High-Tech Vehicle Safety Systems

Front Air Bags

Front air bags, for the driver and right-front passenger, mainly provide protection against head contact with the steering wheel and dashboard. They are designed as supplementary restraint systems (SRS), meaning that the protection they provide is in addition to that offered by the use of a regular lap-and-shoulder seat belt.

How do they work?

Driver's air bag deployment

Image courtesy of Technology Associates

Air bags are computer controlled. Sensors monitor the vehicle's deceleration and determine when a collision is occurring. If the crash is of sufficient severity, the computer commands the air bags to deploy. All this happens very quickly - typically in just a few hundredths of a second - faster than the blink of an eye! The air bag firing circuit is activated, the chemical propellent ignited, and the gas generated inflates the fabric of the air bag. This creates a cushion, spreading the forces of collision and allowing the occupant to avoid any hard contacts with portions of the vehicle's interior.The first generation of air bags followed this relatively simple deployment strategy. There is a collision severity, the deployment threshold, below which the air bags will not fire. The seat belt system provides adequate protection in such minor crashes. The vehicle's computer uses multiple criteria to judge if air bag deployment is required, thus it is not possible to give a single collision speed below which the air bags will not fire.

Air bag componentsThe chemical propellent is burnt and produces nitrogen gas, an inert component of normal air. Vehicle occupants often see "smoke" and believe that their vehicle is on fire. However, this is mostly a cloud of talcum powder coming from the folds of the air bag fabric where it is used as a lubricant to allow the bag to unfold smoothly.

Where a vehicle is equipped with dual (driver and right-front passenger) first-generation air bags, both air bags will normally be fired at the same time. But, some early-model vehicles were equipped with only a driver's air bag. Crash sensors respond to primarily frontal impacts. Consequently, air bags may very well not be deployed in rear-end collisions, side impacts, and rollovers. In angled frontal crashes deployment of the air bag is dependent on both the crash severity and the direction of the collision force (i.e. an impact more from the side than from the front may not deploy the bag.)

Are there any risks?

Because air bag deployment happens so rapidly, it is extremely important that vehicle occupants should not be too close to the air bag modules. These are generally located in the steering wheel hub and the upper right-front dashboard. There would be significant risk of head, neck and chest injury if an occupant were to be struck by the flaps of the air bag cover as they open (punch out), or by the rapidly expanding fabric of the bag as it is inflated (membrane loading). Most agencies recommend that occupants should be at least 25 cm (10 inches) away from the air bag module. Children are at special risk (see next section).

Children and air bags

Child passengers in the right-front seat of vehicles equipped with air bags are of particular concern. Rear-facing infant carriers should never be installed in the right-front seat when there is an air bag. This would place the child's head much too close to the passenger's air bag module. Many children have been killed or seriously injured in this manner. Similarly, most agencies recommend that children aged 12 and under should be seated in the rear of the vehicle with an age-appropriate restraint system (infant carrier, child seat, booster cushion and seat belt). Children frequently don't sit still in vehicles. They will often sit on the edge of their seat, lean forward, and may even slip their body out of the seat belt or child restraint harness. If a child were to do this in the right-front passenger's seat at the very instant that a collision occurred, they would be out of position and too close to the air bag, and this could easily result in serious injury or fatality.

What can science tell us?

  • Air bag deployment Airbags Technology.pdf (544 downloads) ; German A, Dalmotas DJ, McClafferty KJ, and Nowak ES; Advances in Transportation Systems, Proc. CSME Forum 1996; Hamilton ON; 1996This paper includes an overview of first-generation air bag technology, real-world collision experience with these systems including unusual injury mechanisms, and an outlook on future developments (2.1 MB PDF, 8 pages, 33 references)
  • Airbags Canadian Fatalities.pdf (496 downloads) ; German A, Dalmotas D, Tylko S, Comeau J-L and Monk B; Proc. CMRSC-XIII; Banff, Alberta; June 8-11, 2003This paper reviews a series of low severity crashes involving air bag induced fatalities that have been researched in detail. The resulting implications for the design and testing of future safety systems, their regulation, and the dissemination of relevant information to vehicle users are discussed. (594 KB PDF, 18 pages, 15 references)

Useful links

Quick Facts

  • Always wear your seat belt; air bags only provide additional protection!
  • Sit as far back from the air bag as you can. Let the bag inflate and do its job!
  • Never install an infant carrier in the right-front seat
  • Children aged 12 and under should be in the rear seat away from air bags
  • Check the owner's manual for specific information about the air bags and seat belts in your vehicle

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