Combat helmet should cover face: current model lets blast forces into brain, simulations show.

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

Nearly 200,000 service members have been diagnosed with mild traumatic brain injury since 2000, according to the Armed Forces Health Surveillance Center in Silver Spring, Md. While blunt impact clearly can injure the brain, the forces that are endured when explosives send shock waves crashing through the head are much more difficult to characterize.

Researchers led by Raul Radovitzky of MIT's Institute for Soldier Nanotechnologies created a computer model of a human head that included layers of fat and skin, the skull, and different kinds of brain tissue. The team modeled the shock wave from an explosion detonated right in front of the face under three conditions: with the head bare, protected by the current combat helmet and covered with the helmet plus a polycarbonate face shield.

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The study, published online November 22 in the Proceedings of the National Academy of Sciences, showed that today's helmet doesn't exacerbate the destructive force of an explosion, as some previous research suggested. But at least in terms of blast protection, the current helmet doesn't help much either. Adding a face shield would improve matters, the team reports.

"The face shield contributes a lot to deflecting energy from the blast wave 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 saying we need to cover the face."

To validate the model, researchers will have to conduct more experiments in the real world. But the work does point to an intrinsic flaw in the current helmets.

"These helmets weren't designed to stop a pressure wave; they were designed to stop bullets," says Albert King, head of the Bioengineering Center at Wayne State University in Detroit. "Just like a football helmet wasn't designed to stop a concussion, but to stop skull fracture."