Page 92 - 6848

Infrasound is a mechanical vibration of the resilient environment with a
frequency of 20 Hz and less.
Infrasound can be generated by natural events: thunder, winds, volcanic

activity, large waterfalls, the impact of ocean waves, earthquakes. Also, it can be
generated by man-made events: high powered aircraft, rocket propulsion systems,
explosions, sonic booms, bridge vibrations, ships, air compressors, washing
machines, air heating and cooling systems, automobiles, trucks, watercraft and rail
traffic.
The infrasound effect on a human at the level of 100–120 dB especially at 6–8
Hz frequency can cause:
 unpleasant feeling;
 hearing impairment;
 nausea;
 dizziness;

 disturbances of the vestibular apparatus.

At the upper end of the audio range, hearing sensitivity decreases at the rate of
approximately 100 dB/octave, compared to 10–20 dB/octave for low audio and
infrasonic frequencies. Most HPDs (hearing protection devices) provide relatively
good attenuation at high frequencies.
Ways of protection:
 reduction of the infrasound level in its origin;
 removal of the infrasound causes;
 medical prophylaxis;

 increase of the frequency of mechanism rotation;
 increase in construction inflexibility;
 mufflers installation.

Revision Questions

1) Protective methods from the ultrasound.
2) Ways of protection against infrasound.

4