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Old March 17th, 2008, 16:56   #20
spacemoose's Avatar
Join Date: Aug 2006
Originally Posted by BBS View Post
ouch...that was a scary accident. what did you hit to cause the hood to fold up, while the front bumper didn't get crushed? Perhaps its because your main impact was near the hood and not the front crumple zones, hence the sensors didn't go off? *i'm just speculating*
Any auto techs in the audience? Correct me if im wrong.

Ford will give you the standard runaround on this one.

See, your car was (for the lack of a better word) fortunate to pretty much slide underneath the bed of the F350 ( I assume, mind you). Had you hit a smaller vehicle, or a truck that has a bed a bit lower to the ground, your airbags would definetly had gone off.

Now, the crash sensor on most vehicles sits right front center, just above the top of the bumper. Heres a photo of a sensor from a Mazda 3 (ripped off Google images.)

The Ford you were in was just the right size for for crash sensor to miss being tripped, thus deploying the airbags. It looks like from the photos that the majority of the damage is to the top of the hood, wheras there is limited bumper damage. Not nearly enough direct impact to the bumper to trip the airbag/crash sensor.

Now, you may ask, what factors go into setting off an airbag?

First, the laws of motion come into play. Your car, and ultimately you the driver/passenger have a lot of momentum that needs to be brought down to nothing when you get into an accident.

Essentially, your airbag sensor monitors deceleration at the point of impact on the crash sensor and makes a split second calculation (20 to 30 milliseconds that is) and if the vehicle is over the threshold speed of 15 KMH it then deploys the bag which inflate, and deflate in under half a second.

Now, why 15 kmh? Striking a solid barrier at 15kmh and striking a parked car at 45kmh are the same thing.

Why? Well, a solid barrier will not absorb much impact. The force of the impact will be transferred to the vehicle and then the driver whereas, a parked car will absorb much more of the impact from the pushing that is induced from collision.

So your friend should be prepared for disappointment in this instance. The circumstances were not "ideal" (lack of a better word) for deployment.

(with some ripping off from wikipedia)

Last edited by spacemoose; March 17th, 2008 at 17:13..
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