Edwin S. Nowak

Mechanisms of Aortic Injury in Fatalities Occurring in Motor Vehicle Collisions

Case reviews based on autopsy studies have shown that motor vehicle collisions cause between 50 and 90% of traumatic aortic ruptures. Very few studies have analyzed the nature and severity of the collision forces associated with this injury. Our passenger car study (1984-1991) examined 36 collisions in which 39 fatally injured victims sustained aortic trauma. In this injury group, a disproportionate number of heavy truck and roadside fixed-object impacts occurred. Vehicle crash forces were generally severe and were either perpendicular or oblique to the vehicle surface. Intrusion into the occupant compartment was a significant factor in most of these fatal injuries. Occupant contact with vehicle interior surfaces was identified in most cases, and occupant restraints were often ineffective, especially in side collisions. The more elderly victims were seen in the least severe collisions. The most frequent site of aortic rupture was at the isthmus. A majority of victims had rib/sternal fractures indicating significant chest compression. Of the various traumatic aortic injury mechanisms proposed in motor vehicle impacts, the favored theories in the literature combine features of rapid deceleration and chest compression. This study supports that predominant impression, concluding that rapid chest deceleration/compression induces torsional and shearing forces that result in transverse laceration and rupture of the aorta, most commonly in the inherently vulnerable isthmus region.

FATAL INJURIES TO RESTRAINED PASSENGER CAR OCCUPANTS IN CANADA: CRASH MODES AND KINEMATICS OF INJURY

Passenger car collisions with other vehicles and with fixed objects were studied from a representative sample of fatal and injury-producing collisions collected according to a prescribed sampling plan. This paper describes our analysis of accidents involving restrained passenger car occupants who are fatally injured in collisions. Lateral collisions were found to be predominant, and both lateral and frontal collisions were associated with marked intrusion into the occupant compartment, causing direct, severe injuries to the head and chest of these occupants. Multiple severe injuries to more than one body region were common, and 90% of these victims died within one hour of the collision. The seat belt generally offered no protection to these fatally injured occupants. Reducing the incidence of fatal injury to properly restrained passenger car occupants will necessitate diminishing these very severe intrusion forces, especially from heavy trucks and fixed vertical hazards. For vehicle design modifications to be effective, it appears likely that roadway and roadside design and management must be included in the safety equation. Excessive speeds, inadequate traffic control, and unforgiving roadside hazards are playing a major role in the incidence of fatal injuries documented in this study.

EXAMINATION AND ANALYSIS OF SEAT BELT LOADING MARKS

In moderate to severe collisions, large decelerations and hence large forces are generated. Various components of the seat belt system are loaded, and physical evidence of this loading may be observed long after the collision event. Such witness marks result from interaction between different components of the restraint system, or between the restraint and portions of the vehicle interior. Detailed examination and analysis of such marks can establish whether or not the seat belt was in use, and also the precise manner in which the seat belt was worn. Such investigative techniques are critical for evaluating the collision performance of occupant restraint systems, and for positively identifying cases of restraint system misuse. This paper reviews the types of physical evidence which may be observed to determine restraint usage.

A study of injury-producing crashes on median divided highways in southwestern Ontario

The University of Western Ontario Accident Research Team investigates every fatal crash, and approximately one out of every 50 personal-injury crash, within a defined geographic area of three counties. Over a seven-year period, the team investigated 107 collisions (62 fatal and 45 personal injury) that occurred on median-divided highways. These crashes were representative of over 2,300 collisions on the highways involving 81 fatalities and injury to over 3,200 vehicle occupants. Vehicle loss of directional control prior to any impact occurred in 55 of the 62 fatal cases and in 36 of the 45 personal-injury cases. In 36 fatal cases and 17 personal-injury cases loss of control was initiated after a vehicle travelled from the roadway onto the gravel shoulder. Rollover collisions were the most frequent collision type investigated and comprised 25 fatal and 25 personal-injury cases. Unrestrained occupants made up 24 of the 29 rollover fatalities with 96% of these unrestrained occupants being ejected from the vehicle. Collision with an oncoming vehicle after median-crossover occurred in 26 fatal cases. These crashes were usually frontal or side impacts characterized by extensive vehicle damage and massive intrusion into the occupant compartment. Severe head injury (AIS 5 or greater) predominated as the cause of death in all collision types.

Skull fractures in fatalities due to motor vehicle collisions.

A retrospective analysis of 89 fatalities with skull fracture resulting from motor vehicle-pedestrian and various single passenger car frontal, side, rear and rollover collisions was done. Passenger compartment intrusion and occupant ejection were responsible for most, but not all, cranial fractures occurring in impacted motor vehicles. Victims of frontal collisions usually were unrestrained; however, a majority of individuals in cars hit by heavy trucks were wearing seatbelts. Vehicles involved in frontal crashes had crush profiles reflecting a barrier equivalent velocity (BEV) of at least 50 km/h (about 30/mph). In side impacts, most ejected occupants were unrestrained, whereas many of those intruded upon were belted. The minimum BEV calculated in these collisions approached 20 km/h (12 mph). The observation of a skull fracture integrated with accident investigation (that is, determination of head contacts) was useful in the reconstruction of various collisions. Skull fracture patterns, as documented by autopsy, reflected certain kinematic trajectories described in motor vehicle-pedestrian frontal collisions.

Vertical partitions in slender rectangular cavities

Abstract Two-dimensional laminar natural convection heat transfer in slender rectangular cavities equipped with two small vertical partitions, located in the middle of horizontal walls, is studied numerically. The evaluations are carried out for cavity aspect ratios up to 45 and for Grashof numbers, based on the cavity height, up to 5 × 10 8 . As shown, for this range of aspect ratios and Grashof numbers, two small vertical partitions of the same length, made of glass and located in the mid-plane of the cavity, may reduce the cavity mean as well as peak Nusselt numbers by up to 6 and 27 percent, respectively.

The CAV program for numerical evaluation of laminar natural convection heat transfer in vertical rectangular cavities

Abstract To analyze the laminar natural convection heat transfer and fluid flow distribution in vertical rectangular cavities with or without inner partitions, the personal computer finite difference program entitled CAV is used. The CAV program was tested successfully for slender cavities with aspect ratios as high as R = H / L = 90 and for the Grashof numbers, based on the cavity height, up to Gr H = 3 x 10 9 . To make the CAV program useful for a number of applications, various types of boundary conditions can also be imposed on the program calculations. Presented are program applications dealing with the 2-D numerical analysis of natural convection heat transfer in very slender window cavities with and without small inner partitions and recommendations are made for window design.

FURTHER STUDY OF THERMAL CONSTRICTION RESISTANCE AT THE INTERFACE OF DOUBLE‐TUBES

A study of the thermal constriction resistance in a double tube is presented. The general expressions for temperature distribution of the individual tube sector elements are firstly derived. The equations of the thermal constriction resistances may then be obtained. Two special cases, namely the uniform heat flux distribution and the isothermal condition at the land are considered. Under the normal and practical conditions, the case of uniform heat flux distribution at the land may always be employed in the computation of the thermal constriction resistance due to its simplicity.