KOROYD_HELMET SAFETY INITIATIVE
WORKING TOWARDS LESS THAN 5% RISKS
IS YOUR HELMET PROTECTING ANY BETTER THAN 20 YEARS AGO?
The dangers of old safety standards.
Among injured cyclists, head injuries account for approximately two thirds of hospital admissions and three-quarters of fatal injuries. Helmets reduce the probability and the severity of skull fractures and traumatic brain injuries as a result from deceleration of the head.
Many helmet safety standards were issued about 20 years ago and still have the same limitations in maximum deceleration. While the automotive industry advanced the safety of cars continuously for decades, sports markets clearly need to catch up.
CYCLING INJURIES IN 2010
FATAL INJURIES IN EUROPE
HEAD INJURIES / HOSPITAL ADMISSION : 66% HEAD INJURIES / CYLCING FATALITY : 75%
All helmets have to meet safety standards that are set by governments. The safety standards are designed to mimic actual head impacts by dropping a headform with a helmet with a certain velocity onto an anvil. The maximum deceleration is measured and has to be below the standard’s limit, which is typically between 250 and 300 g in the international safety standards.
SO HOW MUCH DECELERATION CAN YOUR SKULL OR BRAIN REALLY TAKE?
RISK OF HEAD INJURY
The maximum allowed values in many helmet safety standards correlate with a high probability of suffering severe head injuries. The correlated risk of suffering a skull fracture can be as high as 40% when a rider wears a European certified bicycle helmet and impacts the helmet at the reference velocity of 19.5 km/h or 12.1 mph. That risk may increase up to 79% for helmets tested to the US bicycle helmet safety standard at the higher reference impact velocity of 22.3 km/h or 13.9 mph. And at a reference velocity of 27 km/h or 17 mph, a certified European motorcycle helmet is allowed to comply with limits that correlate with a shocking 97% risk of suffering a severe traumatic brain injury and a 77% risk that the injury is fatal. The risk assertions are based on the Prasad/Mertz head injury risk curves that are used in the automotive industry to evaluate acceptance criteria for several tests in NCAP programs around the world.
The probability of suffering a skull fracture correlates with the maximum deceleration of the head during an impact.
In the European and American safety standards the maximum allowed values are 250g and 300g respectively. At 250g the correlated risk of suffering a skull fracture is 40% and at 300g that risk almost doubles to 79%.
TRAUMATIC BRAIN INJURY
Some impacts last longer than others and to evaluate the total energy transferred to your brain during an impact a metric called the Head Injury Criterion or HIC was developed. Research from the car industry has shown that HIC correlates with the risk of suffering severe traumatic brain injuries.
Shockingly, the maximum allowed HIC value for European motorcycle helmets is 2400, which correlated to :
A RISK OF SUFFERING A SEVERE TRAUMATIC BRAIN INJURY OF 97 % A RISK OF SUFFERING A FATAL TRAUMATIC BRAIN INJURY OF 77 %
HOW DO YOU FEEL ABOUT THE CURRENT LIMITS ALLOWED IN THE HELMET SAFETY STANDARDS?
KOROYD VOLUNTARY LOWER LIMITS
HELMETS NEED TO ABSORB MORE ENERGY.
Helmets that comply with lower limits for maximum deceleration and HIC will reduce the risk on these severe head injuries significantly. To determine how much better they should perform, we reviewed the risk curves once again. The automotive industry works towards less than 5% risk targets for skull fractures and severe traumatic brain injuries. When helmets comply with a limit of 183 g for maximum deceleration and a maximum HIC value of 1666, both the risk of suffering a skull fracture and the risk of suffering a fatal traumatic brain injury are reduced to less than 5%. The 5% only applies to the reference impact velocities and test conditions, as the helmet is not designed to absorb impacts for instance with far higher impact velocities
Complying with lower limits to achieve less than 5% risks.
To pass voluntary lower limits, helmets either need more energy absorption material or a better performing energy absorber. Fortunately, technology has progressed.
MAXIMUM CORRELATED RISK OF A SKULL FRACTURE*
MAXIMUM CORRELATED RISK OF A FATAL TRAUMATIC BRAIN INJURY*
* when impacted under the same conditions as described in
the helmet safety standard. Correlated risks are averages
and based on the Prasad/Mertz head injury risk curves.
ADVANCED NEXT GENERATION HELMETS
KOROYD CORES OFFER NEXT GENERATION IMPACT PERFORMANCE
Honeycombs are generally regarded as outstanding impact absorption cores with very linear impact performance and hardly any negative rebound effect. The Koroyd thermoplastic tubular honeycomb core has proven to outperform EPS as an absorption liner material inside protective helmets, with maximum deceleration values often 25% to 35% lower than EPS and HIC values up to 58% lower than EPS with the same liner thickness. With Koroyd absorption liners, bicycle, snow and motorcycle helmets can already pass the limits that correlate with a less than 5% risk of suffering a skull fracture or fatal traumatic brain injury, without increasing the size of the helmet.
