A new study has recommended fitting face shields to combat helmets to better protect troops on the battlefield.
Greater use of body armour, called PPE or personal protective equipment, has allowed soldiers to survive violent explosions. But this has meant blast-induced traumatic brain injury has become the most prevalent military injury faced by soldiers in Iraq and Afghanistan.
A study by the United States military in 2009 found approximately 60% of combat casualties were the result of explosive blasts, resulting in some form of blast-induced traumatic brain injury.
Up to now, little has been known about the mechanical effects of blasts on the human head. Even less is known about how personal protective equipment, such as helmets, affect the brain's response to such blasts.
To get some answers, a team of researchers led by Raul Radovitzky from the Massachusetts Institute of Technology, tested the United States military's standard issue Advanced Combat Helmet (ACH).
Their report, which appears this week in the Proceedings of the National Academy of Sciences, examined the type of damage caused by the blast shock from a typical mortar attack or improvised explosive device (IED) - the most likely source for an explosive shock wave faced by troops in Iraq and Afghanistan.
Radovitzky's team used sophisticated three-dimensional computer models to investigate how explosive shock waves move through the cranium, cranial fluids and soft brain tissues of the human head.
They examined the impact of a blast wave against an unprotected head, head wearing a helmet, and a helmeted head fitted with a face shield.
Their simulations showed a typical frontal explosion compressed the air up to 10 times normal pressure. This energy was transmitted through the face into the skull and soft tissues.
Their results showed the ACH does little to protect soldiers from blast-induced brain injury, being only marginally better than no helmet at all in terms of mitigating blast shock.
The researchers found this was because the helmet didn't impede direct transmission of stress waves into the intracranial cavity. They also found slightly higher pressures where helmet padding touches the head.
But the simulations didn't support earlier claims that the helmets could actually increase brain injury by focusing blast energy.
Radovitzky's team found the best results were obtained by wearing a helmet fitted with a face shield. This reduced intracranial stresses to one-tenth of the pressure imposed on an unprotected head.
Professor Robert Vink, a neurologist at the University of Adelaide, says the study supports earlier animal tests, which reached the same conclusions.
He says the face shield makes a huge difference.
"It acts like a pressure deflector, you have this wave of pressure and the visor is like an aerodynamic device that makes the pressure go around the head."
Vink says the recent conflicts in Afghanistan and Iraq have shown a change in the type of threat soldiers face.
"Before, we focused on gun shot, but that's not the biggest issue now, it's blast," he says.
According to a Defence Force spokesperson, Australian troops are equipped with the Enhanced Combat Helmet (ECH), which is different to the ACH, but both are based on the Personal Armour System for Ground Troops (PASGT) helmet.