The impact response of traditional and BMX-style bicycle helmets at different impact severities

Bicycle helmets reduce the frequency and severity of severe to fatal head and brain injuries in bicycle crashes. Our goal here was to measure the impact attenuation performance of common bicycle helmets over a range of impact speeds. We performed 127 drop tests using 13 different bicycle helmet models (6 traditional style helmets and 7 BMX-style helmets) at impact speeds ranging from 1 to 10 m/s onto a flat anvil. Helmets were struck on their left front and/or right front areas, a common impact location that was at or just below the test line of most bicycle helmet standards. All but one of the 10 certified helmet models remained below the 300 g level at an impact speed of 6 m/s, whereas none of the 3 uncertified helmets met this criterion. We found that the helmets with expanded polystyrene liners performed similarly and universally well. The single certified helmet with a polyurethane liner performed below the level expected by the Consumer Product Safety Commission (CPSC) standard at our impact location and the helmet structure failed during one of two supplemental tests of this helmet above the test line. Overall, we found that increased liner thickness generally reduced peak headform acceleration, particularly at higher impact speeds.     

The protective performance of bicyclists' helmets in accidents

A study of the injuries sustained by 1,892 bicycle riders during accidents indicated that 432 of the bicyclists had been wearing a helmet and 64 of the latter group had sustained an impact to the helmet. The 64 helmets were evaluated in this project to relate the nature and severity of the impact they had sustained to the head injury experienced by the wearer. The protective performance of the helmet shells, impact absorbing liners, and retention systems were evaluated, and the severity of the impacts sustained by the helmets was simulated in the test laboratory. The simulation was performed by dropping sample helmets from progressively greater heights in a test apparatus until the damage observed on a sample helmet matched that observed on an accident damaged helmet. The severity observed in the simulated impacts was compared with the severity of test impacts prescribed in established helmet performance standards (ANSI 1984; Snell 1984; AS 1986). It was found that all of the impacts occurred against flat objects; a high proportion of helmets sustained more than one impact; most impacts occurred on areas of a helmet which were not tested during certification to a standard; and many impacts were more severe than those stipulated in performance standards. The predominant form of head injury recorded was low severity concussion--AIS-1, AIS-2, AIS-3. All serious head injuries occurred when the helmet came off the rider's head and collapsed due to a material defect or was struck predominantly below the rim. A high proportion of helmets worn by young riders had been misused, and many helmets displayed defects in the impact-absorbing liners. Recommendations have been made for improving helmet construction and altering current standards to reflect the conditions encountered in the field.     

The impact response of motorcycle helmets at different impact severities

Helmets reduce the frequency and severity of head and brain injuries over a range of impact severities broader than those covered by the impact attenuation standards. Our goal was to document the impact attenuation performance of common helmet types over a wide range of impact speeds. Sixty-five drop tests were performed against the side of 10 different helmets onto a flat anvil at impact speeds of 0.9–10.1 m/s (energy = 2–260 J; equivalent drop heights of 0.04–5.2 m). Three non-approved beanie helmets performed poorly, with the worst helmet reaching a peak headform acceleration of 852g at 29 J. Three full-face and one open-face helmet responded similarly from about 100g at 30 J to between 292g and 344g at 256–260 J. Three shorty style helmets responded like the full-face helmets up to 150 J, above which varying degrees of foam densification appeared to occur. Impact restitution values varied from 0.19 to 0.46. A three-parameter model successfully captured the plateau and densification responses exhibited by the various helmets (R² = 0.95–0.99). Helmet responses varied with foam thickness, foam material and possibly shell material, with the largest response differences consistent with either the presence/absence of a foam liner or the densification of the foam liner.     

Optimization of the Chin Bar of a Composite-Shell Helmet to Mitigate the Upper Neck Force

The chin bar of motorcycle full-face helmets is the most likely region of the helmet to sustain impacts during accidents, with a large percentage of these impacts leading to basilar skull fracture. Currently, helmet chin bars are designed to mitigate the peak acceleration at the centre of gravity of isolated headforms, as required by standards, but they are not designed to mitigate the neck force, which is probably the cause of basilar skull fracture, a type of head injury that can lead to fatalities. Here we test whether it is possible to increase the protection of helmet chin bars while meeting standard requirements. Fibre-reinforced composite shells are commonly used in helmets due to their lightweight and energy absorption characteristics. We optimize the ply orientation of a chin bar made of fibre-reinforced composite layers for reduction of the neck force in a dummy model using a computational approach. We use the finite element model of a human head/neck surrogate and measure the neck axial force, which has been shown to be correlated with the risk of basilar skull fracture. The results show that by varying the orientation of the chin bar plies, thus keeping the helmet mass constant, the neck axial force can be reduced by approximately 30% while ensuring that the helmet complies with the impact attenuation requirements prescribed in helmet standards.     

