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Conducting noise surveys in today's mobile work environment |
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Written by Casella
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The industrial environment has changed drastically in recent decades with an increased level of mechanization within the workplace. This has given rise to many changes to employees' work patterns and has added new challenges to conducting noise surveys. A production line employee once would stay in a single place for the duration of a working shift. This lack of mobility made monitoring the employee's noise exposure a simple affair requiring only a traditional hand-held sound level meter. However, with the advent in automated production lines, employees may now supervise several machines during a single shift, moving from one workstation to the next, all of which having different noise exposures.
Sound Level Meters
In the past the only way to monitor precisely an employee's exposure to noise was using a sound-level meter. A sound-level meter is a hand-held device that allows a technician to capture measurements by pointing at the noise source from approximately the operator's ear. By repeating this exercise for all the operations an employee performs during a day, the technician can calculate daily exposure. On the other hand, where it is difficult to get close to employees with a sound-level meter or when workers are exposed to many different noise levels, a sound level meter falls short. Using a meter in these instances involves measuring noise levels at each workstation, charting how long the worker stays at each location, and then calculating the overall exposure. This approach simply isn't practical.
Dosimeters
A better solution to multiple location measurements is the noise dosimeter. A dosimeter is made up of a microphone, a cable and a small instrument that records and computes noise exposures. The microphone is clipped onto an employee's shirt or jacket and its cable is then passed under the clothing to the unit itself, which is small enough to be placed in a pocket or attached to a belt. At the beginning of a work shift the dosimeter is started. It will run continuously until the end of the working day. Once complete, the entire work shift's noise exposure can be directly read from the instrument or downloaded to a PC without the need for time-consuming calculations. Dosimeters log the noise data so that a time history of each unique noise can be viewed. Armed with this information the technician can immediately analyze when and where dangerous noise exposures occur. It also educates the plant manager to which operations require added ear protection for employees to reduce noise exposure.
Dosimeters worn by an employee for a complete working shift will measure the noise dose in full, so there is no need to make extra calculations to arrive at a full measure of exposure. However, if you need to make several measurements of different employees in the same day, a dosimeter can be moved from employee to employee, as long as the measurements taken for each are representative of a working day. Most dosimeters will project the noise dose forward to the standard 8 hours, so no calculations are needed.
With innovations in digital technology, noise dosimeters have become more compact and intrusive. So-called "badge" dosimeters are small and light enough to be worn on the shoulder, eliminating the need for microphone cables. Not only does the lack of cables make badge dosimeters safer to wear, but technicians will find employees to be less resistant to wearing one. Due to the small size of badge type products, it is also possible to mount them in more innovative ways, such as on a hard hat.
One word of caution: It is important to use a windshield in any sound level measurements, even when indoors. They provide protection from dust settling on the microphone which can compromise accuracy.
Standards and Accuracy
Noise dosimeters are manufactured to international standard IEC 61252. "Type 2" is the required accuracy for workplace regulations.
Before a dosimeter is used, regulations stipulate that it be checked with a field calibrator. It is also best practice to run the calibration test after an extended period of field measurements to check that there has been no significant drift. Both the dosimeter and the acoustic calibrator should be returned to the manufacturer for a true calibration every two years. A true calibration, performed by a calibration laboratory, consists of multiple tests including checking measurements across all frequencies and levels to ensure that the dosimeter still meets the requirements of IEC 61652.
Importance of Software
Modern dosimeters measure the essential parameters for workplace noise regulations including daily exposures and peak levels. However, it is important that this data be easily accessible and understandable, even to those employees unfamiliar with acoustic terminology. Professional-grade software allows the technicians to store data formatted by person or place for fast, accurate and easy-to-read analysis. Also, the software should allow final data to be moved into other reports with all the required data for workplace noise regulations, including the average and peak time history.
Conclusion
Noise dosimeters are crucial in monitoring today's highly mobile workers. Dosimeters provide valuable information by using the logged time history data on when and where the majority of noise exposure has taken place. This allows the implementation of noise control in the right place at the right time, which is the end goal of any noise survey.
For more information, visit www.casellausa.com.
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