Evaluation of the exposure risk to ultrasound emitted by ultrasonic cleaner machines: a case study.
Authors: Fabio Lo Castro, Sergio Iarossi, Massimiliano De Luca
Abstract: This paper presents a study on the ultrasonic emissions of some ultrasonic washing machines for both industrial and domestic use, which are now increasingly widespread, and their evaluation in compliance with current regulations. Since no threshold values or exposure limits for ultrasound are defined in the Italian and European legislation, criteria that are valid in other European and non-European countries among the most stringent have been adopted for the evaluation.For the evaluation, a methodology has been developed in the context of the collaboration between Eni - CNR. As a case study, an analysis of various ultrasonic washers machines of different sizes and power will be presented.MethodIn this study, 6 ultrasonic cleaner machines of different models and brands were examined. For each of them, it was measured the equivalent sound level not weighted in the ultrasonic bands and the peak level, Lpeak, at the receiver, close the operator at the ears height, generally in front of the device standing at 0.5 m from it. The instrumentation used for the measurements includes a 204 kHz acquisition card, and a class I microphone with a band up to 70 kHz, all certified as a class I sound level meter.Results and discussionFor each ultrasonic cleaner, the ultrasonic level was measured for each 1/3 octave band from 20 kHz to 80 kHz. The uncertainty level was 2.8 dB for the equivalent level and 2.4 dB for the peak level. The presence of the lid, depending on the model, performs several main functions: quickly raise the temperature inside the tank, prevent the lowering of the solution due to evaporation, and protect from any splashes during operation.Some models, even if was covered by the lids, exceeded the exposure limits established by us for the evaluation, and will be described in the paper. It should be noted that the peak level, Lpeak, was never exceeded. The evaluation criterion we have chosen is one of the most restrictive criteria, chosen to safeguard the worker as much as possible. Although the criterion is stringent, it is possible to find simple and economical solutions to be implemented in case of exceeding the limit.ConclusionThe study has shown that most of the devices if the tank is shielded, with a screen or simply the lid, they fall into the class of absence of risk. Otherwise, it is possible to reduce the exposure time or increase the distance spent near the washing machine to reduce the risk.
Keywords: Ultrasound, risk, exposition, cleaner machines
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