THE INNERMOST SECRETS OF HELMET SAFETY

August 10, 2012
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There is one question that never gets answered. Oh, people try to put a good spin on it, but deep inside the recesses of their minds, they have doubts. That question is, “Will my helmet actually protect me in a crash?”

The most obvious answer is, “Yes, of course your helmet will protect you in a crash.” Its woven fiberglass, Kevlar-reinforced, expanded-polystyrene construction is designed to keep your fragile skull (and its contents) from being splattered all over the ground. Helmets do work, and there are thousands of people who have crashed who will testify to this fact. In no way are we decrying the benefits of wearing a helmet. But, when talking about how well your helmet will protect you in a crash, you have to narrow your focus to one part of the human anatomy: the brain. In much the same way that a hulking lineman’s number one job is to protect the quarterback, a helmet’s main purpose is to protect the brain.

The human brain is fragile. It isn’t layered like muscle, sinewy like gristle or dense like bone. The human brain is a gelatinous mass that floats in a pool of cervical spinal fluid. Thanks to its container-like dura and the thickness of the skull, the human brain is protected from the normal wear and tear of daily life. You can cut your scalp, get a bump on your forehead and abuse your hair with Rogaine without causing any damage to the brain. The human skeleton and its internal parts are structurally designed to withstand activities that are human-powered, but not speeds or impacts that are mechanically enhanced, such as with motorcycles. Perhaps the limits of the integrity of the skull end when a collision occurs at a maximum running speed (about 25 miles per hour).

THE ANATOMY OF A HELMET

When man exceeds his physical limits, he needs to increase his level of protection?thus motocross racers wear helmets. A motorcycle helmet is a two-part design that works to enhance the natural protection of the skull and dura. The two parts of a helmet are the outer shell and the inner liner.

The outer shell. Outer shells are molded from either fiberglass, resin, carbon fiber or Kevlar. They can also be made from ABS or polycarbonate thermoplastic. In layman’s terms, the shell acts as an artificial skull. It deflects sharp objects, offers the skull an abrasion-resistant skid pad and is the equivalent of an automobile’s crumpling fenders as it cracks, delaminates and crushes on impact.

The inner liner. A helmet’s inner liner is made of expanded polystyrene (EPS). An EPS liner is essentially a beer cooler that surrounds the skull. Think of the inner liner as an airbag for your brain. When your helmet hits the ground, the fiberglass outer shell takes the brunt of the initial impact. As the fiberglass is pushed inward by the force of the blow, the softer EPS liner, between the outer shell and your brain, begins to crush. If all is right with the world, the EPS liner absorbs the energy of the impact at a rate that does not allow the spike of energy to reach the skull with significant force, or to rebound back like a basketball. The inner liner’s job is to absorb the energy and bring your head to a gentle stop (simultaneously crushing from the outside the impact with the ground and crushing from the inside as the weight of the human head continues forward).

If your helmet has the proper structural rigidity and crushability in the outer shell to disperse the impact of the ground, and its inner liner has enough EPS foam (of the proper density) to absorb both the impact of the ground and the forward momentum of the skull, you will get up and walk away.

But, and this is a big but, the guy who designed your helmet had to make an educated guess about how hard you were going to crash. From this guess, he selected the number of layers of fiberglass cloth, the amount of resin required and the overlay pattern of the cloth strips that would absorb this projected energy spike. From a wide range of EPS densities, he selected the inner liner that would best absorb the force of the prototypical crash. He also determined how thick the foam liner would be and whether to run different densities in different parts of the foam inner liner’s skull cap. If he guessed right and you crash exactly as he predicted, then your chosen helmet will protect your lovely brain.

But, he doesn’t know you. He has never seen you ride. And even if he guesses right, you still face another danger, one that is best described by the word “sloshing.”

WHAT IS SLOSHING?

What is sloshing? When your motorcycle is doing 35 mph, your helmet is also doing 35 mph, and thus your brain is doing 35 mph. When you crash, however, your motorcycle goes from 35 mph to zero in a split second. When your helmet hits the ground, it goes from 35 mph to zero as well.

