Helmet Standards: What We Need to Make Progress
Summary: This page outlines what we need today to improve helmet standards: scientific underpinnings for standards improvements that can only flow from additional medical research.
First, there are today's constraints:
Injury Mechanism Research
The best known research producing data on the threshold of injury for early helmet standards in the US was collected at Wayne State University beginning in the 1950's from cadaver research. Although studies occasionally appear with newer published data since the Wayne State tolerance curves were developed, bicycle helmet test methods and failure criteria have not been updated in over 40 years.
Dr. George Snively of the Snell Foundation explained to us in 1982 that early research showed that 400 g's meant almost certain permanent injury to the brain, and that he and other writers of the early standards had backed off 25% to provide a margin of safety, arriving at a 300 g pass/fail criterion. At that level he expected the blow to "ring your bell" and cause a concussion, but not cause a catastrophic injury. Although we now know that concussion occurs around 80 to 120 g and death may be associated with 200 g's, we continue to use this criterion in US standards for bike helmets and many other helmets. Some non-US standards have lowered it to 250g, and it would be possible to lower it further with helmets meeting it using only current technology.
A second injury criterion is based on limiting the duration of the high g pulse. Although Wayne State researchers did attempt to also define the effect of high g pulses for different periods, Dr. Voigt Hodgson of Wayne State explained to us in 1989 that he was not confident that the data they had collected on intracranial pressure time tolerance curves really supported the published conclusions. He was confident that the research was accurate on the 400 g criterion. Dr. J.J. Liu of the US Department of Transportation told us in 1989 that the 1974 DOT motorcycle helmet standard, with limits on how long the pulse could stay above a certain level--known as dwell time--was based on Wayne State research. The DOT helmet standard, FMVSS 218, has never been updated, although it is the only current standard that we know of that uses dwell time.
A third injury criterion focuses on the rotational energy in an impact that spins or jerks the head, causing the brain to move violently in the skull. Different parts of the brain have different densities, and upon impact they do not move uniformly together. Further, the brain can rotate in relation to the skull. That is known to strain and break nerves, blood vessels and other brain tissue. Although there are measurements for rotation in radians per second, there is still no generally accepted criterion for the level that produces either catastrophic brain injury or concussion.
It is obvious that the acceleration measured in a test lab drop is not necessarily equal to the acceleration a real head sees in an actual crash of the same distance on the street. Partly for that reason, standards-setters in the US have not made changes in the 300 g failure criterion. To do so, we need to do the science and prove what lower threshold would make sense, and we are not able to make that connection at present.
There is a second thread in the seemingly endless discussion of g thresholds: concussion. The vast majority of consumers assume that a helmet should prevent concussion in even the heaviest hits, and that if the helmet protects against severe blows it must surely be easily protective in lesser ones. But in fact the helmets built to our standards are in many cases too hard to protect against a mild concussion in either a low speed hit where foam fails to crush or a much harder hit where clinically evident permanent injury is avoided, but a lesser concussion still results even though the helmet has not crushed completely and bottomed out.
Despite many symposia on concussions, nobody has a clear definition of the threshold of concussion, or at least a workable new failure threshold that can be applied in lab testing to specify "the concussion helmet." For some sports that require multiple impact helmets, there are standards that result in a softer helmet, but they give up a great deal of performance in higher energy hits, and still use the 300 g pass/fail criterion. Manufacturers insist that with current technology they cannot make the softer helmets meet higher impact performance standards without a major loss of consumer acceptance. We suspect that the threshold should be different for children and probably senior citizens than for others, but we have no data to support a change.
Finally, there is the question of rotational injury. We know it is a problem, and perhaps even the worst villain in concussion. But we don't have generally accepted injury thresholds and lab test equivalents to write into our standards. In fact, most of our labs don't even have the test equipment they would need to begin testing helmets for rotational injury performance. And if they did, we would not know what effect would be produced by the best or worst helmets, or if including a rotational energy management test in the standard would result in fewer injuries. Except for one study that showed that rotational impacts can be thought of as off-center translational impacts, and that reducing translational impacts can reduce rotational forces as well, we have no basis to proceed with a rotational standard. That prevents us from assessing scientifically what the effect would be of making helmets thicker.
