FORT DETRICK, Md. – An innovative study being undertaken by researchers at the U.S. Army Aeromedical Research Laboratory will provide vital data on the noise levels of small-arms fire, enabling the DOD to choose the best standard for protecting Warfighters from permanent hearing loss – an important contribution to preserving their physical and cognitive health and ensuring they are resilient and ready for the fight.
The Small Arms Noise Dose Escalation Research Project, or SANDER for short, is designed to provide DOD health experts with data that fills a crucial gap in available information about the damage to the human ear from repeated exposure to the concussive blasts of a discharging weapon. Dr. Heath Jones, lead USAARL researcher on the SANDER Project, says the study is intended to complement data obtained by previous studies conducted in the field.
“The field work can get us part of the way there, but a full understanding is going to require a tightly controlled experimental approach that meets the field studies halfway,” says Jones.
Hearing loss and tinnitus are the most prevalent service-related disabilities for U.S. veterans, according to the Department of Veterans Affairs. It is estimated that over half of combat veterans have moderately severe to severe hearing loss, and are 63% more likely to experience hearing loss as a result of military service than non-combat personnel. While research has demonstrated that repetitive exposure to the concussive blasts of small-arms fire increases the risk of hearing loss, researchers have not yet been able to quantify that risk in ways that allow for effective preventive measures.
That’s because it is more difficult to determine the damage to the cochlea – the hollow chamber in the inner ear that transmits sound vibrations to the auditory nerve – from exposure to short bursts of noise as opposed to damage from steady sound, which is better understood. Variations in intensity, duration, and level of exposure can cause different auditory injuries. In over 60 years of research, there is still no universal medical standard for assessing the risk of auditory injury from repeated exposure to blast and impulse noise.
“With properly fitted hearing protection and some consideration about the number of fired rounds a person is exposed to in a day, the risk of hearing loss is minimized, but it's very hard to assess the effects of hearing protection without a good sense of what damage the impulse does without that protection,” says Jones. “That’s one of the reasons we put together this study.”
With funding support from the Military Operational Medicine Research Program, Jones and the SANDER Project team designed a test apparatus consisting of standard shipping containers arranged in eight “arms” radiating from a center platform. On the center platform, Jones and his team will install a specially built device called a Blank Discharge Apparatus, or BDA. Designed and built with the assistance of the Oregon Ballistics Laboratories, an independent testing facility that specializes in ballistic and blast data collection, the computer-controlled BDA is capable of firing 72 blank rounds at intervals of anywhere from several seconds to a few hundred milliseconds. The BDA is designed to fire the blanks straight down, into ballistic rubber blocks placed on top of sand to prevent accidental injury.
In phase one of the experiment, subjects will first be tested to establish their individual hearing baselines, then fitted with pressure sensors and seated at the far end of each radiating arm. The subjects will be positioned both on top of the shipping containers and inside them, so that the researchers can assess the acoustic signatures of the noise impulses reaching them both in the open air and in the confined space of the shipping container. Jones and his team will then discharge the BDA once per day, gradually increasing the noise exposure each time, over a period of five days. Throughout the experiment, the subjects will be evaluated to determine the effects of the noise impulses on hearing and brain health from the repeated exposures.
Jones emphasizes that the study will not cause hearing loss in the subjects. The subjects will be exposed to noise until the researchers see a measurable shift in hearing thresholds, which will appear well before noise levels that would cause any risk of permanent hearing loss.
Following the completion of the experiment, Jones and his team will analyze the data they collected to establish the maximum tolerable noise impulse dose that Warfighters can safely be exposed to without experiencing a large, temporary change in their hearing threshold. The team will then analyze the empirical data to identify which of the currently available noise protection models comes closest to the maximum tolerable dose without exceeding it. Ultimately, the selected model will be recommended as the candidate for the DOD-wide noise protection standard for exposure to an allowable number of rounds of small-arms fire.
The SANDER Project, which officially kicked off in April, will be conducted over a five-year period. The first year will focus on acquiring and installing test equipment, refining the data collection and analysis process, and assembling and training the team. The second, third, and fourth years will involve running test subjects through the experiment and assessing the results. The final year will focus on analyzing the data collected and making a recommendation for the most appropriate damage risk criteria.
“With the SANDER Project, I think we're the closest we've ever been to addressing a problem that the military has been actively trying to solve since at least the mid-80s,” says Jones. “Hearing is extremely important, not just for operational reasons like being able to hear your teammates and identify threats on the battlefield, but also for Service Members’ quality of life.”
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