Occupant Injury and Response on Oblique-Facing Aircraft Seats: A Computational Study.

Increased interest in the airline industry to enhance occupant comfort and maximize seating density has prompted the design and installation of obliquely mounted seats in aircraft. Previous oblique whole-body sled tests demonstrated multiple failures, chiefly distraction-associated spinal injuries under oblique impacts. The present computational study was performed with the rationale to examine how oblique loading induces component level responses and associated injury occurrence. The age-specific human body model (HBM) was simulated for two oblique seating conditions (with and without an armrest). The boundary conditions consisted of a 16 g standard aviation crash pulse, 45 deg seat orientation, and with restrained pelvis and lower extremities. The overall biofidelity rating for both conditions ranged from 0.5 to 0.7. The validated models were then used to investigate the influence of pulse intensity and seat orientation by varying the pulse from 16 g to 8 g and seat orientation from 0 deg to 90 deg. A total of 12 parametric simulations were performed. The pulse intensity simulations suggest that the HBM could tolerate 11.2 g without lumbar spine failure, while the possibility of cervical spine failure reduced with the pulse magnitude <9.6 g pulse. The seat orientation study demonstrated that for all seat angles the HBM predicted failure in the cervical and lumbar regions at 16 g; however, the contribution of the tensile load and lateral and flexion moments varied with respect to the change in seat angle. These preliminary outcomes are anticipated to assist in formulating safety standards and in designing countermeasures for oblique seating configurations.

Influence of bending pre-load on the tensile response of the lumbar spine.

Previous full body cadaver testing has shown that both obliquely oriented seats in survivable aircraft crashes and far-side oblique crashes in vehicles present distinctive occupant kinematics that are not yet well understood. Knowledge surrounding how these loading scenarios affect the lumbar spine is particularly lacking as there exists minimal research concerning oblique loading. The current study was created to evaluate a novel experimental method through comparison with existing literature, and to examine the impact of a static bending pre-load (posture) on the load-displacement response for the whole lumbar spine loaded in non-destructive axial distraction. T12-S1 lumbar spines were tested in tension to 4 mm of displacement while positioned in one of three pre-load postures. These postures were: the spine's natural, unloaded curvature (neutral), flexed forward (flexed), and combined flexion and lateral bending (oblique). Deviations from a neutral spine position were shown to significantly increase peak loads and tensile stiffness. The presence of a flexion pre-load caused statistically significant increases in tensile stiffness, tensile force, and bending moments. The addition of a lateral bending pre-load to an already flexed spine did not significantly alter the tensile response. However, the flexion moment response was significantly affected by the additional postural pre-load. This work indicates that the initial conditions of distraction loading significantly affect lumbar spine load response. Therefore, future testing that seeks to emulate crash dynamics of obliquely seated occupants must account for multi-axis loading.

Responses and Injuries to PMHS in Side-Facing and Oblique Seats in Horizontal Longitudinal Sled Tests per FAA Emergency Landing Conditions.

The objective of the present exploratory study is to understand occupant responses in oblique and side-facing seats in the aviation environment, which are increasingly installed in modern aircrafts. Sled tests were conducted using intact Post Mortem Human Surrogates (PMHS) seated in custom seats approximating standard aircraft geometry. End conditions were selected to represent candidate aviation seat and restraint configurations. Three-dimensional head center-of-gravity linear accelerations, head angular velocities, and linear accelerations of the T1, T6, and T12 spinous processes, and sacrum were obtained. Three-dimensional kinematics relative to the seat were obtained from retroreflective targets attached to the head, T1, T6, T12, and sacrum. All specimens sustained spinal injuries, although variations existed by vertebral level. While the tension mechanism was associated with cervical spine injuries, complex distraction-coupled with bending and tension was attributed to thoracolumbar spine injuries. Skeletal fractures to the ribcage were attributed to compression induced by the restraint from the seatbelt, the presence of the armrest, and/or severe motions of the unconstrained torso. Pelvic injuries were also attributed to restraint offered by the lap belt on the accelerating torso-pelvis complex in the absence of the armrest. Lower extremity injuries occurred due to the unconstrained motion (flailing mechanism). These results serve as an initial dataset to understand the kinematics of different body regions, injuries and patterns, and potential injury mechanisms describing PMHS responses in the aviation environment.

Injuries to Post Mortem Human Surrogates in Oblique Aircraft Seat Environment.

