Measurements of Infrasound Signatures From Grenade Blast During Training.

Introduction: Military personnel during training and military operations are exposed to a large number of repeated exposures to low-level blast overpressure from a variety of sources. These exposures rarely produce a concussion, but anecdotal evidence from soldiers indicates that it can still cause transient neurological effects. Impulsive acoustic sources, such as the ones encountered during military training, are characterized by a broadband energy distribution with resulting pressure measurements that exhibit frequency components well within the infrasound range. This infrasound can couple directly with the human body and in this way alter or influence physiological processes up to inducing concussion-like symptoms.

Materials And Methods: This study explores the presence of infrasound energy in measured acoustic signals collected during grenade training at Ft. Benning, GA. Acoustic data from traditional microphones and specialized infrasound microphones were collected during one training session and time and time-frequency analysis was performed to highlight the frequency content of the signals.

Results: The analysis of the collected measurements indicates peak SPLs between 140 and 160 dB during explosions corresponding to the shockwave. Also, high-intensity infrasound was observed during grenade explosions with significant energy in the infrasound range and in particular below 3 Hz. This energy appears in the form of three distinct tones at frequencies of 1.987, 2.296, and 2.528 Hz that are present only for the duration of the blast wave.

Conclusions: The results presented in this article suggest that reported symptoms from military personnel exposed to repeated low-level blast may also be because of acoustic loading. Therefore, to take into account these findings, future studies aimed at characterizing the effects of repeated low-level blast exposure should consider including acoustic measurements in their investigations.