It’s a crash sensor - cite: http://www.howstuffworks.com/airbag.htm
Hmmm…I’m almost scared to post links found in Google after DDG’s pitting.
I was in an accident in September; the front of my car hit the side of another car (which was making an illegal and utterly unexpected left turn, I might add) at about 35 mph. The airbag deployed on impact.
First off, that thing is fast. I did not actually see it come out; one second it wasn’t there, and then WHOMPH–it was full out in front of me. There was a lot of dust filling the car and making me cough, and I got out as soon as I could.
I’m on the small side, about 5’4", but the airbag did not hit me in the face. It shoved my hands away from the steering wheel so hard that my wrists were badly bruised; the left wrist swelled up so that I thought it might be sprained or broken (it wasn’t). I also had some mild red abrasion marks on my forearms that faded by the next day or so. However, those were the only injuries I had from the accident.
According to my owner’s manual, there is a slight risk of injury from glasses. In the tradition of stupid user-manual warnings (e.g. Do not attempt to raise your vehicle’s window when anyone’s hand or arm is in the way.) it goes on to say that you should still wear your eyeglasses to avoid causing an accident due to impaired vision.
You heard it here at the Straight Dope, kids.
Oh, and thanks for all the replies! It sounds like the usual vehicular adage applies: Your Mileage May Vary. 
Remember, the seatbelt will keep you about 10x safer than an airbag would.
Both my kids took an advanced driving course this summer that is a shortened version of what police get. (How to drive and control/brake/dodge-other-vehicles, etc at high speeds, things like that)
The instructors really stressed the importance of 9/3 hand position. They claimed someone had recently been killed when an airbag drove the driver’s thumb into an eye and part of the brain. No documentation, and maybe it was just for shock value, but it made an impression on the people taking the course.
This whole 9/3 hand position thing is 100% new to me (till reading this thread). For me it’s always been 10/2.
Is the new position recommended strictly due to airbags? Also, while 9/3 may save some inury if your airbag deploys it would seem to me you have somewhat less control over your car from that position. 10/2 allows more movement of your arm to turn the wheel (or so it seems to me).
In high school my sister drove my mother’s car head-on into a sea wall, causing the airbag to deploy. It saved her from serious injury or death, but caused major bruising on her face and upper body, and split the skin on the inner part of her upper arm, resulting in a thin scar about five to six inches in length.
9/3 hand position is currently being emphasized VERY heavily by the state of Illinois in their driver education material. At least, it was when I had traffic school a month ago. The lady must have told us ten times not to drive at 10/2. As someone who drives at 9 and cigarette anyways, not important to me.
FWIW, the new focus in Illinois is apparently due to an off-duty downstate cop who got both his arms broken by his airbag in a crash. No cites, that’s just what the traffic school instructor said.
Maybe I should make a GQ- has anyone ever learned anything useful in a state-mandated traffic school? Besides the answer to the question “how can I quickly waste $125 and at the same time keep my insurance from skyrocketing?”
Odd…never heard a thing about this till now. I believe what you’re telling me but I just figured the info would have trickled down to me by now.
Also, one had better inform the car manufacturers. I recently bought a 2003 car (first year it’s been for sale too) and the steering wheel has an expanded part of the wheel at the 10 & 2 position…presumably for better comfort (or to aid or encourage the driver to keep their hands in that spot…couldn’t really say myself). FWIW my car is air bag central with the things all around (front, side impact, head curtain). I would think they’d move those bumps to the new ‘preferred’ position (and maybe they will and just need to get a few tens of thousands of steering wheels off their shelves first).
I wonder how many of the “punched in the face” posters are short or drive close to the wheel, vs. how many “it was nothing” posters are tall or drive far from the wheel.
Being 5’2" and a close driver I am told it is not advisable for me to drive a car with airbag engaged. My current car doesn’t have one.
My wife is around 5’ 2" and was in a low speed (<30mph) crash about 6 months ago, and was beat up by the airbag (she was wearing her seatbelt). Injuries included: Burn and extensive bruising to left arm, laceration on the inside of her mouth where her lower lip was forced over her lower teeth and other soft tissue injuries to her face and chest. None of it was serious but it was very painful.
Re: Hello Again: my sister is maybe 5’3’’, 5’4’’.
I’m 5’2" myself and airbags have always made me leery. Then I married someone who works for GM’s Product Allegation Team, who handles all of the warrenty phone calls for airbags and there have been some nasty horror stories. If you’re holding the wheel at anywhere other than the 9 and 3 positions, with your thumb wrapped around the wheel, the 200MPH blast can rip them right off. If you’re not wearing your seatbelt, the airbag can blow you right out of the car. The airbag computer (SDM) calculates rate of decelleration, not strength of impact or speed the car is going and old air bags used rapid combustion, but not anymore. It’s all compressed air now.
However, the funniest story I’ve heard regarding an airbag doesn’t include an accident at all. As a matter of fact, it was a technician who was changing the interior carpet. He was stretched over the front driver’s seat, upside down to access the carpet in the front passenger seat, and leaning on the steering wheel for support. The key was in the on position, engine off, so that he could listen to the radio. When the technician pulled up the carpet and started to clean the area, he took out the SDM and tossed it out the car door. Problem: He didn’t unplug the sensor and the airbag went off with all 200MPH of exploding pressure right to the poor fellow’s groin. All accounts say that he was unconscious for 20 minutes.
Just had to share that. Burns and bruising is common, but preferrable to being spread out on your hood like a carrion buffet any day, IMHO.
I was in an accident two years ago where my airbag deployed. I wasn’t traveling that fast but hit a large curb (long story) and kind of flew through the air. My car landed nose down in a shopping store parking lot. I will also note that I wear glasses, am 5’6 and am a close driver. My glasses were knocked off of my face, scrapping along side of my face, and were knocked into the back seat of my car. My left thumb was dislocated due to the 10/2 position. I also had numerous brush burns on my face. I was also wearing my seatbelt and had some bruising from that. It took a while for the bruising on my face, as well as the burn marks to go away. The one thing that shocked me, as others have mentioned, is that the car instantly filled with smoke. So much smoke (which I didn’t know would happen) that it was almost as if a lit cigarette had caught fire somewhere in the vehicle.
Sorry for the continuation of the hijack, but the “rule” as I learned it 20 years ago was “10 & 2 for comfort, 9 & 3 when you need more control.” In other words, when driving on snow or ice, or at excessive speeds (not that anyone should), or at any other times when driving conditions are risky, 9 & 3 allows you to keep better control of the car.
for “hello again”
i was among ones who felt nothing, am dead average height at 5’ 10"
A relative of mine, who has been in three such accidents where she hit the airbag, claims that she does not remember anything, but in two cases she did get bruised/abraded on her face.
For those of you with children, a warning from the CDC about airbags:
"Airbags and Children
Even in a slow-speed crash, the force of a deployed airbag can injure or kill a young child. Riding in back eliminates children’s risk of injury from front passenger-side airbags. Children 12 years and younger should always ride in the back seat, the safest part of the vehicle in the event of a crash."
http://www.cdc.gov/ncipc/duip/spotlite/chldseat.htm
Please drive carefully.
What does it feel like when your airbag goes off?
You underpants get really squishy.