3.1       Summary

Occupant injuries in rail accidents are caused by the occupant impacting interior features, such as seats, tables, walls and grab handles.  The severity of the impact being dependent on the velocity of the impact and the shape and dynamic stiffness of the impacted feature. The resulting injury and its severity will depend on what part of the occupants body actually impacts.  In the ‘Injury Mechanisms and Injury Criteria’ all the major constituent parts of the body are reviewed in terms of five main items.

• Definition and main anatomy of that body part

• The main types of impacts and loading that each body part could sustain

• The main injuries and injury mechanisms that result for those impacts

• The injury criteria, which best predicts the severity of the injury for each injury type and mechanism

• Injury criteria tolerance levels to the five levels in the injury Severity Classification System

Injuries can be produced by two main mechanisms.  Firstly by direct impact, where the rapid acceleration of that particular body part’s mass produces the inertia loads resulting in a direct injury.  Secondly, by indirect loading, where the loads are generated not by the inertia of that body part, but, by the acceleration forces of the whole body transferring loads through that body part.  Injuries to the neck and pelvis are usually caused by this mechanism.

The human body has been divided into six main areas dependent on the type of impact, function and engineering properties.

Head including face – an exposed body part having frequent impacts and contains the life supporting brain.

Neck – Rarely sustaining a direct impact but can have life threatening indirect load injuries.

Thorax – Contains the vital life supporting organs of lungs, heart, liver, and spleen, which can be injured from a direct impact.

Abdomen – Although can sustain direct impacts from table edges and armrests it rarely has life threatening injuries.

Pelvis – Rarely has direct impacts however indirect loads can produce pelvis fracture, which although not life threatening can seriously affect the occupants ability of egress.

Extremities – Injuries to the arms and legs are not life threatening, but are the most exposed and frequent body part sustaining impacts. Injuries can seriously affect the occupants ability of egress.

Then for each body part the main injury mechanisms are reviewed for which injury criteria are proposed.  These are based on the biomechanical dynamic characteristics of that body part and the injury mechanism.  When these injury criteria can be applied and how they are used is also proposed along with the present physical and computer techniques for evaluating them.

Tolerance levels for the five Injury Severity Levels have been proposed which are used in occupant protection evaluation technique.