Why didn't my airbags deploy?

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Why didn't my airbags deploy?

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Looking at a passenger car in a crash involving the front of the car, mostly on the right side, but it is all focused on the front of the car. The airbags didn't deploy. I'm trying to figure out why not. In the owner's manual, it says:
The airbag system is designed to deploy when the Occupant Restraint Controller (ORC) detects a moderate-to-severe frontal collision, to help restrain the driver and front passenger, and then to immediately deflate.
I remember seeing something in another car's manual I had that talked about hitting a wall or another car at certain speeds. What do they mean by "moderate-to-severe frontal collision?" How fast do you have to be going to deploy an airbag?
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DPatrickRyan
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Re: Why didn't my airbags deploy?

Post by DPatrickRyan »

There are two answers: "it depends", and "because it wasn't appropriate" (probably).

Severity (or, more precisely, shape of the crash pulse), orientation, seat belt use, seat adjustment, and occupant stature are some of the major factors that govern air bag deployment. How fast you're going, or even the total collision severity (Delta-V) can be completely irrelevant to the airbag deployment decision. A "normal" collision duration might be 80-150 milliseconds, but typically the air bag deployment decision has to be made roughly 30 milliseconds in. The total delta-V therefore is not, and cannot be, a criterion for air bag deployment. You might, for example, have a severe impact that started with a relatively long period of lesser severity before the acceleration spiked suddenly (e.g. a pole impact, or an underride). In such a situation, the large accelerations might occur too late to indicate safe deployment, since the occupant might already be too close to the air bag. You might also have a collision with lots of front end damage, but in which the PDOF (collision force orientation) was predominantly lateral (to the side).

Every case is different and a situationally complete analysis needs to be completed in order to determine whether deployment was appropriate or not. I (obviously) don't know what your reconstruction background is, but if you're not able to determine and understand such things as the longitudinal component of delta-V, you shouldn't be attempting to answer the question as to why the air bag did not deploy. I don't mean any insult by that - it's simply not a skill set you have, and you should refer the matter to an appropriate expert rather than get eaten alive on the stand later.
D. Patrick Ryan, P.Eng. - Graham Ryan Consulting Ltd.
#34, 11410 - 27 Street SE Calgary, AB T2Z 3R6
Phone: (403) 290-1150 Fax: 290-0659 Cell: 651-8340

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