The strategies and methods used for measurement and calibration during estimation and assessment of hearing ability and the risk to hearing were to be developed further and improved within the EU's "15HLT03 Ears II" project. Airborne ultrasound, the precise level of which cannot be measured by means of standard sound level meters, presents a particular challenge in this context. In addition, the levels of audible sound indicated during measurements with conventional sound level meters for noise measurements may be distorted where sources of ultrasound are present. The IFA was to develop a universal method for the measurement of airborne ultrasound at industrial workplaces.
A reference workplace employing a typical industrial ultrasound source was set up in the IFA's semi-anechoic chamber. An ultrasonic welding machine with a very wide range of adjustment served as the reference source. At this reference workplace, a range of existing and new methods for determining the sound exposure under different operating conditions were systematically investigated, and the measurement results from the respective methods compared. Particular attention was paid to the measurement of quantities stated in VDI 3766, the applicable standard for the measurement of audible sound in the presence of ultrasound. This enabled essential elements of a robust measurement method with known uncertainty to be determined for unoccupied workplaces. The measurement strategy resulting from the development was checked by means of field measurements at industrial workplaces, and developed further. Feedback on the measurement strategy was also obtained from a number of the German Social Accident Insurance Institutions and the SUVA. Owing to the short wavelengths of airborne ultrasound, the workers themselves may influence the acoustic field and the quantities to be measured. To permit quantitative assessment of these influences by workers, a study was conducted involving 20 test persons. All measurements were performed by a measurement system calibrated up to 100 kHz during the project.
The measurement methods currently used for determining audible sound exposure (ISO 9612) are not applicable to the determination of ultrasound exposure. These methods do not take the particular properties of airborne ultrasound fields into account. These properties are, in particular, strong spatial inhomogeneities, which may lead to changes in the sound pressure level of over 30 dB at a distance of just a few centimetres. In addition, it was observed that the methods described in the VDI 3766 standard for determining the sound exposure in the presence of ultrasound are also unsuitable for determining the workplace exposure to ultrasound. Essential elements of a measurement strategy for airborne ultrasound exposure were developed in the project. A draft strategy was formulated for the performance of measurements at unoccupied workplaces. The influence of a person present at the workplace upon the measurement result cannot be estimated with sufficient precision at the present time, however. Further analyses of the recorded data are required for this purpose, in conjunction with the measurement results obtained by the project partners. Therefore, a final conclusion regarding the exposure of individual persons cannot be drawn as yet.
-cross sectoral-Type of hazard:
noise, measuring methodsDescription, key words:
EMPIR, airborne ultrasound at the workplace