Ultrasound generates both audible and inaudible noises. A hissing working noise is typically generated with fluids.
Depending on intensity, possible effects on health are:
subjective - pain, dizziness, and
objective - impairment of hearing.
In order to assess noise situations in a practical manner, the measurement of noise levels is applied with a rating. Instead of the customary A-rating, which produces considerable measurement errors in the presence of ultrasound, ultrasound
uses the AU-rating. It takes into consideration the sensitivity of the human ear to airborne noise in the presence of ultrasound frequencies.
Comments regarding the rating:
Sound level meters, which use the evaluation curve A are not suited for noise measurement in the presence of ultrasound, since their built-in fi lters are only normed for noise levels up to 12 kHz. Higher ultrasound operating frequencies starting at 20 KHz may therefore produce false, considerably higher or even lower readings. For this purpose, an expansion of the A curve above 12 kHz – the U fi lter curve – was adopted by the IEC as an international norm.Combined with the A curve, this AU-rating was introduced and defi ned in the EN 61012 (IEC 1012). The AU level rating is based on comprehensive measurements of auditory threshold curves with 8 kHz 1/3-octave center frequencies, and thus makes possible a proper, broad assessment of the noise
In order to pre-assess a noise situation, a noise level measurement with AU rating, for example, would make sense in the direct sound fi eld over the ultrasound source. The adjacent test arrays for ultrasonic baths is proposed for a realistic personal simulation and reproducibility of measurements (similar to homogenizers).
Two measurements are conducted:
I. with a distance of 1 m over the bath surface, the microphone axis is aimed over the noise
II. at the same distance; microphone axis aimed at an angle below 45°.
By way of example, the following dB(AU) values were measured in our manufacturing facilities for the baths with lid listed below:
|Bath||RK 31||RK 100 H||RK 255 H||RK 514 BH||RK 1028 CH|
Any noise produced is heavily dependent on set-up, installation and process technology. For this reason, it is not possibleto draw any general conclusions regarding noise levels produced at the installation site.
A noise level that is too high may have diverse origins that can generally be easily addressed:
- Adjust the position of the object being treated, never lay objects on the tank bottom (tank baths).
- Adjust the immersion depth of the object being treated (tank baths) or of the probe (homogenizers)
- Adjust the fi ll level of the bath fl uid, place the lid on during operation (tank baths).
It is generally recommended that suitable hearing protection be worn, or that appropriate sound proof boxes be used, in
the event of constant activity within a periphery of 2 m:
- For ultrasonic baths,
- For ultrasonic homogenizers
If there is no improvement, please contact the manufacturer.
Basic specifi cations for the reduction of noise hazards, as well as limit values can be regulated in each national
specifi cations and must be observed accordingly.
According to recent studies, the use of a lid to hinder aerosols from active ultrasonic baths is no longer necessary. “Current results show that when operating an ultrasonic bath without a lid, service personnel are not at risk of inhaling microorganisms that may be transported from the ultrasonic bath into the air.“ 1 and “When treating medical instruments, the water temperature in the ultrasonic bath generally does not exceed 40 °C, however, so the risk of dispersion of germs through the formation of aerosols in the ambient air is to be considered exceedingly low.“ 2.
In order to prevent possible health risks through direct contact with the ultrasound source, it is important that during operation you do not
• make contact with the tank (tank baths),
• make contact with the ultrasound bath (tank baths),
• touch the probe (homogenizers).
In the event of high ultrasonic power, tissue or bone skin may be damaged based on the penetration depth, even during a short exposure time.
Instructions for special groups of persons
The ultrasound energy that is radiated through the air does not present a health risk to the foetus. This also applies to pregnant women who linger in the area where ultrasound baths or homogenizers are found.
Persons who wear medical implants (implants with electrical or electromotorized functions)
Our ultrasonic baths and homogenizers conform to the European EMC and low-voltage directive underlying the CEmark, through adherence to valid norms and regulations for the protection of electromagnetic fi elds. Therefor it can be assumed that the electromagnetic radiation that is emanated by ultrasonic baths and homogenizers is harmless to humans.
An ultimately binding assessment and conclusion regarding the hazard to persons with or without implants, can only be made at the actual workplace and in consultation with the manufacturer of the implant.
In case of doubt, information is to be obligatorily procured for wearers of implants, e.g. of pacemakers, regarding theallowable electromagnetic fi eld strength exposure level, from the implant manufacturer.
1 B. Fiedler*, J. Steinke: Investigation of ultrasound-induced microbial emission into the room air from contaminated ultrasonic baths; Zentralsterillisation; volume 5; 2013;
p. 341 ff.
2 L. Riik*, R. R. Radandt, R. Jung, W. Vollmann, J. Landskron: Physical-technical investigations into ultrasound-induced aerosol formation from ultrasonic baths used in the
medical setting; Zentralsterillisation; volume 6; 2013; p. 426 ff.