Non-lethal blast waves can cause human brain injury even without direct head impacts, which could lead to an enhanced understanding of head injuries and improved military helmet design, new research has suggested.
Using numerical hydrodynamic computer simulations, Lawrence Livermore scientists Willy Moss and Michael King, along with University of Rochester colleague Eric Blackman, have discovered that non-lethal blasts can induce enough skull flexure to generate potentially damaging loads in the brain, even without direct head impact.
Traumatic brain injury (TBI) results from mechanical loads in the brain, often without skull fracture, and causes complex, long-lasting symptoms.
TBI in civilians is usually caused by direct head impacts resulting from motor vehicle and sports accidents. TBI also has emerged among military combat personnel exposed to blast waves.
As modern body armor has substantially reduced soldier fatalities from explosive attacks, the lower mortality rates have revealed the high prevalence of TBI.
But, TBIs resulting from blast waves without head impacts have not been well understood.
To tackle this puzzle, the research team used three-dimensional hydrodynamic simulations to prove that direct action of the blast wave on the head causes skull flexure, producing mechanical loads in brain tissue comparable to those in an injury-inducing impact, even at non-lethal blast pressures as low as 1 bar above atmospheric pressure.
The Army's Advanced Combat Helmet replaced the older Personal Armor System for Ground Troops helmet.
Its Kevlar shell provides ballistic and impact protection, and its reduced edge cut, although reducing area of coverage, improves soldiers' field of vision and hearing.
In particular, the team showed that blast waves affect the brain very differently from direct impacts.
The primary source of injury from direct impacts is the force resulting from the bulk acceleration of the head.
In contrast, a blast wave squeezes the skull, creating pressures as large as an injury-inducing impact and pressure gradients in the brain that are much larger.
This occurs even when the bulk head accelerations induced by a blast wave are much smaller than from a direct impact.
"The blast wave sweeps over the skull like a rolling pin going over dough," said King, LLNL co-principal investigator.
Although the simulations show that the skull is deformed only about 50 microns, "this is large enough to generate potentially damaging loads in the brain," according to Moss.
"The possibility that blasts may contribute to traumatic brain injury has implications for injury diagnosis and improved armor design," he added.