A helmet wouldn’t really protect your brain if you stand less than a foot away from 3 grams of TNT when it explodes, but a simple face shield attachment would help defray the blast energy from your brain.
A new study from the Institute for Soldier Nanotechnologies used computer simulations to show that traumatic brain injuries (TBI) could be reduced with a redesigned helmet. The study appeared in Proceedings of the National Academy of Sciences on Monday.
While civilians usually suffer these types of injuries from falls, car crashes, and sports collisions, military personnel in war zones suffer TBI from explosive devices. These blasts cause 60% of all combat casualties. About 130,000 men and women deployed to Iraq and Afghanistan sustained these injuries – ranging from concussions and long-term brain damage to death.
The Advanced Combat Helmet – which provides ballistic and impact protection without degrading field of vision and hearing – has been Army-issued for at least six years. But a recent study from Lawrence Livermore National Laboratory scientists concluded that these helmets actually make brain injuries worse by focusing the blast energy.
To reexamine that claim, MIT aeronautic engineer Raul Radovitzky and his colleagues used detailed simulations to see how stress waves move through the face and skull into the brain after an explosion. To create the models, the team collaborated with a neuroscientist at the Defense and Veterans Brain Injury Center at Walter Reed Army Medical Center and used MRI to model features of the head.
Their 3-D computer model head even consisted of skin, fat, muscle, gray and white matter, eyes, and sinuses. And they simulated the blast conditions of a TNT explosion to the face of a 150-pound human standing about half a foot away – which is equivalent to compressing air to 10 times its normal pressure.
They ran three scenarios, blasting energy at a head wearing no helmet, a helmet, and a helmet with a face shield.
The combat helmet, the team discovered, doesn't help a lot for blast protection, but it doesn't make it worse.
Compared with the unhelmetted, unprotected face, the combat helmet delayed the shock wave’s arrival into the brain, but it reduced the stress only slightly. It “does not worsen the negative effects of a blast wave – does not enhance the energy of the blast – as has been previously suggested," Radovitzky says. "But we also find that it doesn't really help much; it doesn't mitigate the blast wave significantly."
They found that the soft tissues of the face were the main pathways for the pressure waves from the blast to enter the brain tissue.
"There's a passageway through those soft tissues directly into the brain tissue, without having to go through bone or anything hard," says Radovitzky.
But, as the director of neurotrauma research for the US Army's Medical Research and Materiel Command points out: "Models are only as precise as the data available to drive them."
Radovitzky admits that there are many other aspects of a face shield add-on that need to be considered, “like how you would affect the situational awareness of the soldier, how they can operate without being hindered by the device." Just what form or shape the face shield should take remains open for discussion, but the MIT researchers have talked with an Army laboratory that develops equipment for soldiers.
Top image: Advanced combat helmet / US Army
Middle image: Anatomical features of the brain analyzed using models that simulate explosive blasts / Michelle Nyein
Bottom image: Head model with helmet and conceptual face shield / PNAS Nyein et al.