Measurements according to ISO 9612
The occupational noise measurement is based on assessment of daily noise exposure level (LEX, 8h) defined by ISO 1999. The LEX,8h is basically a 8-hours extrapolation of LAeq measured over the working hours. The Directive set up limits for LEX, 8h: 87 dBA as the daily limit, 85 dBA as the upper action value and 80 dBA as the lower action value. Additionally the LCpeak should be measured which limits are accordingly 140, 137 and 135 dBC.
In practise many European countries follow techniques of ISO 9612 for occupational noise measurements. The ISO 9612 provides three measurement strategies: task-based, job-based and full-day measurement. The choice of strategy is done depending on the circumstances in the factory.
The ISO 9612 methodology uses three measurement strategies. The selection of the measurement strategy is based on the work analysis, such as tasks, noise sources, work pattern and breaks. In practise the task-based strategy is used for simple tasks or at fixed workstations. The second strategy, job-based, is recommended when noise exposure of any worker within a group of workers is representative to the group. As a job is a group of tasks performed by one worker, job-based measurement does not require a detailed breaking down of the work activity into tasks, therefore is less time consuming. The third, full-day measurement strategy is used when the workers are mobile, and their pattern of work is unpredictable or complex. In fact the third strategy is applicable to the most work patterns but is the most time consuming strategy.
The collected measurement results are basis for determination of A-weighted noise exposure level (LEX, 8h) which is then compared to the limits. The ISO 9612 requires the data analysis to verify all unwanted noise sources, such as mechanical impacts on microphone, windblows, or artefacts.
Personal sound exposure meter integrated with the microphone, meeting specification of IEC61252, often called as “noise dose meter” or “noise dosimeter”
Sound Level Meter
Sound level meters meeting requirements for Class 1 or Class 2 of IEC 61672-1. Class 1 are recommended especially in low temperatures or when noise is dominated by high frequencies.
PC software for measurement data post-processing and reporting according to ISO 9612 procedures.
The sound calibrator meeting requirements of IEC 60942:2003, class 1, providing one or more frequencies within the rage of interest.
Noise can be measured using a sound level meter or a noise dosimeter. A sound level meter measures sound level at a single point in time, which is useful when sound is steady‑state with little variation in level. Sound level meters are inexpensive, widely available, and relatively simple to use. When sound exposures vary in level and duration it’s difficult to accurately estimate exposure using a sound level meter, and a noise dosimeter should be used instead.
A noise dosimeter measures sound levels continuously over time and integrates them into a single value, the noise dose. A dosimeter provides a more accurate estimate of noise exposure when sound levels fluctuate and/or exposure durations vary, and can alert the user in real time to the need for hearing protection based on the accumulated noise dose. Noise dosimeters are easy to operate and can be used for a wide variety of applications.
The noise dosimeter, also referred as “personal sound exposure meter” is basically a wearable sound level meter of a class 2 accuracy. The personal noise dosimeter may be worn on the shoulder, collar, or other location close to the ear.
The ISO 9612 recognizes the use of hand-held sound level meters as well as personal noise dosimeters. The preferred instrument is noise dosimeter, meeting requirements of IEC 61652 and IEC 61672-1, class 2. In case of measurements in low temperatures or when noise is dominated by high frequencies the class 1 instruments are recommended.
Measurement instrumentation should be calibrated before and after each series of measurement and additionally should be verified in the accredited laboratory at leas once every 2 years.
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