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Friday, November 09, 2007
Airbag Science 101
The science of airbags is still new and under rapid development. Activities aimed at maintaining and improving the lifesaving benefits of airbags is a high priority. New NHTSA-sponsored tests use improved "dummy" injury criteria based on new knowledge and research.
Until recently, most of the improvements made in auto safety were in front and rear impacts, despite the fact that 40 percent of all serious injuries from accidents are the result of side impacts, and 30 percent of all crashes are side-impact collisions. Many carmakers have responded to these statistics (and the resulting new standards) by making doors, doorframes and floor and roof sections stronger.
But cars that currently offer side airbags are the vanguard of passenger protection. According to engineers, designing effective side airbags is much more difficult than designing front airbags. The bumper, hood and engine absorb much of the impact from a front-impact collision, and it takes almost 30 to 40 milliseconds before it hits the car's occupant. In a side impact, only a comparatively thin door and a few inches separate the occupant from another vehicle. The result is that that door-mounted side airbags must begin deploying in a mere five or six milliseconds!
Engineers at Volvo experimented with different ways of mounting side airbags. The result was they chose to employ seat-back installation because that protects passengers of all sizes regardless of how the seat is positioned. A triggering mechanical sensor is placed on the sides of the seat cushions under the driver and front passenger stops the airbag on the undamaged side of the car from inflating. Installing the entire airbag package in the seat back also offers the advantage of preventing unnecessary deployments that might be caused by collisions with pedestrians or bicycles. A collision of about 12 mph is necessary to trigger side airbags.
Engineers at BMW chose to employ door-mounted airbags. The door, with more space, allows for a bigger bag that provides more coverage.
The head airbag, or Inflatable Tubular Structure (ITS), resembles a big sausage. Unlike other airbags, it is engineered to stay inflated for about five seconds to offer protection against second or third impacts. In conjunction with the side airbag, the ITS is thought to offer superior protection in some side collisions. The curtain airbag is another option for head protection in side impacts.
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