Contrary to popular belief, automobile airbags do not always fire in a collision. However under certain circumstances if they do not and injury occurs, this can be a defect in the automobile.
However, it is important to understand what an airbag can and cannot do. Airbags can be helpful in preventing head injuries and brain damage in both side and head on collisions. They are not very useful in rear end collisions when an individual bounces back and forth. Even so, while sensors are usually placed in the front part of the vehicle, other sensors could be placed in the rear of the vehicle to compensate for the longer periods of passenger reactions in a rear end collision. Inirtial switches can also, and are used by some manufacturers, to also sense unusual collition forces on a vehicle and thus firing the airbags. Thus to determine if the airbag system is defective requires a skilled attorney who has at his disposal engineers knowledgeable in this area.
In some automobiles, the airbag is also designed to work in conjunction with the seatbelt to not only restrain the person in the seat but also prevent movement during the crash sequence. Seatbelts can be designed with what is called a ballistic device that tightens the belt in a collision so that the body does not move around while the crash is taking place. The ballistic device is usually part of the airbag system and operates from the same sensors. Thus, if the airbag does not fire in a collision, the seatbelt also must be examined to see if it did its job or failed.