Castelo Branco, N. Low Frequency Noise, A Major Risk Factor in Military Operations

Col. Nuno A.A. Castelo Branco, MD, Centre for Human Performance, Portugal

“It is not surprising the Low Frequency Noise (LFN), including infrasound, was investigated in order to develop weapons. LFN is an ubiquitous agent of disease, especially in the military. Our group urges physicians in charge of LFN-exposed personnel to establish and implement prevention and protections programs against exposure and the development of Vibro-Acoustic Disease (VAD). It will be worth the fight!”


Noise is a major risk factor in many military environments. Noise is treated as a pollutant that can cause hearing damage and speech interference within the various vehicles and manned-stations. Thus, when protection against noise becomes an issue, the audible frequency bands (which coincide with those where speech occurs) are the focus of regulation and minimization.

Protection against noise is thus focused on these higher frequencies (>500 Hz), while the bands of lower frequencies (<500 Hz) are neglected, and non-audible bands, infrasound (<20Hz) are ignored. This decades-old policy is based on an erroneous assumption: “Noise only affects the ear.” This assumption pervades standard noise assessment procedures, the most blatant example of which is the use of the A-weighting system. This filtering system imitates human hearing, i.e., it de-emphasises the lower frequencies and, naturally, ignores the non-audible infrasonic bands of acoustic phenomena.

In effect, when an acoustic environment is described merely in terms of dB(A), only the acoustic phenomena that casn be perceived by the human auditory system is being evaluated. The acoustic environment may have significant components within the lower frequency bands including the infrasonic range, and yet the acoustic energy contained within these bands is not taken into account. Why? Because they are not a major contributor to hearing impairment and speech interference.

On the basis of our 20 years of research on the effects of low frequency noise (LFN – <500 Hz including infrasound), our team has learnt to regard LFN as an agent of disease (not just a pollutant), and to search for objective clinical indicators of LFN-exposure. LFN impinges upon an individual and it is irrelevant whether or not such acoustic phenomena is heard, or even perceived by the individual. X-rays are a perfect analogy: merely at a different frequency of electromagnetic radiation (or light), x-rays are not seen or perceived by the individual. Yet undue exposure to x-rays is a well-known health hazard. We propose the LFN be treated as x-rays, and thus human perception, i.e., annoyance, loudness, etc, are given the import of subjective measures.

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