Helmet design and safety are topics where there doesn’t seem to be a clear answer. Instead, helmet safety qualities fall into the category of unanswerable questions like “Which engine oil is the best?”

Lately, there has been a lot of discussion about whether helmets should be softer or harder.  Even the standards for helmet testing have come under fire.  Now there are at least three governmental testing standards that measure a helmet’s safety differently.

New technologies

Some helmet manufacturers are incorporating new technologies into their helmets.  These technologies supposedly offer greater safety. For example, some helmets now offer a Multi-directional Impact Protection System (MIPS) system.  Another manufacturer’s helmet design incorporates an hourglass-looking shock absorber.   But even with all these helmet technologies, the question of what makes the safest helmet goes unanswered.

glancing off

Japanese “premium” helmet manufacturer Arai thinks that one safety parameter often goes unnoticed but is extremely important for helmet safety.  Arai calls that parameter “glancing off.”  According to Arai:

“It is the helmet’s ability to slide past or “glance off” objects that can reduce the amount of energy sent directly into the helmet – instead, dispersing as much of it as possible without stopping.

Glancing off – protecting against more than direct impacts

In other words, Arai thinks there is more to helmet safety than just impact.  In a crash, energy is created.  And the role of the helmet is to “appropriately manage the impact energy directed to the rider’s head.

Energy management may be achieved by “absorption” of the impact energy around a rider’s head.  In an impact, the outer shell deforms, and the cells of the inner EPS liner crush.  These two traits manage impact energy by converting it into work.  But according to Arai, managing impact energy isn’t just absorbing it and requires more.  They believe a vital attribute of a helmet’s energy management is its ability to “glance off” obstacles.

Limited capability

Arai claims that when any helmet manufacturer talks about “impact absorption ability”, there is a limit to how much energy a helmet can handle regardless of the manufacturing technique employed.  That’s because there is a limit to the space between the helmet’s shell and the rider’s head. Therefore, if the impact energy exceeds the capabilities of the impact-absorbing material, the remaining energy can be transmitted to the rider’s head.

glancing off

The amount of energy any helmet can absorb is limited.

So given that any helmet’s impact-absorbing capability is limited, Arai says that a helmet must be able to “glance off” instead of just trying to mitigate impact absorption.  And they point to today’s testing standards as failing to recognize what they see as an essential helmet characteristic.

Glancing off

Most current helmet testing standards concentrate on impact absorption but don’t test a helmet for its ability to “glance off.”  There are test procedures that test impact energy and a helmet’s ability to resist penetration.  However, there is no test procedure to test a helmet’s ability to “glance off” an obstacle, thereby reducing the energy subjected to the head.

That’s because it’s challenging to put numbers to the helmet’s shell form and determine its ability to glance off.  And although all helmets have some ability to glance off, there’s still no definition as to what constitutes a failure or pass in “glancing off.”  Unfortunately, today’s safety standards don’t consider a helmet’s ability to glance off obstacles.

Test procedures

You may be thinking, “So what?”  The current tests are good enough for me.  Frankly, I’d not considered a helmet’s glancing off capability until I found out about some of today’s testing parameters.

Take, for example, the helmet drop test from the strictest helmet standard testing in the world.  During the test, a helmet drops from a height onto a metal anvil below.  If you convert the force from this test into impact speeds, the most demanding standard in the world only tests the helmet’s capability to manage a maximum speed of roughly 17 mph (28 kph).  In a world where vehicle speeds are generally over 30 MPH, the test procedures suddenly don’t feel real-world oriented.

Another test procedure checks the helmet’s ability to resists penetration.  It uses a 3 kg (6.6 pounds) striker.  Releasing the striker from a height of 3 meters (9 feet 10 inches), the pointed striker drops onto the helmet.  Penetration beyond a certain limit will cause the helmet to fail the test.  As you can see, each of these test procedures only tests helmets for their ability to mitigate direct impacts.

glancing off

Untested parameters

But no test procedures check the helmet’s ability to reduce impact force to the rider’s head by glancing off obstacles.  And that seems like a serious omission.  While direct impacts certainly are very important, a helmet’s ability to reduce the energy transmitted to a rider’s head before having to be absorbed seems to be an essential consideration.

This is not to say that the current helmet safety standards are wrong. It just says that there is at least one other important consideration in testing for a helmet’s ability to protect a rider.  That parameter is a helmet’s ability to glance off objects.  And presently, no helmet testing standard tests for this ability.   Hopefully, this will change in the future.

But until then, if you’d like to learn more about glancing off and the test procedures used to test helmets, Arai has an excellent downloadable brochure about the importance of “glancing off.”

 

 

All image credit: Arai

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