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High-Tech Vehicle Safety Systems
Advanced 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. Advanced systems feature sophisticated sensors and multi-stage inflators to better tailor the deployment characteristics to the requirements of specific occupants.
How do they work?
The first generation of air bags followed a relatively simple deployment strategy. There was a collision severity, the deployment threshold, below which the air bags did not fire. The seat belt system provided adequate protection in such minor crashes. Above this severity threshold the computer-based control system commanded deployment of the air bags. For belted occupants, the deployment thresholds were rather low, and the air bag deployment characterstics overly aggressive, resulting in air bag induced injuries and even some fatalities. Driver's air bag deployment
The injury risk was a particular concern for certain categories of occupants, namely short statured female drivers and child passengers. Female drivers are typically in closer proximity to the air bag module in the steering wheel than are their male counterparts. Similarly, the heads of infants in rear-facing child restraints in the right front seat are essentially adjacent to the deploying passenger air bag. And, young children occupying the right front seat are at risk of air bag induced injury when grossly out of position, such as by being unrestrained, or using only the lap belt with the shoulder belt placed behind their back, such that their head and chest move forward in a crash.
Second generation air bag systems were introduced into vehicles in the 1998 model year. These systems were termed "depowered" because the main design change was to reduce the amount of propellant in the pyrotechnic gas generator in order to provide a softer deployment. Additional changes to the system included recessing driver air bag modules into the steering wheel, modifying bag fold patterns, and using additional tether straps on the fabric to control the bag shape as it deployed.
Further enhancements to the technolocies resulted in the development of advanced air bag systems, sometimes termed "smart air bags". Typically, advanced air bags use a dual inflation system with the capability to produce either a low-level or high-level deployment. The high-level deployment is approximately the same as that of a depowered or second-generation system. In addition, specific sensors are employed to characterize the nature of the occupant, and command an appropriate deployment.
A sensor on the track of the driver's seat determines whether the seat is adjusted forward or rearward. If the seat is forward on the track, the occupant will be closer to the air bag module, and the control system inhibits the high-level deployment. The deployment algorithm also uses other parameters, such as crash severity and seat belt use, to determine the level of deployment. So, for example, a first-stage deployment may occur for a belted male driver, with the seat fully rearward, if the crash severity is so low that a full air bag deployment is deemed to be unwarranted. Alternatively, if the crash is of high severity both stages of air bag inflation may be initiated to produce a high-level deployment.
In the right-front passenger seat most systems use a weight sensor to determine if the seat is unoccupied in which case deployment of the passenger air bag will be inhibited. The weight sensor can also discriminate between children and adults who may be occupying the seat. Typically, air bag deployment will be suppressed if the sensor identifies a low-weight condition. In such cases, a warning light on the dashboard alerts the occupant to the situation. Other technologies used to modify the air bag deployment characteristics include optical, infrared, ultrasonic and electric field sensors to determine occupant proximity to the air bag module.
Are there any risks?
Even though advanced air bag systems have many new safety features, they are still pyrotechnic devices and, consequently, their deployment is extremely rapid. It is important, therefore, that vehicle occupants should not be too close to air bag modules.
All occupants should use the available seat belt systems to prevent any unnecessary forward motion. Drivers should adjust their seat as far rearward as is practicable while maintaining access to the vehicle's controls. Passengers too should adjust their seats as far back as possible.
Even though air bags should be automatically suppressed in the presence of a child restraint system, especially rear-facing infant carriers, child passengers 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).
What can science tell us?
Second Generation Air Bag Systems: A Preliminary Evaluation of Field Accident Experience; Dainius J. Dalmotas, Alan German and Regina M. Hurley; Proc. CMRSC-XI; Halifax, Nova Scotia; May 9-12, 1999
This paper presents preliminary results of a study of real-world crashes involving second generation air bags. Despite the relatively small dataset, there is some anecdotal evidence that the combination of seat belt systems and second generation air bags provide good occupant protection in moderate to severe crashes. This outcome is consistent with the dummy responses measured in vehicle crash tests.
Initial Evaluation of Advanced Air Bags in Real World Crashes; John Brophy, Michael S. Parsons and Augustus "Chip" B. Chidester; Paper No. 05-0386; Proc. 19th ESV Conf.; Washington DC; June 6-9, 2005
Preliminary data from real-world collisions investigated as part of NHTSA's Special Crash Investigation (SCI) programme show only minor to moderate levels of injury for occupants involved in frontal crashes in which advanced air bag systems deployed.
- 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