Page 49 - Occupational Health & Safety, October 2018

main of the hand-held sound level meter was the ability to perform octave band fre- quency analysis of the noise to help select the most appropriate noise control meth- ods to reduce the high levels, or at least to assist in the correct prescription of the best hearing protectors as a short-term solution.
This usually involved going back to the worker after downloading results and see- ing when it was noisy, and then trying to return to the same place at the same time in the day and discover what was happen- ing. Some newer shoulder-mounted noise dosimeters feature optional octave band analysis all the time during the recording of the noise exposure results. This has the ex- tra advantage of not needing to go back and repeat measurements when it may not be possible to know for sure when and where they occurred. It also means the true noise sources are measured at the same time as the dose percentage and the average noise levels are being collected. This leads to much more useful and accurate determi- nations of the likely harmful exposure fre- quencies and a more accurate choice of the right hearing protectors for the worker.
Vibration Sensors and
Other Improvements
Of course, there is always the possibility that the microphone may get knocked dur- ing the measurements, leading to errone- ous results for the true peak level and possi- bly overestimating the time average result, as well. Some modern dosimeters feature a self-monitoring vibration sensor that marks samples during the run when the dosimeter is knocked or bumped acciden- tally (or deliberately), and these results can be identified in the software and removed after downloading.
The vibration sensor in the dosimeter also serves another useful purpose, that of monitoring when the instrument is not be- ing worn. This helps to alert when the op- erator may have taken it off and set it down on a stationary surface when going to the re- stroom, perhaps. The dosimeters can detect when the instrument is being worn even if the operator is just sitting at a bench work- ing normally so they can provide very useful information to the IH looking to be sure that nothing out of the ordinary has occurred.
In the beginning of personal noise do- simetry measurements the available instru- ments simply provided an overall noise dose percentage result based on one of
the protocols specified by the regulatory bodies around the world. Gradually more results were included to better represent the measurement to give more insight into what had occurred, including: peak levels, maximum levels, time average levels, and normalized time weighted average levels. Measurements with different protocols re- quired repeats of the measurement to gain the right information about a worker’s ex- posure patterns and could take two or three days to collect.
Current noise dosimeters feature mul- tiple “virtual noise dosimeters” inside a single instrument by carefully splitting the acoustic path into two or three or more separate profiles configurable by the user. This way, a single measurement can now produce results calculated by the different required methods, OSHA, ACGIH, ISO, or even a user’s own in-house protocol. One measurement saves time and effort by col- lecting all results in parallel.
Newer dosimeters also can feature Bluetooth communications for use with a dedicated app on a smartphone or tablet to review the accumulated noise exposure
any time during the shift without having to interfere with the worker. This is a great practical advantage and enables the IH to see what the exposure levels are so far with- out getting in the way of the worker.
Conclusion
Modern noise dosimeters are small, light- weight, feature multiple virtual instru- ments, and have many useful options to better describe the complete hazard. Ad- vancements in technology have provided ample memory and low power consump- tion run times for a full week of daily mea- surements using high-capacity recharge- able batteries. With all of these advantages, the question sometimes arises, where do we go next to protect our workforce even better? What will the future hold for the next generation of noise dosimeters? Only time will tell.
Bob Selwyn is the North American Sales Manager for Svantek Sound and Vibration Products, Sensidyne LP. He has more than 40 years of experience in the field of IH mea- surements.
www.ohsonline.com
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