Low Frequency Noise: A Major Risk Factor in Military Operations 

Paper presented at the NATO Research and Technology Organisation’s Applied Vehicle Technology Symposium on “Ageing Mechanisms and Control: Part A – Developments in Computational Aero- and Hydro-Acoustics”,
held in Manchester, U.K., 8-11 October 2001, and published in RTO-MP-079(I).

Background. Noise is a major factor in many military environments. Usually the concern is with the higher frequency bands (>500 Hz) that cause hearing damage or interfere with speech. Protection against noise is thus focused on these higher frequencies, while the bands of lower frequencies (<500 Hz) are neglected, and non-audible bands, infrasound (<20 Hz) are ignored. In reality, long-term exposure to low frequency noise (<500 Hz, including infrasound) (LFN) can be quite detrimental to one's health. LFN-Induced Pathology. The disorders associated with occupational exposure to LFN have been described for aeronautical technicians and pilots. Diagnostic tools and methodologies for monitoring and controlling the development of LFN-induced pathology, have already been outlined. Immediate effects of LFN-exposure can include a) decreased capacity for cognitive functions, which implies a decline in performance, the consequences of which can be minor to devastating; b) sudden onset of acute respiratory problems, neurological disturbances, and mood alterations, such as, rage reactions. Cumulative effects of LFN-exposure can include triggering of early aging processes, and the development of vibroacoustic disease in susceptible (70%) individuals. Early compulsory retirement is a frequent situation.

Costs. Almost all military equipment require training programs for the operator. Long-term exposure to LFN can severely decrease the cost-return ratio for these operators, i.e., investment in training programs has little or no return. Accident/incidents can also damage the equipment itself, potentially jeopardizing missions. Waste of ammunition and other resources is another consequence of unmonitored LFN-exposed operators. The cost of ignoring LFN as an agent of disease is ultimately more expensive than the prevention, protection and, above all, selection of personnel for noise-environment positions.

Col. Nuno A.A. Castelo Branco, MD (PoAF, res.)
Center for Human Performance
Alverca, Portugal

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