Michael Carhart

Head injury in snowboarding: evaluating the protective role of helmets

According to a 1999 report by the U.S. Consumer Product Safety Commission, head injuries represent approximately 14 % of all skiing and snowboarding injuries. In a recent retrospective study of patients treated for snowboarding-related head injuries, Nakaguchi and Tsutsumi (2002) found that major head injuries were most often associated with backward falls (68 %) resulting in occipital impacts (66 % of falls) occurring on a gentle or moderate slope. They concluded that the majority of severe snowboarding head injuries were caused by the “opposite-edge phenomenon” where the snowboarder falls backward and contacts the occiput. In order to determine if the use of skiing helmets would reduce the likelihood of head injury associated with catching an edge snowboarding, we conducted a two-part study. In the first part, we measured the speeds of over 180 snowboarders on beginner and intermediate slopes at Mammoth, CA. Across all locations at the resort, the average speeds of beginner and intermediate snowboarders were 17.7 kph (11.0 mph) and 31.9 kph (19.8 mph), respectively. In the second part of the study, we used an instrumented 50th percentile male Hybrid III anthropomorphic test device (ATD) to determine the head accelerations and neck loads associated with a backward fall onto the occiput, both with and without wearing a helmet. For these tests, the ATD was fitted with snowboarding equipment and accelerated to the speeds associated with an intermediate snowboarder (as measured in the first part of the study). Once the ATD was at speed, the snowboard was snubbed on the back edge, simulating the “opposite-edge phenomena” and the posterior aspect of the ATD head was propelled toward the snow surface or a simulated tree. Film analysis of the ATD fall kinematics demonstrated a rapid transition to whole-body angular motion at opposite edge catch. The use of a helmet reduced substantially the linear accelerations and head injury criterion associated with head-to-ground contact on hard, icy snow and during the simulated tree contact. Also, the neck loads were reduced modestly with helmet use. These findings indicate that helmets can mitigate head-to-ground contact severity associated with a common snowboarding fall scenario, the “opposite-edge-phenomenon.”

Electromyographic activity and posturing of the human neck during rollover tests

Lateral head motions, torso motions, lateral neck bending angles, and electromyographic (EMG) activity patterns of five human volunteer passengers are compared to lateral motions of a Hybrid III ATD during right-left and left-right fishhook steering maneuvers leading to vehicular tip-up. While the ATD maintained relatively fixed lateral neck angles, live subjects leaned their heads slightly inward and actively utilized their neck musculature to stiffen their necks against the lateral inertial loads. Except for differences in neck lateral bending, the Hybrid III ATD reasonably reflects occupant kinematics during the pre-trip phase of on-road rollovers.

Evaluation of Human Surrogate Models for Rollover

Anthropomorphic test dummies (ATDs) have been validated for the analysis of various types of automobile collisions through pendulum, impact, and sled testing. However, analysis of the fidelity of ATDs in rollover collisions has focused primarily on the behavior of the ATD head and neck in axial compression. Only limited work has been performed to evaluate the behavior of different surrogate models for the analysis of occupant motion during rollover. Recently, Moffatt et al. examined head excursions for near- and far-side occupants using a laboratory-based rollover fixture, which rotated the vehicle about a fixed, longitudinal axis. The responses of both Hybrid III ATD and human volunteers were measured. These experimental datasets were used in the present study to evaluate MADYMO ATD and human facet computational models of occupant motion during the airborne phase of rollover. Occupant motion predicted by the Hybrid III ATD computation models provided a good match to the temporal movement patterns and corridors of torso and head excursion measured in the volunteers. Differences in torso and head-neck posture were attributed to active muscle contractions in the volunteers. Simulations performed using the TNO human facet model, in the absence of muscle tone, predicted large head excursions and lateral neck and torso bending. These findings were attributed to the stiffer Hybrid III ATD neck and torso as compared to the spinal model incorporated in the human facet model. Although it is possible to model active muscle forces using the TNO human facet model, the appropriate control schemes for coordinating muscle activity in the rollover environment have not been established. Without the implementation of appropriate muscular controls, the TNO human model appears to be best suited to high-force environments or low-force environments where the occupant is unconscious or incapacitated. Our results indicate that among the currently available human computational surrogate models, the Hybrid III ATD provides the best prediction of occupant motion when compared to the available human volunteer data. These results have provided us the impetus to study future human models that incorporate active muscle control.

Development of a computational method to predict occupant motions and neck loads during rollovers

The mechanics of on-road, friction-induced rollovers were studied with the aid of a three-dimensional computer code specifically derived for this purpose. Motions of the wheels, vehicle body, occupant torso, and head were computed. Kanes method was utilized to develop the dynamic equations of motion in closed form. On-road rollover kinematics were compared to a dolly-type rollover at lesser initial speed, but generating a similar roll rotation rate. The simulated on-road rollover created a roof impact on the leading (drivers) side, while the dolly rollover simulation created a trailing-side roof impact. No head-to-roof contacts were predicted in either simulation. The first roof contact during the dolly-type roll generated greater neck loads in lateral bending than the on-road rollover. This work is considered to be the first step in developing a combined vehicle and occupant computational model for studying injury potential during rollovers.

Seat Belt Restraint Evidence Generated in the Presence of Fractured Glass

Physical evidence on the seat belt restraint system is one source of data used by investigators to determine whether or not an occupant was wearing their seat belt during a crash. Evidence of occupant loading on seat belts generated during crash events has been thoroughly researched and is well documented in the literature. However, there is a paucity of data regarding the physical evidence produced when fractured glass is introduced into the restraint system during occupant loading events. The objective of this study is to characterize the physical evidence generated by glass-to-seat belt interaction during low-level impact loading, and compare this evidence with the types of seat belt marks that can be generated inadvertently by accident scene bystanders, emergency responders, and crash investigators. The presence of glass particles in and around the vehicle at the end of a crash event may contribute to the inadvertent generation of physical evidence. Movable side windows composed of tempered safety glass and laminated safety glass were fractured via impactor loading representative of occupant impact. The resulting glass fracture fragments were separated by size using a series of sieves, and the distribution of glass fragments size was quantified. New service-replacement seat belt retractor assemblies (including D-ring, latch plate, anchor, and webbing) were tested using a Seat Belt Load Simulator (SBLS) fixture, which simulates occupant loading by applying a repeatable load pulse to the restraint system. Each retractor assembly was mounted onto the SBLS fixture in a position representative of belt routing when installed in a vehicle. A repeatable lap-shoulder belt stroke pulse, representative of low-level restraint loading and consistent in magnitude and duration with loads produced during rollover, was applied using the SBLS with glass fragments of varying sizes introduced onto the webbing surface adjacent to the D-ring and latch plate surfaces. Additional test series were run to investigate the types of physical evidence generated in the presence of glass under non-crash loading scenarios. These scenarios included the extraction of webbing with glass fragments present adjacent to the D-ring and latch plate, extraction of webbing over glass fragments captured or fixed in a window seal, and the compression of webbing with various sizes of glass fragments interposed between the webbing and a reaction surface. Documentation of each restraint system was performed post-test. Seat belt loading events that occurred in the presence of fractured safety glass produced characteristic markings on the restraint system hardware and webbing. The tests conducted to examine non-crash loading evidence generated in the presence of fractured safety glass revealed markings on the restraint system that differed from those generated in a simulated loading event. Language: en