How Air Bags Work

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Designed to protect the occupants of a vehicle in the case of an accident, air bags inflate when the vehicle collides with another object, or otherwise suffers a sudden deceleration. Absorbing the energy of the impact, vehicle owners need to know the location of the different air bags in their vehicle, as well as any safety concerns associated with air bag use.

Some important considerations include knowing how to deactivate an air bag when necessary, determining when a mechanic needs to replace an air bag, and recognizing common issues and symptoms of air bag problems. Knowing a little about how air bags work can help put it all into perspective.

The Basic Principle of an Air Bag

An air bag system in a vehicle works through the use of sensors monitored by an Airbag Control Unit (ACU). These sensors monitor important criteria like vehicle acceleration, impact prone areas, braking, and wheel speed, among other crucial areas. Upon detecting an impact through the sensors, the ACU determines which air bags to deploy according to severity, impact direction, and a variety of other variables, all within a split second of time. The initiator, a small pyrotechnic device within each individual air bag, generates a small electric charge that ignites the combustible materials that inflate the air bag, helping to lessen the impact damage to an occupant’s body.

But what happens when the vehicle occupant comes into contact with the air bag? At this point, the gas vents through small vent holes, releasing it in a controlled manner. This ensures that the energy from the crash dissipates in a way conductive to preventing injuries. The chemicals most commonly used to inflate air bags include sodium azide in older model vehicles, while newer vehicles usually use nitrogen or argon gas. The whole process of impact and air bag deployment takes place within one twenty fifth of a second. Roughly a second after inflation, the air bag deflates, allowing occupants to exit the vehicle. The entire process happens extremely fast.

Where to Find the Air Bags

The biggest question outside of how an air bag works is where exactly can you find them in your vehicle? Some common areas where vehicle manufacturers place air bags include the front driver and passenger-side air bags, as well as side, knee, and rear curtain air bags, among other locations within the vehicle. Basically, designers try to determine points of possible contact between occupants and the vehicle, such as the dash, center console, and other areas that pose an injury risk from an impact.

Parts of an Air Bag System

  • Air Bag: Made of a thin nylon fabric, the air bag folds into a space in the steering wheel, dashboard, or other location within the vehicle.

  • Crash Sensor: Crash sensors throughout the vehicle help determine the force and direction of an impact. When a particular sensor detects an impact forceful enough, it sends a signal setting off the igniter and inflating the air bag.

  • Igniter: When a strong impact occurs, a small electric charge activates the chemicals around it, creating a gas that inflates the air bag.

  • Chemical: The chemicals in an air bag mix together to create a gas, such as nitrogen, which inflates the air bag. After inflation, tiny vent holes allow the gas to escape, allowing vehicle occupants to exit the vehicle.

Air Bag Safety

Some drivers and vehicle passengers may think that seat belts aren’t necessary if you have an air bag system. But the air bag system itself is not enough to prevent injury in an impact. Seat belts provide a necessary component in a vehicle safety system, especially in a front impact. When the air bag deploys, a pin within the seat belt deploys, locking it in place and keeping vehicle occupants from moving any further forward. Most often, when an air bag deploys, you must also replace the seat belt.

Some of the safety concerns with air bags include sitting too close to the air bag, placing children under the age of 12 in the front passenger seat, and facing infants in the correct direction in the rear of the vehicle according to their age and weight.

When it comes to the distance from the air bag, you want to make sure you sit at least 10 inches away from the air bag in the steering wheel or the passenger-side dashboard. Take the following steps when trying to achieve this minimum safe distance from the air bag:

  • Move the seat back while still allowing room to reach the pedals.

  • Recline the seat back slightly, and also raising it if needed to give you a good view of the roadway while driving.

  • Tilt the steering wheel down away from the head and neck. This way, you direct the impact to your chest area to avoid injury.

Children require a different set of rules altogether. The force of the front passenger-side air bag deployment can injure or even kill a small child sitting too close or thrown forward while braking. Some other considerations include:

  • Using an age appropriate child car seat in the rear seat.

  • Facing infants under 20 pounds and younger than the age of one in a rear facing car seat.

  • If you must place children over one year of age in the front passenger seat, make sure to move the seat all the way back, use a booster or front-facing child safety seat and a properly fitting seat belt.

How to Deactivate an Air Bag

Sometimes, in the case of a child riding in the front passenger seat or a driver with certain medical conditions, you want to deactivate an air bag. This usually comes in the form of an on/off switch allowing you to turn off one or both of the forward deploying air bags in the vehicle.

You might think that in the following cases the air bag should be deactivated, but according to physicians with the National Conference on Medical Indications for Airbag Deactivation, the following medical conditions do not require the deactivation of an air bag, including those with pacemakers, eyeglasses, and pregnant women, as well as an extensive list of other ailments and medical conditions.

Some vehicles include a shutoff switch for the front passenger side-air-bags installed by the manufacturer as an option. Some of the conditions that warrant deactivating the passenger air bag include vehicles with no rear seat, or limited seating that must accommodate a rear facing car seat. Luckily, a mechanic can disable the air bag or install an on/off switch on the vehicle if needed.

Replacing a Deployed Air Bag

Once an air bag deploys, it needs replacing. Air bag sensors located in the damaged section of the vehicle also need replacing after an air bag deployment. Have a mechanic perform both of these tasks for you. Another problem area you might encounter with your vehicle's air bags includes the air bag light coming on. In this case, have a mechanic check out the air bag system to determine the problem and whether or not you need to replace any of the air bags, sensors, or even the ACU.

Another important action item to do to prevent problems with air bags includes having them inspected on a regular basis to determine if they remain safe to use or need replacement.

Common Issues and Symptoms of Air Bag Problems

Be on the lookout for these warning signs that your air bag may have a problem, and then act fast to resolve the problem:

  • The air bag light comes on, signaling a problem with one of the sensors, the ACU, or the air bag itself.

  • After an air bag deploys, a mechanic needs to remove and either reset or replace the ACU.

  • Remember to check the seat belts after an accident to see if a mechanic needs to replace them as well.

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