REDUCING THE SEVERITY OF INJURIES AND SAVING MANY LIVES
Next generation helmets, with significantly improved energy absorption capabilities will reduce the severity of head injuries and save many lives. The approach of the voluntary lower limits of this helmet safety initiative is endorsed by Dr. Prasad, one of the original developers of the head injury risk curves for the automotive industry.
As safety standards are unlikely to change in the next years to come, it’s up to helmet manufacturers to step up and build these helmets. At Koroyd, we’d love to help.
In this graph here you see the deceleration graph of a high-end EPS based motorcycle helmet. This impact led to a maximum deceleration of 185 g and an HIC of 1838. We then replaced the EPS with our Koroyd core in a second helmet and managed to reduce the maximum deceleration to 126 g and the HIC to 768. The correlated risk of suffering a skull fracture was reduced to < 1% while the correlated risk of fatal traumatic brain injury was reduced from 77% to almost non existing for this impact.
BETTER PROTECTING HELMETS
Helmets reduce the probability and severity of skull fractures and traumatic brain injuries as a result from sudden deceleration of the head.
We are dedicated to creating better helmets. Helmets that are lighter, more durable, more breathable, more sustainable – but foremost – THAT PROTECT BETTER.
TRIED, TESTED AND TESTED AGAIN
Koroyd equipped helmets can already comply with the lower limits that correlate with a less than 5% risk* of suffering a skull fracture and less than 5% risk* of suffering a fatal traumatic brain injury in bicycle, ski and motorcycle markets.
* When impacted under the same conditions as described in the helmet safety standard. Correlated risks are averages and based on the Prasad/Mertz head injury risk curves.
“Its time to re-evaluate the helmet standard and put it at a level where the technology can allow.
I’ve spent over 40 years analysing automotive accident data and developing safety systems. I developed these risk curves together with Dr Mertz to evaluate the likelihood of someone suffering severe head injuries like a skull fracture or traumatic brain injury.
The curves have been used by the US department of transportation to set acceptance criteria for head injuries in several crash standards. They are also used in car safety program around the world and have also been re-validated recently. The HIC limit of 2400 in the motorcycle helmet is way too high. If a pedestrian is hit by a car we allow a maximum HIC of 1000. If the same person falls off his bike HIC 2400 is allowed. It just doesn’t make sense and worse of all it leads to too many severe head injuries and fatalities.
Hopefully one day the risks of suffering severe head injuries in various sports activities can be as low as when driving a car. Till that time this helmet safety initiative with these voluntary lower limits for deceleration and HIC is a major step in the right direction that will improve rider safety very significantly.
It’s been over 20 years that many of these standards have been put in place. Its time to re-evaluate the helmet standard and put it at a level where the technology
Dr. PRIYA PRASAD
“Koroyd is the only material that has been specifically engineered to significantly improve energy absorption and hence helmet safety.
Improving helmet safety is about how well you can manage the impact energy.
This usually means increasing the amount of energy absorbing material used in the helmet or using materials that are more efficient when absorbing energy.
Traditional materials have been empirically derived from those used in the pacakging industry and the helmet safety standards reflect this.
Koroyd is the only material that has been specifically engineered to significantly improve energy absorption and hence helmet safety.”
PETER SAJIC M.Sc
RESEARCH PAPERS ON HEAD INJURY RISK CURVES
The development of the Head Injury Risk Curve (HIRC) and the Skull Fracture Risk Curves (SFRC) that were proposed by Prasad and Mertz m for the adult driving population are reviewed, and the problem with using the Maximum Likelihood method to analyze the cadaver 15ms HIC data is discussed. The cadaver data base for skull fracture is expanded by including non-fracture 15ms HIC values for a number of cadavers which had skull fractures at higher impact severities and by including cadaver test results of Ono and Tarriere. This expanded data set was analyzed using the Mertz/Weber method and a new method called “Certainty Grouping”. An updated version of the Skull Fracture Risk Curve (SFRC) is proposed. The efficacy of this revised curve is demonstrated by comparing its predictions to the results of simulated fracture impacts using a finite element model of the head. The HIRC was not changed since no additional brain damage data were analyzed. The efficacy of the HIRC is demonstrated by comparing its predictions of head injury reductions due to the introduction of airbags and due to improvements in football helmets. The cadaver data of Nusholtz and Stalnaker were added to the expanded cadaver skull fracture data. These data were analyzed to determine the relationship between peak resultant head acceleration and the risk of skull fracture. For equal risk of skull fracture. the 15ms HIC criterion is more discerning because it is time dependent.
