Extremity Injury Criteria Tolerance Levels

The Extremity injury criteria comprise of five different criterions.

• Long Bone Injury Criteria (Fracture Index)
• Knee Dislocation Injury Criterion (mm)
• Shoulder Impact Criterion (ms-1)
• Hand Fracture Criterion (ms-1)
• Hand Laceration Criterion (ms-1)

Long Bone Injury Criteria

Fracture Index

Each long bone has an individual fracture index based on its own ultimate bending moment and axial compressive strength, using the equation below.

Fracture Index (TI) =   Actual Bending Moment    +    Actual Axial Compressive Force

                                  Ultimate Bending Moment      Ultimate Axial Compressive Force

The full list of Fracture Index Criteria is given below with the ultimate bending moments and axial compressive force are presented in Appendix 1, Table 38.

• Humerus Index Criterion
• Ulna Index Criterion
• Radius Index Criterion
• Femur Index Criterion
• Tibia Index Criterion

·         Fibula Index Criterion

The fracture index predicts a single fracture (non-comminuted) at a value of 1 with a complex (comminuted) at a value of 1.3.  Applying these to the proposed injury classification system, will depend on where the fracture is located.

Any fracture to the leg will obviously greatly affect the occupant’s ability to egress the rail vehicle, requiring another occupants assistance; therefore a fracture index of 1 to the femur, tibia or fibula will have an injury Level 2.  Although not life threatening, comminuted and exposed fractures will require medical assistance so therefore a fracture index 1.3 will have an injury Level of 3.

Fractures to the arms are less serious, an occupant being able to egress the rail vehicle with a simple fracture, so a fracture index of 1 to the humerus, radius and ulna, would have an injury Level of 1, while a fracture index of 1.3 an injury Level of 2.

Appendix 1, Table 39 shows the proposed Fracture Injury Criterion tolerance levels for the legs followed by the arms, in Appendix 1, Table 40, with the equivalent automotive legislation and AIS.

Knee Dislocation Injury Criterion

Displacement (mm)

The knee dislocation injury criterion predicts the severity of knee dislocation and cruciate ligament rupture, by measuring the longitudinal shear displacement between the tibia and femur.  Knee dislocation is never life threatening, however it can affect the occupant’s ability to egress a rail vehicle and also lead to long term disabilities.  Therefore a dislocation of 15 mm has been proposed as a Level 1 injury, which is unlikely to rupture the cruciate ligament, producing cartilage and soft tissue damage, but not seriously affecting the occupants motion.  Rupturing of the cruciate ligament with total dislocation of the knee would require assistance from another occupant, with potential long term disabilities.

Appendix 1, Table 41 shows the proposed Knee Dislocation Injury Criterion tolerance levels, with the equivalent automotive legislation and AIS.

Shoulder Injury Criterion

Impact Velocity (ms-1)

Due to the complexity of forces and the large number of different impact scenarios, direct impact velocity has been proposed as the injury criterion for predicting shoulder injury.  As shoulder dislocation and injury is never life threatening, an injury Level 3 and 4 are not applicable.  Low velocities <2ms-2, would only produce minor contusions.  However, as the impact velocity rises, fractures to clavicle or dislocation of the shoulder occurs, which would severely impede an occupants ability for egress, producing a Level 1 injury.  A tolerance level of >5 ms-1 is proposed for a Level 2 injury.

Appendix 1, Table 42 shows the proposed Shoulder Injury Criterion tolerance levels for which there is no equivalent safety legislation only AIS.

Hand Fracture Criterion

Impact Velocity (ms-1)

The Hand Fracture Criterion was proposed to predict the probability of sustaining a hand fracture from impact with a rigid blunt object.  Despite not being life threatening it could impede an occupant’s ability of egress, if compounded by a number of this level of injury, causing long-term disability.  This would therefore produce a Level 1 injury for which an impact velocity of 5ms-1 has been proposed.

Hand Laceration Injury Criterion

Impact Velocity (ms-1) / Impact Object Shape (Sharp / Blunt)

Lacerations to the hand and arm are not life threatening but occur frequently in impacts with both blunt and sharp objects.  If severe these can directly affect the operation of the hand and arm by cutting ligaments and tendons, therefore reduce the occupant’s ability of egress, producing Level 2 injuries.  The impact velocity for producing such injuries would be lower for a sharp, <5 mm radius, object than a blunt, 5 – 40 mm radius.  Therefore an impact velocity of 8 ms-1 has been proposed for a blunt object and 5 ms-1 for a sharp.  A Level 1 injury being proposed as 5 ms-1 and 2.5 ms-1 respectively.

Extremity Injury Criteria Summary

Appendix 1, Table 43 summarises all the injury criteria, which can be applied to the extremities, arms and legs of the rail occupant.