Evaluation and replication of impact damage to bicycle helmets

A group of 72 impacted bicycle helmets were collected, primarily from manufacturers with a crash replacement policy that encourages the return of damaged helmets. Each damaged helmet was thoroughly inspected and measured to determine the construction details and collision damage. Laboratory replication tests were then performed on selected samples using exemplar helmets to determine impact velocity and peak headform aceleration. The predominant impact location was the front left quarter and the replication studies indicate that the majority of impacts took place on flat surfáces from drop heights of 1 meter or less. Overall, it is evident that a large number of bicycle helmet users who have benefited from the use of a bicycle helmet, and future bicycle helmet standards must incorporate the protective requirements of this unique group.     

The protective effect of a helmet in three bicycle accidents—A finite element study

There is some controversy regarding the effectiveness of helmets in preventing head injuries among cyclists. Epidemiological, experimental and computer simulation studies have suggested that helmets do indeed have a protective effect, whereas other studies based on epidemiological data have argued that there is no evidence that the helmet protects the brain. The objective of this study was to evaluate the protective effect of a helmet in single bicycle accident reconstructions using detailed finite element simulations.Strain in the brain tissue, which is associated with brain injuries, was reduced by up to 43% for the accident cases studied when a helmet was included. This resulted in a reduction of the risk of concussion of up to 54%. The stress to the skull bone went from fracture level of 80 MPa down to 13–16 MPa when a helmet was included and the skull fracture risk was reduced by up to 98% based on linear acceleration. Even with a 10% increased riding velocity for the helmeted impacts, to take into account possible increased risk taking, the risk of concussion was still reduced by up to 46% when compared with the unhelmeted impacts with original velocity. The results of this study show that the brain injury risk and risk of skull fracture could have been reduced in these three cases if a helmet had been worn.     

New composite liners for energy absorption purposes

This work studies the capacity of cork to act as material for the absorption of impact energy. Focus is given on the viability of hybrid paddings consisting of micro-agglomerate cork (MAC) and expanded polystyrene (EPS) through simulations of multi-impacts. EPS is a widely used material for energy absorption applications. However, once deformed, it shows no springback, which means that its capacity for energy absorption is greatly reduced after the first impact. On the other hand, cork is a viscoelastic material that has a good level of energy absorption capacity with almost total springback. An example in which EPS is commonly used is motorcycle helmet liners. In the first part of this work, a compression test is used to assess the effectiveness of the material laws chosen to model the cellular materials under study. Results show that the constitutive laws employed for EPS and micro-agglomerate cork adequately model the actual behaviour in springback absence. In the second part of this work, it was developed a simplified model of a road helmet energy absorption liner. This representative padding was subjected to double impacts as specified in an international helmet standard. The work also studies the use of MAC and EPS arrangements on the energy absorption linear through various configurations. Results were obtained with regard to the head centre of gravity acceleration, final padding thickness and the final weight of a helmet. Conclusions are drawn about the best configuration for the application under study.     

Angular Impact Mitigation system for bicycle helmets to reduce head acceleration and risk of traumatic brain injury

Angular acceleration of the head is a known cause of traumatic brain injury (TBI), but contemporary bicycle helmets lack dedicated mechanisms to mitigate angular acceleration. A novel Angular Impact Mitigation (AIM) system for bicycle helmets has been developed that employs an elastically suspended aluminum honeycomb liner to absorb linear acceleration in normal impacts as well as angular acceleration in oblique impacts. This study tested bicycle helmets with and without AIM technology to comparatively assess impact mitigation. Normal impact tests were performed to measure linear head acceleration. Oblique impact tests were performed to measure angular head acceleration and neck loading. Furthermore, acceleration histories of oblique impacts were analyzed in a computational head model to predict the resulting risk of TBI in the form of concussion and diffuse axonal injury (DAI). Compared to standard helmets, AIM helmets resulted in a 14% reduction in peak linear acceleration (p < 0.001), a 34% reduction in peak angular acceleration (p < 0.001), and a 22–32% reduction in neck loading (p < 0.001). Computational results predicted that AIM helmets reduced the risk of concussion and DAI by 27% and 44%, respectively. In conclusion, these results demonstrated that AIM technology could effectively improve impact mitigation compared to a contemporary expanded polystyrene-based bicycle helmet, and may enhance prevention of bicycle-related TBI. Further research is required.     