An evaluation of the four injury risk curves proposed in the NHTSA NCAP for estimating the risk of AIS>= 3 injuries to the head, neck, chest and AIS>=2 injury to the Knee-Thigh-Hip (KTH) complex has been conducted. The predicted injury risk to the four body regions based on driver dummy responses in over 300 frontal NCAP tests were compared against those to drivers involved in real-world crashes of similar severity as represented in the NASS. The results of the study show that the predicted injury risks to the head and chest were slightly below those in NASS, and the predicted risk for the knee-thigh-hip complex was substantially below that observed in the NASS. The predicted risk for the neck by the Nij curve was greater than the observed risk in NASS by an order of magnitude due to the Nij risk curve predicting a non-zero risk when Nij = 0. An alternative and published Nte risk curve produced a risk estimate consistent with the NASS estimate of neck injury. Similarly, an alternative and published chest injury risk curve produced a risk estimate that was within the bounds of the NASS estimates. No published risk curve for femur compressive load could be found that would give risk estimates consistent with the range of the NASS estimates. Additional work on developing a femur compressive load risk curve is recommended.
In 1983, General Motors Corporation (GM) petitioned the National Highway Traffic Safety Administration (NHTSA) to allow the use of the biofidelic Hybrid III midsize adult male dummy as an alternate test device for FMVSS 208 compliance testing of frontal impact, passive restraint systems. To support their petition, GM made public to the international automotive community the limit values that they imposed on the Hybrid III measurements, which were called Injury Assessment Reference Values (IARVs). During the past 20 years, these IARVs have been updated based on relevant biomechanical studies that have been published and scaled to provide IARVs for the Hybrid III and CRABI families of frontal impact dummies. Limit values have also been developed for the biofidelic side impact dummies, BioSID, EuroSID2 and SID-IIs. The purpose of this paper is to provide in a single document: 1) a listing of the IARVs for measurements made with the Hybrid III and CRABI families of frontal impact dummies, and for the biofidelic side impact dummies, 2) the biomechanical and/or scaling bases for these IARVs, and 3) a comparison of IARVs and regulatory compliance limits and how they affect restraint design.
The development of the Head Injury Risk Curve (HIRC) and the Skull Fracture Risk Curves (SFRC) that were proposed by Prasad and Mertz for the adult driving population are reviewed, and the problem with using the Maximum Likelihood method to analyze the cadaver 15ms HIC data is discussed. The cadaver data base for skull fracture is expanded by including non-fracture 15ms HIC values for a number of cadavers which had skull fractures at higher impact severities and by including cadaver test results of Ono and Tarriere. This expanded data set was analyzed using the Mertz/Weber method and a new method called “Certainty Grouping”. An updated version of the Skull Fracture Risk Curve (SFRC) is proposed. The efficacy of this revised curve is demonstrated by comparing its predictions to the results of simulated fracture impacts using a finite element model of the head. The HIRC was not changed since no additional brain damage data were analyzed. The efficacy of the HIRC is demonstrated by comparing its predictions of head injury reductions due to the introduction of airbags and due to improvements in football helmets. The cadaver data of Nusholtz and Stalnaker were added to the expanded cadaver skull fracture data. These data were analyzed to determine the relationship between peak resultant head acceleration and the risk of skull fracture. For equal risk of skull fracture, the 15ms HIC criterion is more discerning because it is time dependent.
A review and analysis of existing cadaver head impact data has been conducted in this paper. The association of the Head Injury Criterion with experimental cadaver skull fracture and brain damage has been investigated, and risk curves of HIC versus skull fracture and brain damage have been developed. Limitation of the search for the maximum HIC duration to 15ms has been recommended for the proper use of HIC in the automotive crash environment.
The COST 327 action was established with seven research topics, with a timetable and four main onjectives, all to be achived using a wide range of European experience to determine or modify national approaches.
- Literature review
- Accident data collection
- Headform assessment
- Reconstruction of helmet accident damage
- Mathematical model of the skull, brain, neck, and helmet
- Human tolerance to injury
- Development of test procedures
- The first was to establish the distribution and severity of injuries experienced by motorcyclists, concentrating on the head and neck.
- The second was to determine the most significant head and neck injury mechanisms.
- Thirdly, the tolerance of the human head, brain and neck to these injuries and injury
mechanisms was to be established.
- The overall findings were to be used to propose a specification for future testing of motorcycle helmets in Europe.
All risk assertions in the initiative have been made using the Prasad/Mertz head injury risk curves. The risk curves cannot accurately predict the risk of injury from an impact. Actual risk of injury will vary from person to person and depends on many factors, including but not limited to the impact velocity, the angle of the impact, the impact surface, as well as the age, weight and physical condition of the rider.
The correlated risk of suffering a skull fracture or fatal traumatic brain injury is reduced to less than 5% according to the Prasad/Mertz risk curves for impacts with a maximum deceleration of 183 g and maximum HIC value of 1666.
No helmet can protect riders from any and all injuries.
When riding, please wear a helmet.
INNOVATION. IN EVERYTHING WE DO.
SAFETY INITIATIVE DISCUSSION.