Airbag Inflation-Induced Injury Biomechanics

The basic principles of airbag restraint have been discussed in Chapter 8. The primary advantages of an airbag system over a standard belt restraint system are the potential to distribute the restraining force over a large portion of the body area, including the head, and the potential to provide additional controlled stopping distance within the occupant compartment. Distribution of restraining force eliminates areas of high force concentration and minimizes localized body deformations and reduces relative motions between adjacent body parts. If used effectively, the additional stopping distance will result in the reduction of the forces needed to decelerate the body. Accordingly, the airbag has the potential to enhance the performance of a belt restraint system, particularly when belt force-limiting features are included. When the airbag is used as the only restraint and it cannot rely on the belt system for restraint early in the crash sequence, a more demanding burden is placed on the performance of the airbag system. To provide good restraint, the airbag must be deployed into the space between the occupant and the car interior in a timely manner, prior to the occupant moving too far into that space. In addition the airbag must have sufficient depth and internal pressure to prevent the occupant from fully compressing the bag in severe collisions. The use of a belt restraint in conjunction with an airbag can make both the timing and capacity requirements less critical, but many design dilemmas remain in matching the performance of an airbag restraint system to a particular vehicle design. This chapter addresses some of these dilemmas and the Biomechanics of the special injury consequences that result from the airbag under certain circumstances. These special injury outcomes are known as inflation-induced injuries (IIIs; also abbreviated as I3). Discussions of belt restraint-related injuries can be found in the chapters in this book dealing with thoracic and abdominal trauma.