Increased interest in the airline industry to enhance occupant comfort and maximize seating density has prompted the design and installation of obliquely mounted seats in aircraft. The potential for injury and their mechanism in this seating environment is unknown. Epidemiology-based field injury data do not exist for airplane crashes, however, typical impact scenarios have been determined and safety standards addressing fore, aft, and side-facing seats have been levied by the FAA. The impact scenarios defined in these standards can be used to study likely injuries and injury mechanisms using Post Mortem Human Surrogates (PMHS) in a controlled laboratory environment. Four PMHS were seated upright with Frankfurt plane horizontal in a custom designed seat configured to simulate potential aircraft environments and candidate restraint geometries. A scaled Part 25.562 Emergency Landing condition for horizontal impact was used as the dynamic test input. High speed video recorded occupant kinematics. Pre and posttest x-rays and CT’s were obtained and autopsies were conducted. Severe injuries to the cervical, thoracic, and lumbar spine were observed in three of the four specimens and attributed to torso flail. Pelvis injuries likely caused by the seat belt were found in two tests. Multiple rib fractures were also seen, caused by contact with arm rest or other body regions. The fourth test was run at a lower severity and did not produce injury. This suggests a conservative threshold for human tolerance to this loading environment. Although the study is of a limited sample size, it suggests the need for further testing to develop standards that provide similar levels of safety for obliquely mounted seats as forward/aft facing seats in aircraft.

Investigation of the THOR Anthropomorphic Test Device for Predicting Occupant Injuries during Spacecraft Launch Aborts and Landing.

The objective of this study was to investigate new methods for predicting injury from expected spaceflight dynamic loads by leveraging a broader range of available information in injury biomechanics. Although all spacecraft designs were considered, the primary focus was the National Aeronautics and Space Administration Orion capsule, as the authors have the most knowledge and experience related to this design. The team defined a list of critical injuries and selected the THOR anthropomorphic test device as the basis for new standards and requirements. In addition, the team down-selected the list of available injury metrics to the following: head injury criteria 15, kinematic brain rotational injury criteria, neck axial tension and compression force, maximum chest deflection, lateral shoulder force and displacement, acetabular lateral force, thoracic spine axial compression force, ankle moments, and average distal forearm speed limits. The team felt that these metrics capture all of the injuries that might be expected by a seated crewmember during vehicle aborts and landings. Using previously determined injury risk levels for nominal and off-nominal landings, appropriate injury assessment reference values (IARVs) were defined for each metric. Musculoskeletal deconditioning due to exposure to reduced gravity over time can affect injury risk during landing; therefore a deconditioning factor was applied to all IARVs. Although there are appropriate injury data for each anatomical region of interest, additional research is needed for several metrics to improve the confidence score.

Evaluation of pregnant female injury risk during everyday activities.

Exercise is encouraged for the pregnant female, but there are no data available indicating the risk of fetal loss associated with the level of exercise. The purpose of this study was to assess the risk of fetal loss by simulating exercises using the pregnant computational model. A previously validated MADYMO computer model of a 30-week pregnant female has proven a useful tool in calculating the risk of adverse fetal outcome. Four small female nonpregnant volunteers performed six activities including sitting in a chair normally, walking at 1.3 m/s, running at 2.7 m/s, performing jumping jacks, achieving maximum vertical leap in place, and jumping off of a step 20 cm high. The results for this study are 12 simulations with an average risk of fetal loss equal to 10.0 +/- 4.1%. The minimum risk from the simulations is 3.1% for walking and the maximum risk is 18.8% for running. The low impact exercises have effectively no risk when taken in context with the validation of the computational model from motor vehicle crash data. However, the pregnant female can have an appreciable risk of adverse fetal outcome for the higher impact activities. In conclusion, this study confirms a low risk of adverse fetal outcome for a healthy pregnant female during low impact exercise events.

Pregnant occupant injury risk in severe frontal crashes using computer simulations.

Automobile crashes are the largest cause of death for pregnant females and the leading cause of traumatic fetal injury mortality in the United States. A previously validated MADYMO computer model of a 30-week pregnant occupant was used in this study to investigate the pregnant occupant response in a severe frontal motor vehicle crash. This study presents simulations of 26 different severe car crash tests, encompassing nine vehicle models that represent the compact, medium, and sport utility vehicle classes during the years 1996 to 2006. With the pregnant occupant in the passenger seat, these tests involve a vehicle with an initial velocity of 35 mph into a fixed barrier with the full width of the front of the vehicle. Uterine strain from the computational model indicates the risk of adverse fetal outcome for a pregnant occupant in each vehicle. The average risk of fetal loss associated with these frontal crashes is 85 +/- 13% with a minimum risk of 55% and a maximum risk of 100%. This high risk of fetal loss is consistent with published pregnant occupant case studies that have an equivalent change in velocity. When compared to testing for the average male, this study suggests that current safety standards do not accurately address the risk to a pregnant occupant in a severe frontal crash.

