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September/October 2009

Helmets: Standards for Safety

F08 Subcommittee Specifies Protective Headgear

Today, more people than ever are playing a variety of sports and doing so longer into their lives. For many of these sports — football and pole vaulting, skating and cycling — there is a specially designed protective helmet.

When it comes to helmet design, consumers want safer, lighter, sleeker and possibly, cheaper. There are design and manufacturing considerations, and a marketplace loaded with helmet choices. Plus, members of Subcommittee F08.53 on Headgear and Helmets caution that we might not be able to have our entire wish list wrapped up in one helmet.

This is the backdrop against which F08.53, a part of ASTM Committee F08 on Sports Equipment and Facilities, has developed more than 20 helmet standards. The committee members listen to and address stakeholders’ requests; they analyze and collaborate. They use data from the volunteer efforts of committee members and their institutions or companies and, at times, from efforts funded by the National Institutes of Health.

Helmets and Energy Management

Helmet standards stand out in important ways because they specify or test headgear that protects the brain. And if there are impacts on the football or soccer field, for example, helmets need to cushion the blow.

Committee F08 members say it is all about energy management.

The ASTM helmet experts explain that a functioning helmet smoothes out energy spikes, called “g’s” for short. The g’s are the amount of gravity the earth exerts on you when you fall; a g is acceleration equal to the acceleration of gravity, approximately 32.2 feet per second for every second you are falling. If you hit your bare head on pavement the g reading spikes up straight. With a helmet, the g’s are managed and look more like a protecting bell curve, if you were able to see them on paper. That is how a helmet gives you the milliseconds needed to smooth out the spike and get those g’s under control. The helmet not only spreads out the impact duration, it is intended to reduce the magnitude of the linear acceleration of the head injury during an impact, according to Rick Greenwald, Ph.D., an F08.53 member, president of Simbex LLC in Lebanon, N.H., and an associate (adjunct) professor in the Thayer School of Engineering at Dartmouth College, Hanover, N.H.

The extent to which helmets are designed to prevent serious injury is well understood. “Helmets manage the risk of life-altering, catastrophic brain injury. In every study, helmets have proven to be 80 to 95 percent effective in preventing catastrophic brain injury,” says David Halstead, chair of Subcommittee F08.53, Committee F08 vice chair, technical director of the Southern Impact Research Center, Rockford, Tenn., where he oversees all technical aspects of testing, and director of the Sports Bio-Mechanics Lab and principal scientist at the Engineering Institute for Injury and Trauma Prevention, both at the University of Tennessee, Knoxville, Tenn.

A Specific Sport, A Specific Helmet

F08.53 helmet standards serve myriad active lifestyles through specifications for headgear designed to address specific concerns about individual sports.

Equestrian helmets, designed and built for horseback riders, are tested against an anvil simulating a hoof because a horse’s kick could split a bike helmet apart. White-water helmets have to cushion blows so that the wearers remain conscious and alert, and can swim to safety after a spill. These helmets must drain water as well because a helmet underwater can act like a bucket, dangerously scooping up water and possibly pulling a head back underwater to cause injury.

Headgear for short track speed ice skating presents a different challenge, that of protecting players from others’ skate blades as well as high speed impacts to the ice or walls. ASTM F1849, Specification for Helmets Used in Short Track Speed Ice Skating (Not to Include Hockey), addresses that challenge with a procedure to test the helmet against a skate blade anvil. Pole vaulting standards deal with an altogether different challenge. The helmet’s rear thickness has limits specified in F2400, Specification for Helmets Used in Pole Vaulting, and that helps prevent an athlete’s head from moving forward during the backward landing after a vault.

The soccer environment calls for yet another type of headgear that protects against typical soccer field impacts but permits heading the ball. The tests in ASTM F2439, Specification for Headgear Used in Soccer, are designed to achieve that result. A bicycle helmet contains stiff, crushable foam that permanently deforms to attenuate impact energy while football helmets are multi-impact. This raises an important distinction among helmets — some are designed to withstand thousands of impacts and recover, and others should be replaced after one impact.

Non-Catastrophic Head Injuries

Committee F08 members speak of “tuning” helmets to accommodate the different hazards posed by a spectrum of sports and activities. One of the hazards receiving more attention and research these days is concussion or, more specifically, mild traumatic brain injury.

For centuries there have been academic and popular discussions about the definition of concussion and other brain injuries. Even Hippocrates, of the eponymous medical care oath, is credited with offering an opinion on what constitutes a noteworthy head injury. In the more recent past, the definition of concussion has ranged from mild injury to death.

Recently the MTBI term has begun to be used to refer to less than life-threatening concussion events. MTBI distinguishes the threshold injury from the more immediately life-threatening event. Because they are called “mild” traumatic brain injuries it is easy to think of them as minor, yet they are rarely minor in nature and never minor to the sufferer. Any injury to the brain must be taken seriously.

It is well established that repeated MTBI could cause complications and enduring ramifications. Cumulative symptoms such as irritability, language changes and loss of motor skills may not show up at first injury or for a long time.

Today, F08.53 members are particularly interested in understanding how standards can be established for helmets that would protect against non-catastrophic injury such as MTBI. In the last five years, the amount of research about this has accelerated and there has been much discussion about MTBI.

“It is important to prevent the first MTBI event,” says Halstead. And, regarding the cumulative effect of repeated MTBI, he adds, “if you can prevent another impact and allow the brain time to heal, you can reset the clock, so to speak.” This time for the brain to return to normal function without additional insult may reduce the risk of multiple MTBI events. The challenge is that any helmet meant to manage an MTBI may not be the same helmet that would manage a catastrophic injury.

In American football, catastrophic injuries are now rare, given more than 40 years of research and development and the implementation of standards and rules. Over the last several years, football associations, including the National Football League, have become more interested in studying non-catastrophic injury. Their challenge has been how to measure MTBI in a competitive world where coaches and players may not know when a player has been injured or is reluctant to stay out of the game, or even admit to being injured.

Since 2004, Greenwald has led a research team, including members of Committee F08, to study the effects of football and other head impacts. During practices and games, sensors and a radio link located in the helmet monitor head (not helmet) accelerations in all directions to capture impact location and duration. Both a player’s impact exposure history and impact magnitude history are monitored. This same technique is being used to study the frequency and severity of toddlers’ playground head injuries, according to Greenwald.

The research team has recorded more than one million data points in football and hockey players. “We are looking forward to using the analyzed data to better understand this important injury and to determine how best to incorporate the research into future iterations of ASTM standards,” says Greenwald. Once a g level can be established that is closely related to the incidence of MTBI diagnosis, an appropriate helmet test can be developed for use across laboratories. It is important not to jump the gun, according to Greenwald. “We have to make it open for debate. We need the research data to support the standard.”

Participation Welcome

Subcommittee F08.53 welcomes participation in the ongoing review of its standards and its two proposed new standards on helmets for nonmotorized recreational water sports and labeling headgear.

For more information, please contact David Halstead, Southern Impact Research Center (phone: 865-523-1662) or Christine Sierk, ASTM (phone: 610-832-9728).


Andrea Smith has spent more than 15 years as a public relations writer for academic medical centers. She has also been a newspaper and magazine writer and editor. She holds a B.A. in English from Barnard College and lives in Devon, Pa.