But, your brain does not stop. It keeps right on going at 35 mph until it sloshes into the front half of the skull. Now, instead of coming to a stop at zero mph, the human brain sloshes back in the opposite direction of travel. This scenario creates incredible injuries, including bleeding in the brain, shearing of the brain tissue and swelling?none of which is good.

Want some good news? It is possible to design and build a helmet that would protect the human brain from damage in a motorcycle crash. There are designs that would absorb all the energy and bring your delicate brain to a gentle stop. The only problem? You wouldn’t want to wear that helmet.

As the emeritus professor of the University of Southern California’s head protection research laboratory, Harry Hurt told the MXA wrecking crew many times, “Tell me what kind of crash you are going to have and I will build you a helmet that will protect your brain.” Then he laughed and said, “But you wouldn’t be able to move your head.” Helmets with 6 inches of foam that look like they would fit the Jack-in-the-Box spokesman don’t appeal to most racers.

WHAT CAN YOU DO TO PROTECT YOURSELF?


There are four major helmet-testing certification programs: DOT (Department of Transportation), ECE (the Euro standard that is accepted in over 50 countries), BSI (the British standard) and Snell (a private-testing standard used in the USA). No helmets are tested on human subjects (at least not in the lab), so to come up with comparable test standards, they rely on an accelerometer to precisely record the G-forces a weighted head form generates when stopping (and the amount of time it takes). Most insiders believe that the DOT standards are the least intense and thus reward the softest EPS foam, while the Snell standards are the toughest and thus demand stiffer foam. This generalization is true, but as helmet technology has improved, the ECE and Snell standards have grown closer together?although they are still not identical.

Helmet testing is the subject of controversy. Which certification is best? Do the helmets on the shelf actually meet the standards that the sticker would lead one to believe? Is ECE better than DOT? Is Snell better than all the others?

One thing is sure, helmet testing is based on an assumption that the scientists can determine a threshold of injury. That threshold used to be 400 Gs, then it was 300 Gs. And, if 300 Gs is good, then wouldn’t 200 Gs be better?Will a G-force load of 200 Gs over 2 milliseconds kill you? Not you, but maybe somebody. Like who? Somebody who has suffered a severe head injury before, or somebody who is older?say, over the age of 50.

STICKER SHOCK AND STICKER CONFUSION

When it comes time to buy a new helmet at your friendly local dealer, you will find helmets with stickers from DOT, Snell or ECE (you are unlikely to find a BSI sticker, unless you are in England or it is piggybacked with another certification sticker). Which one is the best? We wish we knew, and we wish that the scientists who devised these test knew?but they don’t.

Is a DOT-certified helmet less safe than a Snell-certified helmet? Yes and no. It depends. Even the AMA has hedged its bets over the years, pulling away from requiring Snell certification to the less rigorous DOT standard (all helmets sold in the USA must meet the DOT standard). The AMA did this because they did not want to be subject to a lawsuit from a trial lawyer ready to prove that some other certification, above or below the federally mandated standard, was the cause of his client’s death.

When most people purchase a helmet, the decision-making process is typically driven by the helmet’s shape, graphics, comfort and status more than the safety sticker on the back. Since the consumer does not know the difference between one certification standard and the other, he isn’t equipped to make an educated decision.

WHICH HELMET SHOULD YOU BUY?

So which helmet should you buy? We are not going to say that it doesn’t matter, but when it comes to safety, you are dealing with forces beyond your control. The Department of Transportation didn’t know that you were going to miss a gear on the face of a 100-foot tabletop, and Snell didn’t know that you were going to fall over at “laugh-in” speed. Over a 100-foot tabletop, most people would agree that Snell’s tougher standards would deliver the most protection; however, in a low-speed tip-over DOT’s lower G standard might be better.

Your decision should be made based on the quality of the helmet and the features that are important to you. That might mean a DOT, ECE, BSI or Snell sticker, but it should also include the caliber of construction, engineering behind the design, added features and personal preference. Ultimately, helmet safety comes down to wearing the best helmet you can afford (and there are excellent helmets that don’t have big price tags), replacing your helmet after every head-banging crash (if the EPS foam is crushed in one spot, that spot is no longer safe), and riding within the limits of your health insurance and tolerance for pain.

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