Effects of the presence of the body in helmet oblique impacts

The oblique impact methods of motorcycle helmet standards prescribe using an isolated headform. However, in accidents the presence of the body may influence impact responses of the head and helmet. In this study, the effects of the presence of the body, in helmet oblique impacts, are investigated. Using the Finite Element method, oblique impacts of a commercially available helmet, coupled with a model of the human body, are simulated. A comparison between full-body impacts and those performed with an isolated headform show that the presence of the body modifies the peak head rotational acceleration by up to 40%. In addition, it has a significant effect on head linear acceleration and the crushing distance of the helmet's liner. To include the effect of the body on head rotational acceleration in headform impacts, modifying inertial properties of the headform is proposed. The modified inertial properties are determined for a severe and frequent impact configuration. The results of helmet impacts obtained by using the modified headform are in very good agreement with those of full-body impacts; this verifies the accuracy of the proposed method.     

FEA of oblique impact tests on a motorcycle helmet

In accidents, motorcycle riders full-face helmets often make oblique impacts with road surfaces. Finite element analysis was used to predict the rotational and linear acceleration of a Hybrid II headform, representing a motorcyclist's head, in such impacts, considering the effects of friction at the head/helmet and helmet/road interfaces. Simulations of the oblique impact test in British Standard BS 6658 were validated by comparison with published data. This showed that COST 327 experimental data was largely determined by the friction coefficient (0.55) between the helmet shell and abrasive paper, and hardly affected by that between the head and helmet. Slip was predicted at the shell/paper interface throughout the impact, due to the high angular inertia of the helmet, and the normal force remaining below 3.5 kN. Simulations of more severe motorcycle helmet impacts explored the effects of impact site and direction, impact velocity components, helmet fit and the scalp. In these impacts, the higher velocity component normal to the road caused high frictional forces on the helmet shell, eventually causing it to roll on the road. The peak headform rotational accelerations, at some impact sites, were potentially injurious. The most effective method of reducing head rotational acceleration could be a reduction in the linear acceleration limit of the helmet standards.     

Finite-element analysis of bicycle helmet oblique impacts

Finite-element analysis (FEA) was performed for bicycle helmets making oblique impacts with a road surface, to evaluate the linear and rotational accelerations of the headform. Helmet rotation on the head was considered, modelling the helmet and retention strap interactions with the headform. The effects of frictional parameters on the response were explored, and parameters selected to reproduce experimental results. Predictions were made for two helmets, for a range of impact locations and tangential velocities. The design method for the peak headform linear acceleration was confirmed; it was hardly affected by the tangential component of the impact velocity. The peak headform rotational acceleration was investigated as a function of the helmet geometry, impact sites and velocities and the contributing mechanisms established.     

佩戴头盔模拟飞行8h的飞行耐力试验

目的:测定飞行员长时间(8h)模拟飞行时,佩戴飞行头盔对其飞行耐力的影响,为飞行头盔设计改进和使用提供依据。方法:按受试者佩戴头盔的重量(1.7 kg与2.0 kg)和任务负荷(仅提供影视音乐节目与模拟航线飞行)的不同将试验分为3组,观察记录受试者的主诉和表现。结果:受试者反映的问题,主要是闷热和压痛。为减轻闷热和压痛,受试者不断地调整头盔。闷热、压痛和调整头盔频次与时间进程相关,闷热出现在1h-3h,压痛出现在4-7h。因头盔重量和任务负荷不同,各组受试者的主诉和调整头盔频次有显著性差异。结论:头盔重量以及任务负荷等对飞行耐受能力有重大影响:头盔增重、任务负荷增加,加快了闷热和压痛的生成。频繁地调整头盔是缓解闷热和压痛的主要行为表现。相关测量结果为飞行头盔设计改进和使用提供了重要依据。     

Parental attitudes and behaviours concerning helmet use in childhood activities: Rural focus group interviews

Previous research demonstrates the importance of parents in ensuring that their children practice proper helmet use. Parents encourage helmet use by setting an example when they wear helmets, as well as establishing rules that the children are expected to follow. Research in the area of helmet use predominantly focuses on bicycle helmets, but there are a number of childhood activities for which a helmet is required. The purpose of this research was to examine rural parents’ attitudes toward helmet use and investigate when, and for what activities, they require their children to wear helmets. Rural parents were selected as there is evidence that helmet use is less frequent among children in rural settings.     

