Chevrolet 1994 Astro Passenger Owner's Manual page 39

How The Air Bag
System
Works
Where is the air bag?
The Driver's Facial Air Bag is in the 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 be several 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 and deform
on impact. The air bag is also not 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 on the 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 should have 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.
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