Awareness of the hearing damage risk posed by exposure to excessive noise levels in the workplace and elsewhere, plus the increase in successfully contested industrial deafness cases has led to improved ear protection for many workers in recent years.
However, further hidden dangers lurk in the airwaves, which the ear cannot detect but are just as real a threat as noise induced hearing loss is to health and safety.
Infrasonics are very low frequencies of between 2–16 Hz, which the human ear cannot pick up because they they are below the normal, frequency detection range of 16-20,000 Hz. The deeper a frequency, the higher the sound has to be amplified so it can be detected.
On a sliding scale of frequency to decibel amplification, in order for sound to be heard :
100 Hz requires 23 decibels.
20 Hz requires 70 decibels
4 Hz requires 120 decibels.
This means that we can be subjected to excessive noise levels in the lower frequencies without hearing the sound, which can result in hearing loss if the sounds are over the 85 decibel safety threshold level. The undetected sound waves of infrasonics can disturb the body’s natural frequencies to cause imbalance leading to nausea, restlessness, headaches and tinnitus, as with the known effects of sea sickness.
Infrasonics can be caused by the wind, air currents or other meteorological interferences. However, heavy industrial plant, machines, compressors or heavy vehicles can also cause the infrasonic waves. Infrasonics have long wave lengths and move very slowly. Consequently, they are most often revealed in open or in large halls and office spaces longer than 20 metres. Thus, people who are employed in industry or who work in large offices where there is a ventilation system are especially exposed to infrasonic waves.
Due to their long wavelength, protection is difficult as they penetrate at almost full strength. A door, wall or ear plugs are not effective protection, and special sound-absorbing ear defenders or a certain type of sound-absorbing surface are required.