The effect of temperature on the capability of industrial safety helmets to absorb impact energy

The fundamental document specifying the requirements and testing methods applicable to industrial safety helmets in European Union member states is the standard EN 397:2012. According to that standard, one of the most important parameters of a helmet is shock absorption, determined for an impact of a striker with a kinetic energy of 49 J. The shock-absorbing performance of a safety helmet involves absorbing the energy of a striking object associated with a deformation of the shell and cradle, as well as an increase in the force transferred to the user’s head. The paper presents a study conducted with the aim to estimate the actual amount of energy absorbable by various helmet types without exceeding the threshold value of the force acting on the user’s head. A method of testing helmet deformation and the force acting on the helmet during an impact exerted by a falling object is presented. The effect of the temperature used for conditioning various helmet types on their capability to absorb impact energy was determined. The causes of deterioration of that capability due to temperature changes are analyzed for various designs of helmets made of different materials, and possible solutions to that problem are offered.     

Motorcycle helmet use in relation to legal requirements

Helmet use by motorcyclists was observed in late 1978 in cities in six U.S. states with varying legal requirements regarding their use. In two cities (Baltimore, Maryland and Miami, Florida) in which all motorcyclists are legally required to wear helmets, virtually all wore helmets. In three cities (New Orleans, Louisiana, Phoenix, Arizona and Houston, Texas) where helmet use laws requiring use by all motorcyclists were changed in 1976 or 1977 so that use is required only by those less than 18 years old, wearing rates were 39, 46 and 63%, respectively. In Los Angeles, California, which has never had a law requiring helmet use, 46% wore helmets.

Based on these survey results, and on the known efficacy of helmets in reducing injuries to motorcyclists, the repeal of helmet laws that occurred in 26 states in 1976–1978 can be expected to result in major increases in motorcyclist deaths in succeeding years.     

Adult headform impact tests of three Japanese child bicycle helmets into a vehicle

The head is the body region that most frequently incurs fatal and serious injuries of cyclists in collisions against vehicles. Many research studies investigated helmet effectiveness in preventing head injuries using accident data. In this study, the impact attenuation characteristics of three Japanese child bicycle helmets were examined experimentally in impact tests into a concrete surface and a vehicle. A pedestrian adult headform with and without a Japanese child bicycle helmet was dropped onto a concrete surface and then propelled into a vehicle at 35 km/h in various locations such as the bonnet, roof header, windshield and A-pillar. Accelerations were measured and head injury criterion (HIC) calculated. In the drop tests using the adult headform onto a concrete surface from the height of 1.5 m, the HIC for a headform without a child helmet was 6325, and was reduced by around 80% when a child helmet was fitted to the headform. In the impact tests, where the headform was fired into the vehicle at 35 km/h at various locations on a car, the computed acceleration based HIC varied depending on the vehicle impact locations. The HIC was reduced by 10–38% for impacts headforms with a child helmet when the impact was onto a bonnet-top and roof header although the HIC was already less than 1000 in impacts with the headform without a child helmet. Similarly, for impacts into the windshield (where a cyclist’s head is most frequently impacted), the HIC using the adult headform without a child helmet was 122; whereas when the adult headform was used with a child helmet, a higher HIC value of more than 850 was recorded. But again, the HIC values are below 1000. In impacts into the A-pillar, the HIC was 4816 for a headform without a child helmet and was reduced by 18–38% for a headform with a child helmet depending on the type of Japanese child helmet used. The tests demonstrated that Japanese child helmets are effective in reducing accelerations and HIC in a drop test using an adult headform onto a relatively rigid hard surface, i.e., simulating a road surface or concrete path. However, when the impact tests are into softer surfaces, the child helmet’s capacity to decrease accelerations is accordingly reduced. Impacts into the windshield, while below the critical HIC value of 1000, indicated higher HIC values for a headform with a child helmet compared to an adult headform without a child helmet. The unpredictable nature of the results indicates further research work is required to assess how representative the stiffness of an adult headform is when compared to an actual head.     

