Thorax Injury Criteria Tolerance Levels

The thorax injury criteria comprise of two different criterions:

• Rib Fracture Criterion (Compression – mm)
• Thorax Internal Organ Injury Criterion (V*C)

Rib Fracture Criterion (Compression)

As shown in Appendix 1, Table 25, in the present chest injury criteria there are several different tolerance levels based on chest compression.  The tolerance levels having to be different for frontal and lateral impacts, due to differences in the chest stiffness relative to its geometry.

In frontal impacts, Kroell (Ref. – 2.1 – Page 376) by analysing a large number of blunt object thoracic impact experiments produced a formula relating chest compression to rib fracture and AIS injury level, which formed the basis of the proposed tolerance levels. A single rib fracture can be sustained without impeding the occupant’s ability of egress and is therefore a Level 1 injury.  As the number increases the injury becomes more debilitating restricting torso and arm movement and therefore requiring assistance to move and is therefore a Level 2 injury.  Over 3 rib fractures there becomes an associated risk of rib cage instability affecting the occupant’s ability to breath, plus the increased probability of the fractured ribs penetrating the internal organs producing a Level 3 injury.  It is unlikely that rib fractures would produce a Level 4 injury except in a blunt object penetrating injury into the thoracic cavity, which is extremely unlikely in a rail interior.

The proposed Rib Fracture Criterion tolerance levels are shown in Appendix 1, Table 26 with equivalent AIS and automotive safety legislation.

In lateral impact no such equation applies.  However taking the tolerance levels from the present injury criteria, Appendix 1, Table 25, and interpolating and extrapolating, the tolerance levels are proposed Appendix 1, Table 27.

As before these have been presented with the present and AIS equivalent automotive legislation Appendix 1 Table 27.

Thorax Internal Organ Injury Criterion

Considerable research work has been conducted on tolerance levels for V*C in thorax injuries and AIS injury tolerance curves have been produced, Lau and Viano, (Ref 2.1 Page 377) for thorax impacts. Then using a probability of an AIS4 injury with the tolerance limits stated in present thorax injury criteria in Appendix 1 Table 25, the Visicus Criteria (V*C ) injury criterion tolerance levels have been proposed.  At present it is proposed to apply these to both frontal and lateral impacts and are used in conjunction with the Rib Fracture Criterion.

AIS injury severity values have been used as it is difficult to specify actual injuries to internal organs in the thorax, due to their different characteristics and locations.  Shown in Appendix 1, Table 28 are the proposed Thorax Internal Organ Injury Criterion tolerance levels with the equivalent AIS and automotive legislation.

Thorax Injury Criteria Summary

Appendix 1, Table 29 summarises all the injury criteria which can be applied to the thorax of the rail occupant.