Dennis V. Andrzejak

MECHANISM OF INJURY FROM AIR BAG DEPLOYMENT LOADS

Loadings induced by deploying currently representative air bags were studied with driver surrogates (anesthetized swine) leaning against the system during inflation. Torso injury mechanisms were studied in a physiologic model, supported against a static steering wheel-mounted air bag system. Severe and extensive chest and abdominal injuries to the swine were observed in the tests. Loading caused by air bag deployment can occur in either of two phases. The first phase represents the initial punch out of the bag from the module; the second phase represents the membrane force of the inflating bag. Statistical analysis indicated that punch out induced injury because of the high rate of loading to the surrogate body region in direct contact with the air bag module. Membrane forces induced injury by high compression over a larger area. Punch-out loading might be reduced by allowing the bag to escape from other parts of the container not in contact with the driver during deployment. Loading by the inflating bag might be reduced by using a compliant steering system to support the module. The amount and rate of generated gas had only marginal effect on the cumulative injury. Even an inflator with inadequate gas output to protect a properly seated occupant had sufficient energy to induce severe injuries in a surrogate in contact with the inflating module. Analysis of the field relevance of the results must consider not only the injury potential given that a driver is in direct contact with the air bag module at the time of deployment, but also the expected field frequency of such an event. Analysis of the field relevance of the results must also consider the correlation of the laboratory test environment with real-world exposure.

Biomechanics of Liver Injury by Steering Wheel Loading

Abdominal injury induced by steering wheel contact at a velocity of 32 km/hr was investigated using anesthetized swine as the surrogate on a Hyge sled. The lower rim of the wheel was positioned 5 cm below the xyphoid. By varying wheel stiffness, wheel orientation, and column angle, resultant abdominal injury ranged from fatal or critical to minor or none. Wheel stiffness was found to be the primary determinant of abdominal injury severity. The mechanism of abdominal injury was identified to be the rim impacting the abdomen and exceeding a combined velocity and compression sensitive tolerance limit. Abdominal injury occurred within the initial 15 ms of wheel contact before whole body movement of the surrogate of column compression, which were initiated by hub contact with the thorax. The severity of abdominal injury correlated with the peak viscous response which can be represented by the product of the instantaneous velocity of abdominal deformation and abdominal compression. It did not correlate with spinal acceleration.

BIOMECHANICS OF INJURY IN LATERAL IMPACTS

Fourteen anesthetized swine were subjected to blunt lateral impact at velocities of 4.3, 6.7, or 8.2 m/s with a 15 cm flat pendulum weighing 23.4 kg accelerated to impact speed by a power-assisted pneumatic impactor. Injuries consisted of laceration of the liver and spleen resulting in severe hemoperitoneum and death by ventricular fibrillation and respiratory arrest in the highest severity impacts. Logist analysis of the biomechanical responses and serious or fatal injury indicated that the maximum Viscous response (VC) had the best correlation with injury risk. A tolerance level of VC = 0.89 m/s was determined for a 25% probability of serious injury. In contrast, maximum chest compression did not correlate with injury. The experiments indicate that internal organ and soft tissue injury may occur by a Viscous mechanism during the rapid phase of compression of the body. The Viscous response is an effective measure of injury risk in side impacts.

An Analysis of Preventive Methods for Baseball-Induced, Chest Impact Injuries

The purpose of this study was to evaluate a nonliving laboratory model for the low-mass, high-velocity chest impact scenario associated with baseball impact deaths in children. A second purpose was to evaluate current protective sports equipment that could favorably modify the incidence of chest imp

Analysis and Comparison of Head Impacts Using Baseballs of Various Hardness and a Hybrid III Dummy

The use of batting helmets in baseball has substantially reduced the incidence of head injuries, and softer baseballs have been developed to further reduce the risk of injury for an unprotected head. This study utilized a 5th-percentile Hybrid III female dummy, which is similar in size to a 10–12-year-old child, to evaluate the effectiveness of various softer baseballs. A pneumatic gun accelerated the balls to a speed of 60 mi/h (27 m/s). Head impacts were delivered frontally on the forehead or between the eyes and laterally on the temple. Peak resultant head acceleration and head injury criterion (HIC) were significantly lower with the softer baseballs. Using logist analysis of the forehead HICs, the risk of head injury was 20% with an official hardball versus 12–16% with softer baseballs, a 4–8% lower increment in injury risk. The risk of injury was higher using head acceleration and for the temple impacts; however, the range in effectiveness of the softer baseballs is smaller than predicted from the National Operating Committee on Standards for Athletic Equipment (NOCSAE) test procedure. Since the NOCSAE procedure was developed for helmeted impacts, there may be a lack of biofidelity for unprotected head impacts. The force of impact was 2.5–18.0 kN and was significantly lower with the softer baseballs. The results of this study indicate that the softer baseballs reduce the risk of head injury, but not to the degree previously claimed. Additional work is needed to determine the actual range of effectiveness in preventing sport-related injuries in children.

BIOMECHANICS OF ABDOMINAL INJURIES BY ARMREST LOADING

Anesthetized pigs were exposed to impact against a padded side interior that included an armrest with either a SOFT or STIFF crush characteristic. The purpose was to assess liver and spleen injury under specific impact conditions. The STIFF armrest resulted in severe abdominal and thoracic injury in five side-impact animal tests. Injuries of the liver and spleen included deep lacerations, tears of major hepatic arteries and veins, and serious hemoperitoneum. The injuries averaged AIS = 4. In contrast, five animals exposed to the SOFT armrest design experienced injuries of lower severity than any animal in the STIFF armrest exposures (p < 0.005). The average injury was AIS = 2. The STIFF armrest protruded into the abdomen and showed little sign of deformation with abdominal loading. This situation is consistent with the occurrence of lacerations at hepatic junctions and between lobes, and displaced rib fractures in several cases. The SOFT armrests crushed fully in each test, indicating that abdominal compression was lower and was limited by armrest deformation.