Objectives
The objective was to identify hazards and risks in ambulance transport, by combining epidemiological and biomechanical approaches to hazard and crashworthiness data collection and analysis. The epidemiological approaches include mining federal databases and field data collection. The biomechanical approaches include conducting crash tests of ambulance vehicles under real world crash circumstances to determine what forces occur on the vehicle and the occupants and to test injury mitigating countermeasures for occupants.
Methods
Epidemiological data and field data were collected to identify the configurations of the interior of the ambulance environment and occupant distribution. The epidemiological data included an 11-year retrospective analysis of emergency vehicle crashes. The field data included an observational survey of 200 ambulances arriving at an urban emergency department in addition to survey of EMS providers for their exposure to injury and injury mechanisms. Standard ambulance vehicles were configured with anthropomorphic test devices (ATDs) and medical equipment, based on these prior studies. Based on the epidemiological data, full vehicle to vehicle crash testing was conducted of intersection crash scenarios, each involving two vehicles. The vehicles were selected to represent late model Type I, Type II and Type III ambulance vehicles. Instrumented ATDs, including a 3 year-old child, adult male and adult female and medical equipment, were positioned in the rear patient compartment in variable restraint configurations and seating positions to model the real world environment. Existing currently available seat belts and standard child safety seat were the only injury mitigating devices tested in this environment. The vehicles and gurney were instrumented with accelerometers. The vehicles were tested in both head-on and side impact scenarios for the 34 mph frontal and the 44 mph side impact crash tests, respectively. Data captured from the accelerometers, high speed digital video and colored impact residue material was analyzed by the multidisciplinary team. In test 1 the Type II vehicle struck the Type I vehicle on its right hand forward side. In test II the Type III vehicle struck the Type II vehicle on the center of its left side.
Data Sources
The emergency vehicle crash data were obtained from FARS 1989–2000, GES 1989–99, and NTSB 1979, and the Calspan Veridian crash test site. Electronic data were captured from the instrumented ATDs in addition to the instrumentation of the test vehicles accelerometers positioned on the vehicle floor and gurney, digital video, with high-speed 1000 frames/sec film, and colored impact residue material.
Results
Epidemiological data suggest that intersection crashes are associated with high morbidity and mortality, particularly to unrestrained rear occupants. Field data identify numerous diverse seating positions for providers, family members, and patients; there is frequent lack of use or inadequate use of available occupant systems. In the crash testing, occupant kinematics and forces demonstrated effective techniques for securing the child patient occupant. Testing clearly demonstrated that unsecured occupants are a risk to both themselves and also to other occupants. Anticipated potential injury mechanisms were clearly demonstrated with head impacts for unbelted occupants onto hostile interior surfaces. Data collected from the vehicle positioned accelerometers suggest a crash pulse that differs from the standard FMVSS 203 passenger vehicle crash test pulse.
Conclusion
Ambulance transport is associated with predictable and likely preventable occupant hazards. Intersection crashes have high injury and fatality risk. Crash testing demonstrates that the ambulance transport environment includes predictable and preventable occupant risks. Failure to use current methods of occupant protection for each occupant or to secure equipment effectively can result in catastrophic outcomes to all occupants. Hostile interior surfaces suggest a need to modify the ambulance interior, including optimization of the restraint systems and improved head protection for the occupants. There is an urgent need for dissemination of this safety information and to develop data driven performance based safety standards and designs in the USA.
Discussion
This study is one of few studies that address the issue of emergency vehicle safety from a combined epidemiological and engineering perspective. It also provides the first set of crash test pulses generated for real world ambulance vehicle crash circumstances. Development of an industry based task force to further address the safety of ambulance transport and predictable and preventable occupant risks in the ambulance transport environment should be embarked upon. There are a number of developments in recent years internationally on the safety of ambulance transport. Identification and integration of these innovations and concepts could enhance the safety of USA EMS. EMS vehicle crash injury reporting systems would enhance safety evaluation for an EMS safety intervention.
Limitations of Study
Without true and detailed denominator data on total number of ambulance vehicles, total number of miles traveled, and restraint usage occupant numbers and types, with and without lights and sirens use, it is challenging to ascertain true relative risks of certain practices. This study provides a glimpse at potential strategies to optimize the safety of ambulance transport. There were a number of approximations in place in this study from a testing perspective, which may have resulted in an underestimate of the degree of hazard. Restraint practices used in this study reflected a more optimal situation than real world scenarios. There was only one unrestrained occupant and no unrestrained equipment. This was due to the extreme expense of the possible damage to the ATDs should there have been more than one unrestrained occupant, or unrestrained medical equipment. Also due to the logistics of modeling a full vehicle intersection crash for such large vehicles, only one vehicle was in motion at the time of the crash. Additionally ATDs are not designed for rear facing or recumbent orientations. However, there are not yet specifically designed ATD for this type of environment.