Health hazard

Ultrasound and health hazards #

Noise

Ultrasound produces inaudible and audible noises. Typical is the hissing working noise that occurs with liquids. Possible health effects depending on the intensity can be:
subjective - pain, dizziness and
objective - impairment of hearing.

For the practical assessment of noise situations, sound pressure level measurement with weighting is used. Instead of the usual A-weighting, which produces considerable measurement errors in the presence of ultrasound, the AU-weighting is used for ultrasound. This takes into account the sensitivity of the human ear to airborne sound at ultrasonic frequencies.

Explanations on the evaluation:
Sound level meters using the A-weighting curve are unsuitable for noise measurement in the presence of ultrasound, as the built-in filters are only standardised for sound pressure levels up to a frequency of 12 kHz. Higher ultrasonic operating frequencies of 20 kHz and above can therefore lead to incorrect, significantly higher or even lower measurement results. For this purpose, the IEC has adopted an extension of the A-weighting curve above 12 kHz - the filter curve U - as an international standard.
Combined with the A-assessment, the so-called AU-assessment was introduced, defined in DIN EN 61012.^/1. The AU level assessment is based on extensive measurements of hearing threshold curves with 8 kHz third-octave centre frequencies and thus enables a proper broadband assessment of the sound level.

For a preliminary assessment of the noise situation, e.g. a sound level measurement with AU assessment in the direct sound field above the ultrasonic source is useful.
Based on the VDI guideline VDI 3766^/2BANDELIN has defined the measuring set-up for ultrasonic baths shown above (homogenisers similar) for person-related simulation and reproducibility of the measurements. Two measurements are carried out:
I. at a distance of 1 m above the surface of the bath; the microphone axis is directed towards the sound source.
II. with equal distance; microphone axis at an angle of 45°.

In our production facilities, AU-weighted sound pressure levels are measured for the ultrasonic baths with lid and basket.
The sound pressure level for all baths is
L_/pAU(t) < 80 dB
and is thus below the recommended guideline value of the VDI 3766 guideline.
The noise level is strongly dependent on the construction, the installation situation and the use. Therefore, no general statement can be made about the sound pressure level at the installation site.

An excessively high sound pressure level can have various causes, most of which can be easily remedied:
- Changing the position of the sonication object, never place objects on the floor of the tub
(baths).
- Changing the immersion depth of the sound reinforcement object (baths) or the
Sonotrode (homogenisers)
- Changing the filling level of the bath liquid, operation with lid (tub baths).
In general, it is recommended to wear suitable hearing protection or to use appropriate noise protection boxes when working continuously within a radius of 2 m:
- For ultrasonic baths, e.g. under:
https://www.sonation.com/
- For ultrasonic homogenisers, e.g. under:
https://bandelin.com/
If there is no improvement, please contact the manufacturer.
Notes:
(1) Basic provisions for the protection of employees from hazards due to noise and vibrations are regulated in the Noise and Vibration Occupational Health and Safety Ordinance (Lärm- und Vibrations-Arbeitsschutzverordnung - ArbSchV) and must be observed accordingly.
2. the DIN 45645-2 standard^/3 is not suitable for an assessment of ultrasound exposure in the workplace.

Aerosol

In the TRBA 250 ^/4Chapters 4.2.3 and 5.4.6 state that when instruments are cleaned in the ultrasonic bath, it must be covered or suctioned off.This no longer seems justified according to more recent investigations. "According to the available results, the operation of an ultrasonic bath without a cover does not pose a risk to the operating personnel due to inhalation of
Microorganisms transported from the ultrasonic bath into the air." ^/5 and "The usual procedure for reprocessing medical instruments in the
ultrasonic bath, however, a water temperature of 40 °C is not exceeded, so that the risk of germ dispersion through aerosol formation into the room air can be assumed to be extremely low." ^/6.

Direct contact

In order to exclude a possible health hazard due to direct contact with the ultrasonic source, it is pointed out that during operation
- not to touch the tub (tub baths),
- not to reach into the ultrasonic bath (tub baths),
- not to touch the horn (homogenisers).

At high ultrasound powers, damage to the tissue or periosteum can occur even after a relatively short exposure time due to the penetration depth.

Notes for special groups of people

Pregnant

The ultrasound energy radiated via the air is not hazardous to the health of the foetus. This also applies to pregnant women who are in the area of ultrasound baths or homogenisers.

Persons with physical aids
(Implants with electric or electromotive function)

Our ultrasonic baths and homogenisers fulfil the conformity to the European EMC and Low Voltage Directive on which the CE mark is based by complying with valid standards and regulations for protection against electromagnetic fields. In particular, through safe compliance with field strength impact levels
according to the German Social Accident Insurance Institution regulation DGUV Vorschrift 15, it can be assumed that the electromagnetic radiation emitted by the ultrasonic baths and homogenisers is harmless to humans.
An ultimately binding measurement and statement on the risk to persons without or with implants in accordance with DGUV Regulation 15 can only be made at the specific place of work and in consultation with the manufacturer of the implant. In case of doubt, information on permissible electromagnetic field strength exposure levels for wearers of implants, e.g. pacemakers, must be obtained from the respective implant manufacturer.
All information is based on the current state of our knowledge; however, it does not constitute a guarantee of product characteristics and does not establish a contractual legal relationship with BANDELIN.

^/1 DIN EN 61012; 1998-09: Filters for the measurement of audible sound in the presence of ultrasound (IEC 61012:1990) German version EN 61012:1998

^/2 VDI 3766; 2012-09: Ultrasound - Workplace - Measurement, evaluation, assessment and reduction

^/3 DIN 45645-2; 2012-09: Determination of rating levels from measurements - Part 2: Determination of the rating level at the workplace for activities below the level range of hearing risk

^/4 TRBA 250; 2014-03: Biological agents in the health care and welfare sector

^/5 B. Fiedler*, J. Steinke: Untersuchungen zur ultraschall-induzierten Keimemission in die Raumluft durch kontaminierte Ultraschallbäder; Zentralsterillisation; Heft 5; 2013; S. 331 ff.

^/6 L. Riik*, R. R. Radandt, R. Jung, W. Vollmann, J. Landskron:
Physical-technical investigations on ultrasound-induced aerosol formation in ultrasonic baths used for medical purposes; Zentralsterillisation; Heft 6; 2013; S. 421 ff.