Automobiles are equipped with safety devices commonly referred to as "Air Bags." Air Bags are designed to protect passengers from direct impact with hard interior vehicle parts in the event the vehicle is involved in a collision. If the vehicle is involved in a collision, a triggering system activates a device which rapidly inflates the air bag. The inflated air bag provides a cushion for the passenger to impact, reducing the chance of injury, or reducing the severity of injuries resulting from the collision.
Current air bag inflation devices operate quickly enough to meet current industry requirements. The need exists, however, for faster acting air bag inflation devices which will satisfy new industry requirements for dealing with higher speed front collisions and for certain side impact collisions.
Passengers sitting near vehicle doors are much closer to the point of collision during a side impact than they are to the dashboard or steering wheel during a front end collision. Conventional air bag inflation devices act too slowly, when inflating air bags in side doors, to protect passengers from severe side impacts.
Gas used to inflate air bags mush not be toxic or cause burn injuries to passengers, and it must not present environmental hazards in use or during disposal.
Currently, industry employs two types of air bag inflation devices. One type uses sodium azide blended with a suitable oxidant such as molybdenum-disulfide or potassium nitrite to control burn characteristics. Upon ignition, these devices produce predominantly nitrogen gas which evolves from thermal decomposition of the sodium azide. Unfortunately, sodium azide is both explosive and a very toxic poison. This creates a major risk to passengers, and presents serious disposal problems.
The second type of device, referred to as a hybrid, involves the storage of an inert gas (e.g. argon) under pressure along with a pyrotechnic or propellant. This propellant serves two functions. First, at ignition the propellant produces heat and gas which pressurizes the argon gas so that the argon ruptures a rupture disc (or activates another suitable release mechanism) to deliver the argon to the air bag. Second, in some designs, the propellant itself produces gas which adds to the stored argon gas pressure for release into the air bag.
In both the azide and hybrid designs, there is a significant quantity of pyrotechnic material which, when burned, produces substantial particulate reaction products. Great engineering effort is required to filter these particulates from the gas delivery stream in order to meet the industry requirements for maximum allowed quantities of particulates delivered to the air bag. There are also small quantities of toxic gases given off by the burning pyrotechnics. It is very difficult to tailor the pyrotechnic mixture to sufficiently reduce toxic effluents to meet industry standards.
Both the hybrid and azide technologies require major engineering studies to formulate pyrotechnic chemical compositions, particle sizes and distributions, and ignition train mechanisms which satisfactorily control the chemical and pressure-time delivery characteristics of the inflation device. This means that variations in pressure-time delivery requirements between one car model and another require major engineering effort. In most cases, this also requires reconfiguration of the containment vessel and mounting hardware.