Our practice > How An Air Bag System Works
When your car, truck, SUV or van is involved in an accident, the airbag sensors are the first components to detect the crash. In earlier vehicles, these sensors were basic switches that responded to changes in velocity as the vehicle slowed down during the crash; once two sensors “closed” to confirm that a crash was taking place, electrical current was allowed to flow to the air bag modules. In newer vehicles, electronic sensors measure the deceleration (negative acceleration) of the vehicle, process it mathematically through a computer algorithm, and then compare the measured values to the values stored inside it from crash testing. If the measured values indicate the crash is more severe than the stored crash tests, the control module would allow electrical current to flow to the air bag modules.
Once the electrical current is flowing to the airbag modules, it heats up a “squib” within the inflator that has a small filament inside a container of chemically explosive or flammable material. Once the filament gets hot enough, the chemicals begin to burn. This burning sets off a larger reaction of a chemical called sodium azide within the inflator, which rapidly produces nitrogen gas, along with numerous byproducts. In some vehicles, the sodium azide inflator was replaced with an inflator using pressurized gas, usually a combination of helium and argon. With either type of inflator, the gas from the inflator then fills the fabric airbag that was folded over the inflator.
As the gas fills the air bag, it increases in size, eventually breaking out from behind its plastic cover, and inflating to its maximum size. Driver airbags are generally shaped like a round pancake just larger than the diameter of the steering wheel, and are normally about 12 to 20 inches thick when filled. Passenger airbags are generally about 2 to 3 feet wide, and fill the space between the passenger and the dash or windshield. Thus, passenger airbags are usually 2 to 4 times larger than driver air bags, and require a more forceful inflator to fill that larger size in the same amount of time.
For frontal airbags, the process of sensing the crash and inflating the air bags is usually over in less than one-tenth (1/10) of a second! As the forces of the crash propel the consumer forward into the air bag, it begins to absorb the energy by compressing, and by letting some of the gas out through the fabric or through specially-designed vent holes. This explains why many consumers who have been involved in an accident during which air bags have deployed remember the distinct chemical odor of the inflation gas and remember seeing smoke in the car.
For side airbags, curtain airbags and rollover airbags, the process is similar. A sensor in the side structure of the car, or sometimes inside the front door, detects the rapid deceleration from the side or the vehicle beginning to rotate upwards during a rollover crash. Electrical current is then sent to the side airbag, curtain airbag or to the rollover airbags (depending on the type of crash), which causes those airbags to deploy; although the chemicals and gases may be different than for front airbags, the inflation process is very similar.
When a side airbag deploys, it breaks out either from the side of the seat nearest the door, or from behind a plastic trim panel on the side of the car. They are much flatter than the frontal airbags, and sometimes smaller: some older side airbags protected only the person’s chest, while others protected both the chest and head. Canopy or rollover airbags deploy from overhead, and are also fairly flat, but extend along the side of the vehicle to protect the head and chest, and to reduce the risk of the consumer being ejected through an open or shattered window. Side curtain airbags can be either designed to deploy only in a side impact crash, or designed to deploy when they sense the vehicle is about to roll over.
What I have described here is the general function of a typical airbag system. As you can see, the air bag system is fairly complex. Therefore, a failure or defect in any one of the components can cause the entire system to malfunction. In some cases, airbags have deployed in very minor crashes (or even when there is no crash), which can lead to devastating results. In other cases, due to improper design and testing, airbags have failed to deploy in head-on frontal collisions. Some of these air bag non deployments have occured even when the closing speed has been over 60 miles per hour.
We offer further information about both of these air bag failures in additional articles by Taras Rudnitsky, an airbag lawyer, former airbag engineer and court-recognized expert witness who accepts cases throughout the United States. If you feel that your airbag system may not have performed properly during an accident, or if the airbag went off for no reason and caused an accident, please do not hesitate to contact me so that I can help you determine why your airbag failed to work properly.