Analysis of pregnant occupant crash exposure and the potential effectiveness of four-point seatbelts in far side crashes.

The purpose of this paper is to present the crash exposure patterns of pregnant occupants and to evaluate the effectiveness of restraint systems, including four-point seatbelts, in far side crashes. The NASS CDS database revealed that 53.0 % of pregnant occupants are exposed to frontal crashes while 13.5 % are exposed to far side impacts. Given that far side crashes were the second leading crash mode after frontal impacts, a previously validated MADYMO computer model of a 30 week pregnant occupant was utilized to investigate pregnant occupant biomechanics in far side crashes. Three impact speeds (5, 15, and 25 mph) were simulated with four restraint conditions: unbelted, lap-belt only, three-point belt, and a four-point belt. Direct abdominal contact from the shoulder strap of the three-point or four-point belt caused uterine-placental strain in contrast to the inertial loading induced strain in the lap-belt and unbelted cases. Overall, the three-point and four-point belt systems provide superior restraint effectiveness for the pregnant occupant compared to the lap-belt and no restraint cases. The four-point resulted in slightly better performance than the three-point belt by reducing the fetal injury risk and occupant excursion.

Biomechanical modeling of pregnant occupants in far-side vehicle crashes.

Automobile crashes are the largest single cause of death for pregnant women and the leading cause of traumatic fetal injury mortality in the United States. The purpose of this paper is to evaluate the risk of fetal injury in pregnant occupants exposed to far-side vehicle crashes. A test matrix of nine computer simulations was performed using a computational model of a 30-week pregnant occupant. Three separate far-side impact severities were modeled including velocity changes of 5 mph, 15 mph, and 25 mph over the same 100 ms period. Three restraint conditions were modeled including no restraint, lap-belt only, and the three-point belt. All simulations at 5 mph resulted in very low risk of maternal or fetal injury. The simulations at 15 mph and 25 mph demonstrated the protective benefit of the three-point belt as both the lap-belt and no restraint tests resulted in the mother's head contacting the opposite door resulting in severe head injuries with HIC values above 2000. All simulations at 15 mph and 25 mph indicate possible fetal injury risk regardless of restraint condition as the peak strain values at the utero-placental interface were between 27.1% and 44.9% which equate to fetal injury risks between 36.9% and 61.0%. Direct abdominal contact from the shoulder strap of the three-point belt caused this strain in contrast to the inertial loading induced strain in the lap-belt and unbelted cases. Overall, the console was not a potential fetal injury mechanism in these simulations as the occupant either passed over it in the unrestrained simulations or rotated above it for the lap-belt and three-point belt tests. The results of this study are consistent with previous studies that show the three-point belt is the best and most important safety device for protecting pregnant occupants.

Evaluating pregnant occupant restraints: the effect of local uterine compression on the risk of fetal injury.

In order to develop effective restraint systems for the pregnant occupant, injury criteria for determining fetal injury risk must be developed. This study presents computer simulations of a 30 week pregnant occupant that illustrate the importance of local uterine compression on the risk of fetal injury. Frontal impact simulations with a range of velocities and belt positions were used to identify the best correlation between local uterine compression and peak strain measured at the uterine-placental interface. It is suggested that future pregnant dummy development and specifically pregnant injury criteria should be based on local uterine compression relative to the placental attachment location.

Computational model of the pregnant occupant: predicting the risk of injury in automobile crashes.

OBJECTIVE: The goal of this study was to create a computational model of the pregnant occupant of a motor vehicle to predict fetal outcome in crashes. STUDY DESIGN: A finite element uterine model of a 7-month pregnant woman was created and integrated into a multibody human model. Unrestrained, three-point belt, and three-point belt plus airbag tests were simulated at speeds that ranged from 13 to 55 km per hour. RESULTS: Peak uterine strain, as determined by the model, correlated well with the risk of fetal death, as determined by investigations of car crashes. The strain in the uterine wall exceeded the limits of the tissue in simulations of no restraint at 35 km per hour and three-point belt tests at 45 and 55 km per hour. The safest restraint for the pregnant driver is the combination three-point belt and airbag. CONCLUSION: The model is a good first step toward the prediction of the risk of fetal death and verified experimental findings that note the importance of proper restraint use for the pregnant occupant.