Exploration of the barriers to bicycle helmet use among 12 and 13 year old children.

Despite the fact that bicycle helmet usage reduces the risk of bicycle-related head injuries, only a small percentage of children routinely wear helmets. The aim of this study was to qualitatively explore the barriers to bicycle helmet usage among 12 and 13 year old children. The study is based on four focus groups with 31 children from schools is an urban New York City area. A majority of both boys and girls did not perceive a need for wearing helmets for routine riding or short trips, and felt that helmet usage was uncomfortable and made them appear dumb. Also, students could not recall any health promotion efforts by a variety of health providers and felt local legislation had little impact on usage rates. The qualitative findings of this study provide valuable material for researchers seeking to understand the factors associated with non-use of bicycle helmets.     

Helmet use and motorcycle fatalities in Taiwan

Motorcycle deaths accounted for more than half of total traffic fatalities in Taiwan in 2002. This study uses the police-reported crash data from Taiwan between 1999 and 2001 to estimate the effectiveness of helmets, simultaneously taking into account of sample selection bias. Sample selection arises because helmet usage will affect the probability of death or injury, which in turn influences whether a crash is included in the data. The results show that sample selection does not seriously bias the estimate of helmet effectiveness and helmets reduce the probability of death in a crash by 40%, which is higher than what was previously found. Without helmets, the number of motorcyclists killed in 2001 would have jumped by 51%. The estimated proportion of helmeted motorcyclists has increased from 71 to 78% between 1999 and 2001, suggesting that helmet use is rising after the implementation of mandatory helmet law in 1997. Also, helmets significantly reduce the likelihood of head and neck injuries in a crash by 53%, and lead to a 71% reduction in the probability of death caused by head and neck injuries.     

Evaluation of head response to ballistic helmet impacts using the finite element method

Injuries to the head caused by ballistic impacts are not well understood. Ballistic helmets provide good protection, but still, injuries to both the skull and brain occur. Today there is a lack of relevant test procedure to evaluate the efficiency of a ballistic helmet. The purpose of this project was (1) to study how different helmet shell stiffness affects the load levels in the human head during an impact, and (2) to study how different impact angles affects the load levels in the human head. A detailed finite element (FE) model of the human head, in combination with an FE model of a ballistic helmet (the US Personal Armour System Ground Troops’ (PASGT) geometry) was used. The head model has previously been validated against several impact tests on cadavers. The helmet model was validated against data from shooting tests. Focus was aimed on getting a realistic response of the coupling between the helmet and the head and not on modeling the helmet in detail. The studied data from the FE simulations were stress in the cranial bone, strain in the brain tissue, pressure in the brain, change in rotational velocity and translational and rotational acceleration. A parametric study was performed to see the influence of a variation in helmet shell stiffness on the outputs from the model. The effect of different impact angles was also studied. Dynamic helmet shell deflections larger than the initial distance between the shell and the skull should be avoided in order to protect the head from the most injurious threat levels. It is more likely that a fracture of the skull bone occurs if the inside of the helmet shell strikes the skull. Oblique ballistic impacts may in some cases cause higher strains in the brain tissue than pure radial ones.     

The prevalence of non-standard helmet use and head injuries among motorcycle riders

OBJECTIVES: This study examined the prevalence of non-standard helmet use among motorcycle riders following introduction of a mandatory helmet use law and the prevalence of head injuries among a sample of non-standard helmet users involved in motorcycle crashes. METHODS: Motorcycle rider observations were conducted at 29 statewide locations in the 2 years following the introduction of the mandatory helmet use law in January, 1992. Medical records of motorcyclists who were injured in 1992 for whom a crash report was available and for whom medical care was administered in one of 28 hospitals were reviewed. Chi-squares and analysis of variance were used to describe differences between groups. RESULTS: Prevalence of non-standard helmet use averaged 10.2%, with a range across observation sites from 0 to 48.0%. Non-standard helmet use varied by type of roadway, day of week, and time of day. Injuries to the head were more frequent and of greater severity among those wearing non-standard helmets than both those wearing no helmet and those wearing standard helmets. CONCLUSIONS: Non-standard helmets appear to offer little head protection during a crash. Future study is needed to understand the dynamics leading to head injury when different types of helmets are worn.