1994 Chevrolet Astro Owner's Manual - Page 39

How The Air Bag System Works Where is the air bag? The Driver's Facial Air Bag is inthe middle of the steering wheel. When is an air bag expected to inflate? The air bag is designed to inflate in moderate to severe frontal or near-frontal crashes. The air bag will only inflate if the velocity of the impact is above the designed threshold level. When impacting straight into a wall that does not move or deform, the threshold level is between 11 and 16 mph (17 and 23 km/h). However, this velocity threshold depends on the option content of the vehicle and may beseveral miles-per-hour faster or slower. In addition, this threshold velocity will be considerably higher if the vehicle strikes an object such as a parked car which will move anddeform on impact. The air bag is alsonot designed to inflate in rollovers, side impacts, or rear impacts where the inflation would provide no occupant protection benefit. In any particular crash, the determination of whether the air bag should have inflated cannot be based solely onthe level of damage on the vehicle(s). Inflation is determined by the angle of the impact and the vehicle's deceleration, of which vehicle damage is only one indication. Repair cost is not a good indicator of whether an air bag shouldhave deployed. What makes an air bag inflate? In a frontal impact of sufficient severity, the air bag sensing system detects that the vehicle is suddenly stopping as a result of a crash. The sensing system triggers a chemical reaction of the sodium azide sealed in the inflator. The reaction produces nitrogen gas, which inflates the cloth bag. The inflator, cloth bag, and related hardware are all part of the air bag inflator module packed inside the steering wheel. 1-27