October 2004 - Accident Reconstruction Newsletter

About Air Bags

Air bags are supplemental restraints and are designed to work best in combination with safety belts.

• Both frontal and side-impact air bags are designed to deploy in moderate to severe crashes.
• Air bags reduce the chance that an occupant's upper body or head will strike the vehicle's interior during a crash.
• To avoid an air bag-related injury, always ensure proper seating position.
• Read your owner's manual for specific information about the air bags in your vehicle.

Air Bag Module

• The air bag module consists of the air bag and its inflators.
• In a moderate to severe crash, the inflators fill the air bag with harmless gas.
• The driver frontal air bag is located in the hub of the steering wheel.
• The passenger frontal air bag is located in the instrument panel.
• Side-impact air bags can be located in the seat back, the door or the overhead roof rail.

Crash Sensors

• The crash sensors' purpose is to measure how quickly the vehicle slows down in a frontal crash, or is crushed in a side-impact crash, and send those signals to the Electronic Control Unit (ECU).
• Crash sensors for frontal crashes can be located in the front of the vehicle near the engine or in the passenger compartment, sometimes in the ECU.
• Crash sensors for side-impact crashes can be located in the ECU, in the door, in the doorsill or in the pillar between the front and rear doors.
• Severe or panic braking alone cannot cause sufficient force to deploy an air bag.

Electronic Control Unit (ECU)

• The ECU acts like the brain of the air bag system; it receives signals from the various sensors and decides if and when each air bag should deploy.
• The ECU is typically located in the middle of the vehicle, where it is well protected.
• In advanced air bag systems, the ECU can also receive inputs from additional sensors that detect occupant weight, seating position, seat belt use and seat position to determine the force with which the frontal air bags should deploy.

Air Bag ON-OFF Switch

• Most vehicles without rear seats, or with small rear seats, such as pickup trucks or sports cars, have a passenger air bag ON-OFF switch as standard equipment.
• The purpose of the switch in the OFF position is to disable the passenger frontal air bag to transport, for example, a child age 12 or under in the right front seating position.
• Vehicles with enough space in the rear seat to accommodate a child safety seat are not allowed to have an ON-OFF switch as standard equipment.
• Consumers who wish to have an ON-OFF switch installed for either the driver or passenger frontal air bag must apply for an ON-OFF switch.

During an Air Bag Deployment

• When there is a moderate to severe crash, a signal is sent from the Electronic Control Unit (ECU) to the inflator within the air bag module.
• An igniter in the inflator starts a chemical reaction that produces a gas that fully inflates the air bag within the blink of an eye, less than 1/20th of a second.
• The gas is typically nitrogen or argon and is harmless.
• Side-impact air bags inflate even more quickly since there is less space between the occupant and the striking object, such as another vehicle, a tree or a pole.
• Because air bags deploy very rapidly, serious or sometimes fatal injuries can occur if the occupant is too close to, or is in direct contact with, the air bag when it first begins to deploy.
• Nontoxic cornstarch or talcum powder is often used to aid air bag deployment. It is the "smoke" you may have seen released into a vehicle's interior in demonstrations.

After an Air Bag Deployment

• The air bag automatically deflates as the gas escapes through vents in the fabric of the air bag. Air bags cannot smother you and don't restrict your movement after the crash.
• The whole process of air bag inflation and deflation occurs in less than one second.
• The powdery starch or talcum substance used to lubricate the air bag may initially contain small amounts of sodium hydroxide and may cause some temporary minor irritation to the eyes or throat.
• Other minor injuries can include abrasions from contact with the fabric of the air bag.
• Remember: Air bags cannot be reused—they are a single-use safety restraint.
• Do not drive your vehicle until the air bag has been replaced by an authorized repair center.

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