New interest in old helmet design

The helmet may be old, but the vision you are looking at is relatively new.

Credit: Joost Op ‘t Eynde, Duke University

Researchers from Duke University in the US recently tested three helmets from World War I and one from the present day to assess their performance in protecting the brain from shock waves created by nearby blasts.

Somewhat surprisingly, the century-old French Adrian helmet (right) came up trumps when compared with the Brodie and the Stahlhelm, used by UK/US and German troops respectively, and a current US combat variant, the Advanced Combat Helmet.

The reason, the researchers suggest, is that the ridge down the centre of the Adrian, which was designed to deflect shrapnel, helped deflect shock waves.

And that information is of more than just historical interest.

Biomedical engineer Joost Op ‘t Eynde says understanding how shock waves damage the brain is important because of advances in other protective equipment.

Helmets originally were designed primarily to protect from penetrating objects such as bullets and shrapnel, because blast waves would kill through pulmonary trauma long before they caused even minor brain damage.

Modern body armour protects the lungs, however, so the incidence of pulmonary trauma following a blast has dropped far below that of brain or spine injuries in military conflicts.

Previous studies suggest modern helmets provide a degree of protection from shock waves, Op ‘t Eynde says, but no currently deployed helmet has been specifically designed for blast protection – so he and colleague Cameron Bass decided to make a start.

They put each of the five helmets on a dummy’s head outfitted with pressure sensors at various locations, then placed the head directly underneath a shock tube, which was pressurised with helium until a membrane wall burst, releasing the gas in a shock wave. 

The helmets were tested with shock waves of varying strength, each corresponding to a different type of German artillery shell exploding from a distance of one to five metres.

The amount of pressure experienced at the crown of the head was then compared to brain injury risk charts created in previous studies. 

While all helmets provided a five-to-tenfold reduction in risk for moderate brain bleeding, the risk for someone wearing the old Adrian was less than for any of the other helmets tested.

That means that, despite significant advancements in protection from ballistics and blunt impacts, modern helmets may be no better at protecting the brain from shock waves created by nearby blasts than their World War I counterparts.

In the Adrian, the crest provided advantages not seen elsewhere, but there were other differences as well. For locations such as the ears, for example, performance appeared to be dictated by the width of the helmet’s brim and just how much of the head it covered.

And that’s exactly what the researchers wanted to know.

“The difference a simple crest or a wider brim can make in blast protection shows just how important this line of research could be,” Op ‘t Eynde says.

The results are reported in the journal PLOS ONE.