2013-11-01 12:00 - Messages

Retrofit anti-vibration devices

A study of their effectiveness and influence on hand-arm vibration exposure
This project set out to try to determine what benefits, if any, could be gained in terms of reducing vibration exposure by retrofitting different types of anti-vibration device to different hand-held machines. Four types of device were selected for laboratory investigation: anti-vibration handles, spring balances/tensioners, a vibration reducing flange and chisel sleeves.
The results from all the different devices used in this project, with the exception of the chisel sleeves, demonstrated that an end user cannot be confident that their chosen retrofit device will in fact reduce vibration to the user and in turn reduce exposure. Indeed, the exact opposite may be true. Advice to end users should emphasise the need to speak to their suppliers to determine what, if any, retrofit devices are suitable for their particular equipment.

Source : http://www.hse.gov.uk/research/rrhtm/rr990.htm

Modeling acoustic propagation in a compartment fire

Firefighters unable to move and in need of rescue use an audible alarm to signal for help. Rescue teams can then follow this sound to the firefighter. This alarm is governed by NFPA 1982 : Standard on Personal Alert Safety System (PASS). Introduced in 1983, the PASS has saved many firefighter lives. However, a number of incidents have occurred where the PASS is less effective. There have been incidents where the PASS was heard sporadically on the fireground, or where localization of the alarm was difficult, leading to injury and loss of life. We hypothesized that the temperature field created by the fire is distorting the sound, making it difficult to recognize and localize. At ICA 2013, the authors presented experimental results showing changes in the room acoustic transfer function as the fire evolved. This paper will present efforts at modeling these effects. Using a combination of computational fluid dynamics and wave models, a comprehensive model will be presented capable of modeling sound propagation in the firefighting environment. The goal of this work is to develop a PASS signal more robust against distortion by the fire, and better able to serve the firefighting community.

Source : Abbasi MZ, Wilson PS, Ezekoye OA. J. Acoust. Soc. Am. 2013; 134(5): 4218.

Risk factors for hearing loss across occupations

A survey in Norway has investigated the link between a worker's job and the possible risk of hearing loss. While occupation was a factor in 2%–3% of the variance in hearing loss among men aged 45, it was of significance for less than 1% of women and young men. The most serious hearing problems in men were found among woodworkers, miners, electrical power line workers and cable jointers, carpenters, seamen and mechanics. Among women, there were only a few occupational groups indicating hearing problems.

Source : http://www.eurofound.europa.eu/ewco/2013/09/NO1309019I.htm

The effect of firefighter personal protective equipment on auditory thresholds

Communication on a fire scene is essential to the safety of firefighters. Not only to be able to hear and understand radio chatter, but also alarm signals used on the fireground. One such alarm is the Personal Alert Safety System (PASS) device. This device is used to help locate a downed firefighter. One part of this complex problem is the effect of the protective equipment (helmet, eye protection, hood, coat) on hearing. Previous findings have shown the effect of this protective equipment on head related transfer functions using a KEMAR. [Suits et al. (2013, June). Paper presented at the International Congress on Acoustics, Montreal, Canada] The physical acoustic measurements showed a change in the signal that would reach the tympanic membrane. To relate the findings of the physical measurements to human reactions, the change in auditory threshold caused by wearing the personal protective equipment was measured. The changes seen in the physical acoustics measurements caused the auditory threshold of the subjects to increase at higher frequencies. The measured increases at 3000 Hz, 4000 Hz, and with an example PASS signal were between 5 and 10 dB.

Source : Suits JI, Champlin CA, Wilson PS, Ezekoye OA. J. Acoust. Soc. Am. 2013; 134(5): 4228.

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