As discussed in the email to Congress and the Military below, the rigid skull AND the kevlar helmet shell actually flex under the impact of the supersonic blast wave from an IED. Such flexure causes significant brain injury with resulting disability or death. Rigid helmet pads pass through the kevlar shell flexure to the skull, adding to brain injury.
Lawrence Livermore National Research Laboratory study of brain injury from blast wavecan be reviewed here. (click on the blue stuff).
“Skull Flexure from Blast Waves: A New Mechanism for Brain Injury with Implications for Helmet Design”
“Traumatic brain injury [TBI] has become the signature injury of current military conflicts. The debilitating effects of TBI on society are long-lasting and costly. Although the mechanisms by which impacts cause TBI have been well researched, the mechanisms by which blasts cause TBI are not understood. Various mechanisms, including impacts caused by the blast, have been investigated, but blast-induced deformation of the skull has been neglected. Through the use of hydrodynamical numerical simulations, we have discovered that non-lethal blasts can induce sufficient flexure of the skull to generate potentially damaging loads in the brain, even if no impact occurs. This mechanism has implications for the diagnosis of TBI in soldiers and the design of protective equipment such as helmets. “
“…For ACH-style foam-padded helmets, underwash (blast wave ‘washing’ under the helmet, causing skull flexion) is mostly prevented but the helmet is more strongly coupled to the head, so helmet motions (bulk acceleration) and helmet bending deformations are transferred directly to the skull. The specific response is sensitive to the rate-dependent mechanical stiffness of the foam, which is not a well-measured quantity. Consequently, we compared simulations using a foam stiffness measured at low-rates with those using a foam three orders of magnitude stiffer. Stiffer foams transferred greater loads from the helmet to the skull, reducing the helmet effectiveness against overpressure.”
“An effective mitigation strategy against the deleterious effects of skull flexure would be to deny the blast wave access to the airspace under the helmet, and then either incorporate rigidity into the helmet itself, or design the helmet suspension system so that the flexure of the helmet is not transferred to the skull” (via too-firm pads…emphasis and explanation in italics are mine).
Their summary notes the solution to kevlar/skull-joined flexing that causes brain injury to be either amore rigid helmet or a less rigid pad system. One has to do a lot of inferences in all computational modeling, but this one seems very sound in saying that too firm pads make the skull flexion problem worse. Softer pads decrease under-helmet skull flexure.
In the meantime, the military is ignoring research data showing the current GI pads to be ineffective in protecting our warriors from TBI (Traumatic Brain Injury) due to the blast wave itself, separate from impact. Here’s my most recent email to the Senate and House Armed Services Committees. to: ‘Lomonaco, Jeff (Franken)’; ‘Sutey, Bill (Armed Services-Senate)’, Tolleson, Jesse (House).
13 Feb, 2010: Gentlemen: The news keeps coming out about the lack of TBI protection from the current military helmet/pad combination. It reiterates the findings of studies at Rochester (Blackman) and Livermore (Moss/King/Blackman) showing :
- ACH/MICH (and LWH by extension) helmets now have pads that transfer blast-wave induced flexure of the Kevlar shell to the brain via pads that are too firm. This worsens the skull flexure that occurs from underwash around the pads. Although the skull flexure may only be measured in microns, the brain damage is immense due to the rapid onset. (http://arxiv.org/ftp/arxiv/papers/0809/0809.3468.pdf)
Here are the current reviews: http://www.pppl.gov/colloquia_pres/WC25MAR09_EBlackman.pdf is an excellent Power Point/PDF presentation by Blackman that stresses the current pad/helmet system does NOT protect from TBI due to the ‘rigid’ connection between the helmet and skull (Slide 58). Ignored, of course, by military.
http://www.sciencecodex.com/llnl_research_reveals_how_blast_waves_may_cause_human_brain_injury_even_without_direct_head_impactsis another summary of known data, reflecting the pads in use do NOT protect from blast-wave induced skull ‘ripple’ due to their rigidity.
The authors also posit that the blast wave itself causes an additional rigidity to the foam structure of current pads, adding to the brain injury due to the supersonic blast wave. I find no research on the Web showing a comparison of the various pads available as to which might be less affected from that.
How long does it take for the military to actually utilize the fruits of national research institutions backed by ‘the word’ from combat troops and give our warriors the protection and wearability they demand in their head armor?
We get emails by the hundreds/thousands from warriors complaining of the rigidity of their helmet pads and asking for our help in obtaining the same helmet pads (Oregon Aero) that Natick approved for the first 500,000+ ACH; that were in use prior to the military changing to Team Wendy and MSA pads as a cost-saving venture. TBI is costing the US taxpayer approximately 1.5 billion bucks a year and costs the warrior and his family for the rest of his/her life. This rigid stance (as well as helmet pads) by the military makes no sense. ..