On top of the lack of concrete data for insisting on standards improvement, our litigious society has added another constraint. If a manufacturer wants to offer a helmet with superior protection, it must build that same protection into every model in its line or face lawsuits charging that they failed to provide the use the most protective technology possible. And if a manufacturer has a new helmet that is much more protective, their corporate attorneys will not permit it to be advertised as superior in preventing injury because they would anticipate losing every lawsuit involving injuries received in that model. So helmet advertising is an exercise in creativity as marketers try to tout their products while never saying anything about their performance. Only a standards upgrade can lift all boats in this tide.
Faced with these problems, standards makers are finding it difficult to improve the protection required by our standards. We are not making any progress on adding to our testing methodology and not making any changes to lower our failure thresholds. We are not attempting to test consumer acceptance of more protective helmets because we have no benchmark to determine exactly how much more protective the helmets should be, and although manufacturers are actively testing new designs and materials, helmet designers are not being pushed to produce acceptable designs that are larger, heavier or use different technology than the standard plastic-covered EPS or ABS-covered resilient foam that has been the norm for a decade. Coverage requirements for bicycle helmets have actually receded in the ASTM and CPSC standards compared to the 1984 ANSI standard, again with pleas from manufacturers that requiring additional coverage will reduce sales. Snell has held the line and actually increased coverage, but only a tiny fraction of the helmets on the market are certified to their more stringent standard, and most of their certified helmets meet their older 1990 standard instead. The consumer accepts this situation without protest, profit margins are slim with cheap Asian production available everywhere, and although some manufacturers push forward with research on new approaches, funds are generally scarce for research and development of new models that might not sell.
Prescription for Progress
To emerge from the doldrums we need a stimulus that will challenge the status quo. That stimulus will not come from the manufacturers, whose profits are thin and who are convinced that beefing up standards before new technology is developed will require bulkier helmets that consumers will reject.
Progress will not come from consumers, who for the most part do not understand the standards issues and are not overly concerned as a group about what they regard as the details of helmet protection. It will not come from the government, where the industry lead is carefully watched and consumer demand for improved helmets is not being registered.
Progress will not come from government, where the issues are poorly understood and the need for better helmets is not as pressing as other concerns.
Progress in improving helmet standards must come from progress in medical research, pointing the way to a new definition of the protection the wearer really needs. The results must bring out specific criteria that lead to inescapable conclusions on how far helmets must be improved to achieve optimal injury protection. We are encouraged by two developments: a new group began work in 2002 on providing the medical underpinnings for advances in standards based on more accurate injury thresholds. And football players, who suffer more economic loss from concussion than any other population group, are now funding basic research in this field. Results of that research began to become public in 2004, and may someday result in improvements in helmet design, at least for football helmets.
In sum, to make progress toward better helmets:
- We need a better fix on injury thresholds to know how far we should lower the g's in our pass/fail criteria for children, adults and senior citizens.
- We need a better understanding of the injury mechanism usually referred to as rotational acceleration.
- We need an injury threshold for rotational injury, and the research to understand how a helmet design can affect rotational forces in a crash.
- We need more research on how helmet coverage can affect injury rates, and where the test line should be placed to make sure that consumers have the protection they need.
More than a half century has passed since the landmark research at Wayne State produced our first data on g tolerances. The question is, who will produce the "Wayne State Curves" of the 21st century, and when.
Some rays of hope have begun to shine in this gloomy picture. In November of 2002 a group of noted neurological researchers, biomechanicians, finite element modelers and standards writers convened for the first time at the Cleveland Clinic to begin work on developing the research underpinnings to produce the new benchmarks we need, based on scientific assessments of injury thresholds, taking advantage of the research and new techniques now available.
Early in this century the NFL Football Players Association began funding research on concussion in football. Results started appearing in medical journals in 2004. Concussions cost the players millions every year, and the results of the research they are funding have already begun to show up in improved football helmet designs. Perhaps a spillover into designs for other helmets will bring progress in coming years.
A company called Simbex has developed instrumentation to be worn by football players on their heads under their helmets, coupled with data collection on the sidelines. They began monitoring players during games and practices in 2004, and as of 2009 they had collected more than a million data points. Their object is to define the onset of concussion and suggest helmet improvements. Their data show that the task is complex and will take more research.
When US troops began to encounter bomb blasts in Iraq and other countries, the Defense Department and the Vetarans Administration began funding research on the injury mechanism with an eye toward developing more protective helmets to prevent mild traumatic brain injury under combat conditions. The results are likely to improve our understanding of MTBI.
The awareness of the longer term results of concussion, and particularly of repeated concussions, has grown rapidly in the 21st century. The pace of research has acclerated, and interesting results should not be far behind.
This page was last revised on: March 5, 2010.