Head Blast Protection

One of the more poignant talesout of the Second World War reports on a bitter cold winter’s night in which a Finnishunit was bracing for a heavy soviet assault coming from over a rise to thefront.  Their artillery sent over a barrageof high explosive that exploded in the air into the face of the Soviets.  After which nothing happened.

After some time, patrols weresent out to see what was happening.  Anentire Soviet regiment was laid out in position to jump off out in theopen.  They had all been killed formshock wave proximity.  In this case if mymemory serves me we are talking several thousand in place for a mass assault.

Obviously a visor is needed to ablatethe shock, but it also needs to be out of the way a lot of the time or soldierswill soon toss them.  This will be adifficult design problem. A god plan may be to design the function into the gasmasks.    The periods of vulnerability and need tend tooverlap and soldiers will put more value on the mask as shock protection in theface of incoming artillery and unlikely gas.

Helmet Visor Could Protect Troops From Shock Waves

November 22, 2010  |  

Adding a face shield to the standard-issue helmet worn by U.S. troops could help protect soldiers fromtraumatic brain injury, the signature wound of the recent wars in Iraq and Afghanistan. A new study thatmodels how shock waves pass through the head finds that adding a face guarddeflects a substantial portion of the blast that otherwise would steamroll itsway through the brain.

The study, to appear in the Proceedings of the National Academyof Sciences, is part of a spate of new work tackling traumatic brain injury. Anestimated 1.5 million Americans sustain mild traumatic brain injury each year,and nearly 200,000 service members have been diagnosed with it since 2000,according to the Armed Forces HealthSurveillance Centerin Silver Spring, Maryland.

While direct impact, such as banging the head, clearly can injure thebrain, the forces endured when explosives send shock waves crashing through thehead are much more difficult to characterize.

In the new study, researchers led by Raúl Radovitzky of MIT’s Institutefor Soldier Nanotechnologies created an elaborate computer model of a humanhead that included layers of fat and skin, the skull, and different kinds ofbrain tissue. The team modeled the shock wave from an explosion detonated rightin front of the face under three conditions: with the head bare, protected bythe currently used combat helmet and covered with the helmet plus apolycarbonate face shield.

The results showed that today’s helmet doesn’t exacerbate the damage,as some previous research had suggested. But at least in terms of blastprotection, the current helmet doesn’t help much either. Addition of a faceshield would improve matters, the team reports.

“The face shield contributes a lot to deflecting energy from the blastwave and not letting it directly touch the soft tissue,” says Radovitzky.“We’re not saying this is the best design for a face shield, but we’re sayingwe need to cover the face.”

To validate the model, researchers at MIT and elsewhere will have to conductexperiments in the real world. But the work points to an intrinsic flaw in thecurrent helmets.

“These helmets weren’t designed to stop a pressure wave; they weredesigned to stop bullets,” says Albert King, director of the Bioengineering Centerat Wayne StateUniversity in Detroit. “Just like a football helmet wasn’tdesigned to stop a concussion, but to stop skull fracture.”

Designing a blast-resistant helmet requires a better knowledge of whathappens in the brain when an explosion washes over it. Soldiers experiencingexplosions often describe a wind or wave that makes them see stars. “I reallygot my bell rung,” is a common report.

The resulting “mild” traumatic brain injury doesn’t lead to long-termloss of consciousness, and brain scans yield normal results. But labeling theseinjuries as mild is a misnomer, says Douglas Smith, director of the Center forBrain Injury and Repair at the University of Pennsylvania in Philadelphia.

“It is not mild; that term has led people astray,” says Smith. “It issomething very serious that can lead to severe dysfunction.”

Smith and his colleagues have been working on a sensor that could beplaced in a helmet or vehicle and that, like the radiation badges worn bynuclear-plant workers, would indicate exposure to blast forces likely to causebrain injury. The sensor is described in a paper to be published in NeuroImage.

While a sensor would indicate exposure to blast forces, it still isn’tclear exactly how that energy translates into brain trauma. Under everyday conditions,the brain can easily withstand a little jostling. “Plop down in your chair andyour brain blobs around like Jell-O,” Smith says. But at tremendously highspeeds, instead of gently stretching, brain cells can snap and break (SN: 3/13/10, p. 11)like glass.

The long-term effects of these busted brain cells are largely unknown.In addition to chronic headaches, vertigo and difficulty remembering words,research suggests that when the brain shuts down for even a few minutes,depression is more likely down the road.

Scott Matthews, a psychiatrist at the University of California, SanDiego, who studies mild traumatic brain injury in returning veterans, notesthat causality can’t be established. But among soldiers who were exposed tocombat, he sees depression twice as often in people with traumatic braininjury.

“There’s more and more evidence that loss of consciousness changes thebrain,” Matthews says.

Unraveling cause and effect and designing useful experiments toilluminate traumatic brain injury and its aftermath remains extremelychallenging. And translating those scientific findings into meaningful policycan be just as difficult. Even implementing something as simple as a helmetwith a face shield poses problems, says Smith.

“How do you deploy something like that?” he asks. “There are practicalthings like temperature issues. And then there’s wanting soldiers to be able tomeet and greet in villages without looking like spacemen.”

Image: Computer model of the head./Michelle Nyein.

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