Question about airbag deployment

I have a '96 VW Jetta with dual airbags. Naturally, the driver’s side airbag is under the steering wheel cover in the middle. I’ve always wondered - perhaps too often while I’m stuck in traffic - what exactly would go down in the fraction of a second during impact.

You see, the cover on the steering wheel with the big VW logo on it is rather big, and more often then not my arm is hanging in front of it while driving. Where is the big plastic cover going to go when the airbag bursts forth upon impact? It could only flip up or down, and god only knows what damage it could cause if that big plastic chunk of car hit me at the speed of an airbag expanding.

So what gives? Am I sitting directly behind a lethal piece of efficient German engineering? I’m sure this has been addressed, but I know the airbag has to fill incredibly fast for it to be effective at all.

On a side note, what of those stories of children being decapitated by airbags? I know I’ve heard of this, has it happened?

I’ve always assumed it hinges up, yea it’s gonna hit your arms on the way, but that’s better then going though the windshield.

Oh, and airbags (IIRC) are the reason you should now be holding the wheel at 9 and 3, it keeps your arms out of the way.

It depends on how tall you are. Studies have shown that short drivers (5’3" or less) who move the driver’s seat forward are at significantly higher risk for injuries caused by the cover of a deploying airbag:

I don’t know about your particular car but most steering wheel airbag systems are designed such that the airbag issues from the middle, splitting the vinyl or leather cover horizontally, like the one pictured in the Wikipedia article. The split piece or pieces remain attached to the steering wheel cover while the airbag deploys, which pushes it away and behind the bag. Similarly, it pushes hands and arms to the side, assuming that they’re not being held across the wheel. If you are driving “Buick style” with one arm lazily dangling diagonally across the wheel, you might want to rethink that policy; not only is it dangerous if the airbag deploys–probably breaking your ulna and shoving it into your face–but it also offers very little control or range in a critical situation. Ditto with holding the wheel in the two and ten positions, leading to broken wrists; you’re better off holding the wheel at the three and nine, or even lower, which actually affords better control as well as keeping arms out of the way of the deploying airbag. Similarly, smoking (particularly with a cigarette holder or pipe) while driving is contraindicated for very obvious and lethal reasons.

The problem with airbags injuring or killing children and small passengers is a real one. This comes from the problem that in order to offer maximum cushioning the airbag needs to be aimed such that the head is at the center of the bag which minimizes the offset of the impact. With older round bags this gave somewhere around an 18" target, so children and short adults (<5’3"/160cm)) might be caught by the bottom edge of the expanding bag and absorb the impact obliquely, resulting in a substantial vertical force which can cause significant and potentially lethal injury. Aggrevating this is the fact that short drivers and passengers tend to sit closer to the wheel/dashboard, and either wear and improperly adjusted seatbelt or leave the slash portion of the belt behind them due to discomfort. This places them closer to the airbag and thus receive more of the brunt of the inflation impulse while the bag is expanding. Newer two-stage bags reduce the rate of expansion and resultant instantaneous impulse, and some cars have sensors to disable the passenger airbag if it doesn’t detect an adult mass in the seat.

There are also other problems with airbags as well. Airbags deploy in about one twentieth of a second from a pyrotechnic charge that “burns” a cold gas solid propellant (similar to what ejects ballistic missiles out of a submarine), and deflate almost as quickly. It’s likely that if you are ever in a wreck where one is used, you’ll never see it. It does, however, pose a hazard to rescuers and mechanics, and with the advent of side impact airbags, one has to be careful about cutting into the frame. Such extraction or removal should only be performed by someone who has been trained how to safely.

So, airbags are kind of dangerous to passengers, rescuers, and mechanics. Are they worth it? Although the platitude that “airbags save lives” is generally accepted, it’s uncertain how true this is, at least for frontal impacts. Certainly they provide some measure of protection to a 95th percentile human male in a frontal impact sans any other restraint, but it’s questionable that they offer much benefit over existing restraints. The purpose of the airbag isn’t to shield you from impact, but to prevent you from bashing your head into the dashboard or being impaled on the steering column, which a standard three point seatbelt will do most adequately. Most people probably know someone who claims that an airbag “saved my life”, but in virtually any frontal impact where a bag deploys a seatbelt will have already restrained movement. They provide significantly more benefit in oblique or side impacts where three-point belts can’t effectively restrain motion, but side impact airbags are a relatively recent innovation and are only offered on a select (though expanding) range of vehicles, so the emperical advantage of side impact bags has yet to be seen. And as much as (some) automakers may have complained about the expense of installing airbags, they actually make a hefty profit on replacement bags, which presumably compensates them for the regulatory requirement to install them.

You’re better off just not testing the effectiveness of your airbags at all, but since you have them, you should modify your behavior and habits while behind the wheel to minimize the potential risks should an untoward incident occur.


There have been documented decapitations of **unrestrained ** children by airbags. Needless to say, a child’s chances of survival are pretty low if they’re free to be flung around inside the car, or even ejected out an open window, so it’s not like they were likely to survive the accident anyway.

Quickie Cite 1
Quickie Cite 2 (pdf)

It’s worth noting that in medical terms, “decapitation” does not necessarily mean the head has been torn or severed from the body, but can mean the cervical spine has been completely ruptured and detached from the skull.

I heard a report on NPR about first generation airbags being designed to protect vehicle occupants who do not wear seatbelts. This feature made them more dangerous to those of us who do wear them, but it was regarded as an acceptable tradeoff, because the increased safety for unrestrained occupants was far greater than the slight increase in risk for the buckled in ones. Later generation airbags are better at protecting both restrained and unrestrained passengers.

Airbag deploying at 3000 frames per second. It looks like there’s a hinge.

Oh my god. It has a mushroom cloud. No wonder it is so dangerous.

We have done this a lot (I just did a search to find my posts on the topic, there have been a bunch.)
Here is a post on the effects of being in a wreck with an airbag In the same thread Postcards had the best advice about hand placement

Here is a thread dealing with the after effects of a bag deployment Post #11 gives a description of the timing involved in a deployment.
Here is a thread abot airbags and kids

Totally staged, totally fake, but really funny

Well, from watching that video and from what I’ve read it seems it’s common for the cover to split at the middle and the airbag to come out of that opening. Still not sure if that’s the case with my car, but I scooted my seat back a little and I’m grateful that I’m not short. Thanks for all the responses, I’m surprised to get such a wealth of information on the subject.

I followed your link. That is a pretty old article. Published in 1995. They have made changes on how airbags deploy because of the results of studies like the one you reference. It would be interesting to see studies of newer airbags to see if they have corrected this problem.

I can’t speak for all car makers, but in the case of Volvo the answer is yes. if the seat (either seat) is within 4" of its forward most position the airbag (on that side) are depowered, the steering column is set to collapse with less force (driver’s seat), and the seat belt pretensioners are adjusted.
Very sophisticated system.