A new generation of hard hats is promising better protection against on-the-job concussions, also known as mild traumatic brain injuries.

These hard hats incorporate technology that not only protects the head from a direct impact, but also from a glancing blow that causes the head to rotate suddenly – a major cause of concussions.

"The human brain is readily injured by a rotational force," says Michael Bottlang, director of the Legacy Biomechanics Lab in Portland, Ore. For example, he says, a boxer will "drop like a fly" from a punch to the chin that causes the head to turn rapidly.

So Bottlang and Dr. Steven Madey, an orthopedic surgeon in Portland, have developed a hard hat intended to absorb rotational force. It's made and sold by WaveCel, a company the two men founded to make safer bike helmets.

The WaveCel hard hat is just the latest effort to update the products, known as industrial safety helmets, which brain injury experts say are overdue for an upgrade.

"Unfortunately, today's most frequently used hard hats look identical to the ones from the '60s," Bottlang says.

MIPS, a Swedish company, offers a competing technology to protect a worker's brain from sudden rotation.

Upgraded helmets like these, "are keeping the brain more stationary, and that has a lot of potential benefit," says Dr. Brandon Lucke-Wold, a neurosurgeon at the University of Florida who has no ties to the helmet industry.

Understanding workplace concussions

About one-fourth of all concussions among adults occur on the job, especially at construction sites. Falls, which often cause the head to turn or tip suddenly, are the most frequent cause.

One reason workplace brain injuries are so common is that hard hats — unlike sports helmets — haven't changed much since their invention a century ago.

Lucke-Wold, who often treats patients with brain injuries, wears a state-of-the art bike helmet during his daily commute.

"But the construction workers I saw biking home today were wearing hard hats that are very similar to what I saw 10 to 15 years ago," he says.

A typical hard hat consists of a plastic outer shell with an inner suspension system made from webbing. Some models include foam padding on the sides and a chin strap.

This design is good at protecting the brain from direct hit, say a hammer dropped by a worker two stories up. But traditional hard hats aren't so good when the impact comes at an angle.

Studies show that's because an oblique impact can cause the helmet, and the head inside it, to turn suddenly and violently. And a growing body of research shows that the brain is highly vulnerable to this sort of rotational force.

The reason is that the brain is a bit like an egg yolk — a soft capsule surrounded by liquid, and contained inside a hard shell.

You can shake an egg forcefully without disrupting the contents. But experiments show that if you spin one hard enough, the yolk inside will rupture even though the shell remains intact.

Most hard hats act like an egg shell.

"They do a job at reducing force, so they serve a purpose," Madey says. "But if they're not optimized to decrease the spin, they're not optimized to prevent injury."

A helmet that works like sand

Madey and Bottlang initially founded WaveCel to make better sports helmets.

Their inspiration came from observing what happens to a ball when it strikes the ground at an angle, the way a biker's head often does in a crash.

The ball doesn't just bounce, Madey says. "It will hit the ground, it'll have friction and it'll create spin."

Unless the ground is made of sand.

"If you throw a ball into a sandpit, the sand gives underneath, it doesn't impart spin to the ball," Madey says. And the ball doesn't bounce.

So Madey and Bottlang developed a helmet liner made from a special plastic honeycomb designed to act like sand.

"The honeycomb structure is a very light, breathable material that is not only good at absorbing linear force, but also breaks that spin the way sand would," Madey says.

The WaveCel liner can be found in several big-brand sports helmets.

An independent study found that bike helmets with either WaveCel or MIPS technology were better than conventional helmets at reducing rotational force. A study led by Bottlang and Madey found that WaveCel outperformed MIPS for the type of head impacts caused by falls.

One potential barrier to widespread acceptance of the new helmets is price.

WaveCel hard hats cost $169 to $189, which is several times the amount for a standard hard hat and more than many premium models, including some with MIPS technology.

"If I have one goal in the next few years, it's to bring the price down," Bottlang says.