when the LHD was driven at the lowest speed, forward, over smooth terrain, with ride control on and the bucket loaded (0.20 m/s2). The A(8) decreased from 0.84 m/s2 when driving with ride control off, over mixed terrain using all gears, to 0.53 m/s2 when driving with ride control on and an optimized seat. The estimated daily exposure decreased but remained just above the ISO 2631-1 and EU Directive 2002/44/EC guidelines.

Source : Edger, T.R., Contratto, M.S., Dickey, J.P. Influence of Driving Speed, Terrain, Seat Performance and Ride Control on Predicted Health Risk Based on ISO 2631-1 and EU Directive 2002/44/EC. Low Frequency Noise, Vibration and Active Control, Vol. 30, Number 4/ December 2011.

http://dx.doi.org/10.1260/0263-0923.30.4.291

While awaiting the new EPA's labeling regulation, train users to fit protectors correctly

EPA's final rule regarding hearing protection labeling is still pending. The proposed rule changes the very heart of the Noise Reduction Rating (NRR). The new NRR will be a range that is reported from very different testing methods than the old (current) NRR. These proposed labels do provide more information for the consumer but might also lead to some confusion. Knowing what kind of hearing protectors are best for a given situation will help understand the information provided on the new labels. The proposed method for labeling hearing protector includes the obvious but often misunderstood concept that "The sound pressure level at the user's ears will depend upon the fit of the protector." The best way to use the time while we're awaiting the new regulation on labeling of hearing protectors is to train users to fit the protector correctly and to use fit testing to document the protection provided by a given hearing protector.

Source : Theresa Y. Schulz. HEARING PROTECTION: Hearing Conservation in 2012: Focus on NRR.Occupational Health & Safety. March 2012.

http://ohsonline.com/Articles/2012/03/01/Hearing-Conservation-in-2012.aspx

Dental personnel in Thailand are exposed to noise intensities lower than occupational exposure limits.

This cross-sectional study was performed in the Dental School of Prince of Songkla University to ascertain noise exposure of dentists, dental assistants, and laboratory technicians. The peaks of the noise spectrum of dental instruments were at 1,000, 4,000, and 8,000 Hz which depended on the type of instrument. Noise measurement in the personal hearing zone found that the laboratory technicians were exposed to the highest impulsive noise levels (137.1 dBC). The dentists and dental assistants who worked at a pedodontic clinic had the highest percent noise dose (4.60 ± 3.59%). In the working areas, the 8-hour time-weighted average of noise levels ranged between 49.7-58.1 dBA while the noisiest working area was the dental laboratory.

Source : Choosong, T. et al. Noise Exposure Assessment in a Dental School. Saf Health Work 2011 Dec;2(4):348-354.

http://dx.doi.org/10.5491/SHAW.2011.2.4.348

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