Acute Hearing Deficits associated with Weapons Exposure in Section 734 Blast Overpressure Study (BOS).

INTRODUCTION: This prospective, multi-site, observational study describes ongoing efforts in support of the Fiscal Year 2018 National Defense Authorization Act (NDAA) Section 734 Blast Overpressure Study (BOS) to identify the acute effects impulse and blast exposure have on hearing abilities of the Warfighter in various military training environments. MATERIALS AND METHODS: Hearing thresholds, a binaural tone detection task, and auditory symptoms were collected before and immediately following weapons exposure across nine military training environments from January 2020 to October 2022. An additional 25 non-exposed control participants also completed the behavioral test battery. A boothless audiometer was used to measure hearing ability in the field. Sound level meters were attached on-body to record the exposure environment throughout training. RESULTS: Mean threshold change for the blast-exposed group was worse than the control group. Of the 188 blast-exposed participants, 23 experienced a temporary threshold shift (TTS) acutely after exposure. A decrease in binaural tone detection performance and increased symptom severity was found when comparing blast-exposed participants with a TTS versus those without a significant change in hearing. A complex but consistent relationship between measured exposure level (LAeq8hr) and the magnitude of the resulting TTS is suggested in the available data. CONCLUSIONS: Recent discussions on Section 734 studies examining the effects of repetitive blast exposure have indicated that hearing-related issues were a critical problem that needed additional research. Study outcomes provide highly repeatable results across various weapons systems with hazardous blast exposure. This standardized set of hearing assessment tools for evaluating acute effects of noise under field conditions has been critically important in improving our understanding of TTS in prospective human subject research.

An Exploratory Comparison of Water-Tamped and -Untamped Explosive Breaches: Practical Applications for the Tactical Community via a Pilot Study.

BACKGROUND: Tamping explosive charges used by breachers is an increasingly common technique. The ability to increase the directional effectiveness of the charge used, combined with the potential to reduce experienced overpressure on breachers, makes tamping a desirable tool not only from an efficacy standpoint for breachers but also from a safety standpoint for operational personnel. The long-term consequences of blast exposure are an open question and may be associated with temporary performance deficits and negative health symptomatology. PURPOSE: This work evaluates breaches of varying charge weight, material breached, and tamping device used to determine the value of tamping during various scenarios by measuring actual breaches conducted during military and law enforcement training for efficacy and blast overpressure on Operators. METHODS: Three data collections across 18 charges of various construction were evaluated with blast overpressure sensors at various distances and locations where breachers would be located, to assess explosive forces on human personnel engaged in breaching activities. RESULTS AND CONCLUSIONS: Findings indicate that water tamping in general is a benefit on moderate and heavy charges but offers less benefit at a low charge with regard to mitigating blast overpressure on breachers. Reduced overpressure allows Operators to stage closer to explosives and lowers the potential for compromised reaction time. It also reduces the likelihood of negative consequences that can result from excessive overpressure exposure and allow Operators to "do more with less" in complex environments, where resource access may be limited by logistic or other limitations. However, tamping in all instances improved blast efficacy in creating successful breaches. Future studies are planned to investigate tamping mediums beyond water and environment changes, whether tamping can be used to mitigate acoustic insult, and other explosive types.

Neurocognitive Performance Deficits Related to Immediate and Acute Blast Overpressure Exposure.

Addressing the concerns surrounding blast injury for the military community is a pressing matter. Specifically, sub-concussive blast effects, or those blast effects which do not yield a medical diagnosis but can result in symptom reporting and negative self-reported outcomes, are becoming increasingly important. This work evaluates explosive blast overpressure and impulse effects at the sub-concussive level on neurocognitive performance assessed with the Defense Automated Neurobehavioral Assessment (DANA) across seven breacher training courses conducted by the US Military. The results reported here come from 202 healthy, male military volunteer participants. Findings indicate that the neurocognitive task appearing most sensitive to identifying performance change is the DANA Procedural Reaction Time (PRT) subtask which may involve a sufficient level of challenge to reliably detect a small, transient cognitive impairment among a healthy undiagnosed population. The blast characteristic that was consistently associated with performance change was peak overpressure. Overall, this study provides evidence that increasing blast overpressure, defined as peak overpressure experienced in a training day, can lead to transient degradations in neurocognitive performance as seen on the DANA PRT subtask, which may generalize to other capabilities.

The Role of Very Low Level Blast Overpressure in Symptomatology.

Blast overpressure exposure has been linked to transient, but measurably deteriorated performance and symptomatologies in law enforcement and military personnel. Overlapping sub-concussive symptomatology associated with the very low level blast overpressures (vLLB) but high sound pressure (<3 psi) associated with these exposures has largely been ignored. Notably, the current vLLB or acoustic literature has focused exclusively on auditory defects, and has not addressed the broader concerns of Soldier health and readiness. This work was prompted by reports of symptomatology such as headache, nausea, slowed reaction time, and balance/hearing complications among personnel undergoing frequent exposures to low overpressure accompanied by high acoustic pressures. To more fully address the consequences associated with low overpressure exposures (<3 psi), a pilot proof-of-concept study was implemented, and data was acquired at two sites on the Fort Benning grenade course range. Findings indicated overpressures ranged from 0.14 to 0.42 psi (0.97-2.89 kPa) at range 1 and 0.22-0.30 psi (1.52-2.07 kPa) on range 2 of the grenade course. Corresponding sound-meter data varied from 153.72 to 163.22 dBP. Headache and long think were the most frequently reported symptoms (3/6 instructors), with lightheadedness, ringing of the ears, restlessness, frustration, and irritability also increasing in 2/6 of the instructors post exposure. Long think (prolonged thinking), ringing of the ears, restlessness, and irritability were the most severe symptoms, with the highest reported post exposure value rating a 3 on the 0-4-point scale. We demonstrate that low-level repeated overpressure exposure can result in transient symptomatology that overlaps with sub-concussive like effects.