Abdominal Injury Analysis

The abdominal injuries described in the coroner’s report and summarised in Table 5.1 are consistent with an AIS 1 injury (AAAM, 1990). Exact quantitative data on the mechanisms of abdominal trauma is limited. As noted in the US Department of Transport Collision Avoidance and Accident Survivability Volume 3: Accident Survivability guide produced by Calspan Corporation (1993):

“A large body of clinical literature has evolved over the years that documents the various forms of injuries produced by blunt abdominal trauma. In contrast, there are very little quantitative data available on the loading conditions, force levels and impact velocities that characterize typical accident situations. To date, animal testing has been the prime method for evaluating abdominal injury tolerance.”

As noted in previous sections a range of mechanisms can be related to injury risk including acceleration, compression, power and force with these mechanisms often being rate-dependant. Quantitative abdominal acceleration tolerance would not appear to be readily available, however, the thoracic acceleration tolerance is taken to be 60 G’s for a period not exceeding 3 ms, which is the limit for frontal thoracic acceleration stipulated in FMVSS 208 (1997), and is the loading applied to the entire thorax, including both skeletal and soft tissues.

Alternatively, abdominal injury tolerance to frontal loading can be determined from the force applied to the abdomen. Considerable research has been conducted on the risk of abdominal injury posed by airbag deployment, steering wheel contact and seatbelt loading to vehicle drivers. Hardy et al (2001) conducted a series of tests to determine abdominal injury tolerance to frontal impact by subjecting cadavers to blows from seatbelt impactors, rigid bar impactors and airbag deployment. Johanssen and Schindler (2007) coded the resulting injuries from Hardy et al’s tests and, neglecting the seatbelt injuries (which invariably were in conjunction with thoracic injuries, indicating a lessening of the load applied to the abdomen), produced a chart of risk of AIS 3 or greater injury versus frontal abdominal loading, as reproduced in Figure 5.11.

Abdominal Injury Risk versus Frontal Loading

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

0 1 2 3 4 5 6 7 8

Load (kN)

AIS3 or greater injury risk

As can be seen, a loading of 4 kN indicates a 50% risk of an AIS 3 or greater injury, whilst a loading of 5 kN indicates a 90% risk of such an injury. A loading of 3 kN or less indicates a low (less than 10%) risk of serious injury.

Assuming that pedestrian injury tolerance is equivalent to that derived from testing designed to evaluate the risk of abdominal injury to vehicle occupants a simulation matrix was constructed to evaluate the influence of impact speed and vehicle acceleration for a vehicle-pedestrian collision involving a SUV-type vehicle and provide an additional correlation to the vehicle speed estimates derived from other pedestrian injuries as well as throw distance.

The simulation parameters used to evaluate abdominal injury potential were as described in Table 3.3. An abdominal force sensor was added to the pedestrian model in an attempt to correlate the injury risk to vehicle speed and acceleration. The validation results for a sensor in this location have not been located for this pedestrian model so the results should be treated as comparative only. Furthermore, the value of such a sensor in a multibody model is questionable, although it should be noted that the structure of the human abdomen, consisting mostly of soft tissues, is considerably more homogenous than the thorax (which contains a considerable skeletal component). Taking this into account, it is quite possible that modelling abdominal injuries using a multibody model is more accurate than modelling thoracic injuries using such a model. Having noted this, it should be pointed out that no abdominal injury criteria are included as standard outputs for the MADYMO pedestrian model, but 3 millisecond criteria (continuous and contiguous) and Viscous Injury Criteria (VC) for the thorax are included as standard.

A simulation matrix of five initial vehicle speeds (2, 4, 6, 8 and 10 ms^-1) and five levels of vehicle acceleration (-9, -6, -3, 0 and 3 ms^-2) were analysed and the results are shown in Figures 5.12 to 5.16..

Abdomen Force Resulting from Impact with an SUV-Type Vehicle Decelerating at -9 m/s^2

0 1000 2000 3000 4000 5000 6000

0 500 1000 1500 2000

Time (milliseconds)

Force (N) 2 m/s

4 m/s 6 m/s 8 m/s 10 m/s

Figure 5.12 Abdominal Force Resulting from Impact with Vehicle Decelerating at -9 ms^-2

Abdomen Force Resulting from Impact with an SUV-Type Vehicle Decelerating at -6 m/s^2

0 1000 2000 3000 4000 5000 6000

0 500 1000 1500 2000

Time (milliseconds)

Force (N) 2 m/s

4 m/s 6 m/s 8 m/s 10 m/s

5.13 Abdominal Force Resulting from Impact with Vehicle Decelerating at -6 ms^-2

Abdomen Force Resulting from Impact with an SUV-Type Vehicle Decelerating at -3 m/s^2

0 1000 2000 3000 4000 5000 6000

0 500 1000 1500 2000

Time (milliseconds)

Force (N) 2 m/s

4 m/s 6 m/s 8 m/s 10 m/s

5.14 Abdominal Force Resulting from Impact with Vehicle Decelerating at -3 ms^-2

Abdomen Force Resulting from Impact with an SUV-Type Vehicle Travelling at Constant Speed

0 1000 2000 3000 4000 5000 6000

0 500 1000 1500 2000

Time (milliseconds)

Force (N) 2 m/s

4 m/s 6 m/s 8 m/s 10 m/s

5.15 Abdominal Force Resulting from Impact with Vehicle Travelling at Constant Speed

Abdomen Force Resulting from Impact with an SUV-Type Vehicle Accelerating at 3 m/s^2

0 1000 2000 3000 4000 5000 6000

0 500 1000 1500 2000

Time (milliseconds)

Force (N) 2 m/s

4 m/s 6 m/s 8 m/s 10 m/s

5.16 Abdominal Force Resulting from Impact with Vehicle Accelerating at 3 ms^-2

From the results shown in Figures 5.12 to 5.16 it can be seen that the level of vehicle acceleration/deceleration does not appear to significantly influence the results.

Vehicle impact speed does appear to positively correlate with abdominal injury risk.

A high risk of significant abdominal injury from vehicle contact was only apparent when the vehicle speed was at its highest, namely 10 ms^-1. Abdominal force as a result of a vehicle impact at 10 ms^-1 consistently resulted in over 5 kN of abdominal force whereas impacts with the vehicle travelling at 8 ms^-1 or lower resulted in approximately 3 kN of abdominal force or less. As noted earlier, a loading of 5 kN indicates a 90% risk of an AIS 3 or greater injury whereas a loading of 3 kN or less indicates a low (less than 10%) risk of serious injury. If the abdominal force measurements are valid then the AIS 1 abdominal injury sustained by the pedestrian in the accident case would appear to indicate that the likely vehicle impact speed was less than 8 ms^-1 and quite possibly considerably less.

5.3 Observations Regarding Pedestrian Kinematics Post-Impact and Their