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11 PROTECTION AGAINST INFRASOUND AND

ULTRASOUND

11.1 Ultrasound

The sources of the ultrasonic vibrations work in the frequency range of 16 to
80 kHz (Figure 11.1).
Ultrasound can be generated by a variety of industrial processes: cleaning,
drilling, welding plastics, mixing. Their influence is observed at a distance of 25–50
m.

Figure 11.1 – Ultrasonic range diagram

Ultrasound causes the functional disturbances of the nervous system,
headache, change of blood pressure and blood properties, the loss of the auditory
sensitiveness and fatigue.
Admissible levels (AL) of the ultrasound:
1) Al in the places of contact of the parts of the body of the operator with the
working machine parts must not exceed 110 dB.
2) In the case of the total effect of the ultrasound:
 from 1 to 4 hours during one shift the normative value can be increased
by 6 dB;
 under its effect from 0.25 hour to 1 hour – by 12 dB;

 from 5 to 15 min – by 18 dB;
 from 1 to 5 min – by 24 dB.

Protective methods from the ultrasound:
 sound-proofing;
 protective shields (shelter materials are steel, duralumin, acrylic resin,
cloth laminate added to the acoustical absorbents);

 the use of the booths of the remote control;
 vibration isolation (vibration isolation coverage, rubber mittens, carpets).

11.2 Infrasound

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