Biomechanics of the Patient Compartment of Ambulance Vehicles under Crash Conditions: Testing Countermeasures to Mitigate Injury

ABSTRACT

There has been very limited research on the biomechanics of occupant safety in the ambulance environment. Occupant protection or crash testing safety standards for these unique vehicles are lacking in the United States. Recent studies have identified ambulances as high risk passenger transport vehicles. This study was conducted to identify some of the occupant safety hazards in the ambulance environment and to determine the efficacy of some countermeasures to mitigate ambulance occupant injury. Accelerator sled testing of the ambulance rear patient compartment (ambulance box or rear cabin) with Anthropomorphic Test Devices was conducted under frontal impact conditions with a target sled pulse was 26 G and 30 mph. The ambulance box was configured with instrumented and uninstrumented Anthropomorphic Test Devices positioned as in the real world environment. Two uninstrumented 95% Hybrid-II Anthropomorphic Test Devices were lap belted and positioned in the occupant compartment, one on the rear-facing attendant’s seat and one on the side-facing bench seat. A Side Impact Dummy was unbelted, seated on the front of the side-facing bench seat and positioned next to a passive restraint device. An instrumented Hybrid-III 3 year old child Anthropomorphic Test Device was restrained in a child restraint system, secured to the gurney via a dual belt path. The actual sled pulse achieved was 34Gs and 34.34 mph, and due to separation of the ambulance box from the chassis/sled, the crash pulse imparted to the patient compartment were 20Gs and 20.9 mph. Head Injury Criterion (HIC) values calculated for the restrained Hybrid-III child Anthropomorphic Test Device were 171, however for the unbelted Side Impact Dummy the HIC was projected to be in excess of 1000. Although this study was a preliminary study, the findings confirmed that there are unique occupant hazards in the ambulance vehicle environment and that certain restraint practices are of value and that some injury mitigating countermeasures are ineffective. Importantly this study also demonstrated the potential for unrestrained occupants to be not only a hazard to themselves but also a hazard to the restrained occupants in the ambulance patient compartment. This study highlights the need for the development of dynamic safety standards for occupant restraint in this environment.