Researchers Find a Flaw in Modern Military Helmets

Photo credit: Duke University
Photo credit: Duke University

From Popular Mechanics

  • Researchers subjected military helmets from World War I and today to primary blast testing.

  • Helmets for military use have focused on preventing artillery and striking injury, not primary blast.

  • The force wave generated by an explosion itself is the primary blast, where moving air strikes the body.

In a new paper, researchers compare 100-year-old military helmet technology to what soldiers use today, and the results may surprise you. These researchers wanted to study how helmets endure primary blast neurotrauma, which is a little-considered aspect to what helmets can do to protect soldiers.

The National Institutes of Health (NIH) hosts a 1986 paper that defines the levels of blast injury:

“Injury from explosion may be due to the direct cussive effect of the blast wave (primary), being struck by material propelled by the blast (secondary), to whole-body displacement and impact (tertiary), or to miscellaneous effects from burns, toxic acids, and so on. Severe primary blast injury is most likely to be seen in military operations but can occur in civilian industrial accidents or terrorist actions.”

Essentially, primary blast is the force of the explosion itself doing things like banging your brain against the sides of your skull. The Centers for Disease Control and Prevention (CDC) says primary blast force most directly affects a surprising kind of body structure: “Gas filled structures are most susceptible—lungs, GI tract, and middle ear.” A condition called blast lung is the most harmful primary blast injury, the CDC says, but concussive brain injury is still a big deal.

More importantly, military helmets haven’t been designed with this kind of injury in mind. That’s not anyone’s fault, but study of traumatic brain injury has accelerated in recent decades especially as more scientists study the lifelong effect on football players. We’re in a position now where careful design could help protect people working in extreme situations from primary blast injuries along with the other injuries that helmets already work well against.

To test how well existing military helmets protect against these injuries, scientists from Duke University’s Department of Biomedical Engineering positioned helmets on dummy heads fitted with sensors. Then they used a shock tube to hit the helmets with force mimicking the kinds of bomb and shell blasts soldiers really experienced both historically and now. They also blasted a dummy with no helmet.

Photo credit: Duke University
Photo credit: Duke University

“Blast exposure to the bare head was more severe than any helmeted test for every blast intensity and at every measurement location,” the researchers conclude. “The bare head experienced three to five times higher peak pressures, which corresponds to higher risk of meningeal bleeding and other potential brain injuries.”

This might sound obvious, but remember these injuries are “only” blast force, not shrapnel or an object striking the head. Showing that a bare head experiences much higher risk of even “just” primary blast injury can help make the case that everyone in a risky area should always be in a helmet.

Photo credit: Duke University
Photo credit: Duke University

“Helmets provided more shock wave attenuation at lower pressure levels than at higher pressure levels, suggesting that helmets might play an especially important role in protection against mild primary blast induced brain trauma,” the researchers write. “The effect of wearing a helmet, especially for short positive phase durations, is a significant reduction in risk of blast brain injury at the crown of the head for overhead blast scenarios.”

In other words, like wearing a helmet on a bike, the massive overall reduction of risk even in milder blasts makes a helmet worthwhile at any time of any amount of risk.

And age is nothing but a number when it comes to primary blast injury. The current U.S. Army helmet is the Advanced Combat Helmet, or ACH. “While ballistic protection provided by helmets has increased significantly since WWI and saved many lives, the results found here suggest that the ACH did not perform quantitatively or qualitatively better than the historical helmets, and performed worse than the Adrian helmet for overhead primary blast at the crown of the head,” the scientists say. (The Adrian helmet is the one used by France in World War I.)

A few small changes could improve outcomes for soldiers who experience primary blasts in the line of duty. “In the future, helmet protection against primary blast might be improved by material choice, multiple material layers with different acoustic impedance, or the geometry of the helmet,” the researchers write. Now that’s using your head.

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source: yahoo.com