This article talks bout the unintended consequences of the stronger materials used in modern vehicles.
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Whoever wrote the article knows little about air bag systems - they do not use pressurized gas canisters, and I doubt if an air bag can inflate with enough force that "rescuers can be blown from cars when airbags suddenly inflate," especially if the power has been cut to the air bag system for more than 30 seconds. I would imagine that fire departments cut the battery cables if they have to extricate a crash victim.
"Ray O" wrote in news:spWdna4eC5MSanzanZ2dnUVZ snipped-for-privacy@comcast.com:
The error is understandable.
The actual source of inflation is not something they like to advertise: a charge of sodium azide, the same stuff used to detonate high explosives like TNT. Essentially, you've got part of a bomb in your steering wheel.
That is true, generally one of the first things they do is cut the ground cable. If a vehicle has been in by far the most frequent type of accident, a frontal collision, the SRS will have been deployed in any event. Being aware of the high voltage system wiring in today hybrids is more of a concern for rescue workers it seems.
Typically, the decision to deploy an airbag in a frontal crash is made within 15 to 30 milliseconds after the onset of the crash, and both the driver and passenger airbags are fully inflated within approximately 60-80 MILLISECONDS after the first moment of vehicle contact. An airbag must be able to deploy in a matter of milliseconds from the initial collision impact. It must also be prevented from deploying when there is no collision. Hence, the first component of the airbag system is a sensor that can detect head-on collisions and immediately trigger the airbag's deployment. One of the simplest designs employed for the crash sensor is a steel ball that slides inside a smooth bore. The ball is held in place by a permanent magnet or by a stiff spring, which inhibit the ball's motion when the car drives over bumps or potholes. However, when the car decelerates very quickly, as in a head-on crash, the ball suddenly moves forward and turns on an electrical circuit, initiating the process of inflating the airbag.
Once the electrical circuit has been turned on by the sensor, a pellet of sodium azide (NaN3) is ignited. A rapid reaction occurs, generating nitrogen gas (N2). This gas fills a nylon or polyamide bag at a velocity of 150 to
250 miles per hour. This process, from the initial impact of the crash to full inflation of the airbags, takes only about 40 milliseconds. Ideally, the body of the driver (or passenger) should not hit the airbag while it is still inflating. In order for the airbag to cushion the head and torso with air for maximum protection, the airbag must begin to deflate (i.e., decrease its internal pressure) by the time the body hits it. Otherwise, the high internal pressure of the airbag would create a surface as hard as stone-- not the protective cushion you would want to crash into!
"Tegger" wrote in message news:Xns9A674BC616A39tegger@207.14.116.130...
I watched a demo of airbag deployment in a dealer parking lot. Very impressive, everybody jumped when it went off. It's a small bomb inside your steering wheel.
How would they cut the power? To do that, they have to get under the hood or back seat (some batteries are under the back seat or in other locations) to cut the power.
The time a called the fire department to the scene of an accident where a car had hit a light pole, a fireman stuck what looked like a pair of bolt cutters with very wide jaws into the grille and cut the hood latch, opened the hood, and cut the battery cables. This was well before airbags appeared in cars, so cutting the power must have been SOP for a while.
A major supplier of air bag inflators is Morton Thiokol, maker of solid fuels for missiles, rockets (including the now infamous Challenger rockets), and ejection seats.
I am not familiar with Chrysler air bag systems, but I don't think that any kind of pressurized canister would be a very good solution because the squibs used in air bags react much more quickly than any valve or canister piercing mechanism and probably cost a lot less than a mechanical system. Also, argon is an inert gas, so I wonder if it would interfere with the combustion of the air bag squib.
"Ray O" wrote in news:8cydneniEdVP1H7anZ2dnUVZ snipped-for-privacy@comcast.com:
Sodium azide contains its own oxygen supply; argon would have no effect on it.
I'd be surprised if compressed gas was ever used in an SRS system.
Since early airbags were required by federal law to explode at over 200mph (in spite of automaker concerns), I'm thinking compressed gas would have too much inertia to inflate the bag that quickly. The violence of a sodium azide explosion would be more effective. Plus a compressed gas canister would be both larger and heavier, and require more complex controls than a simple sodium azide charge.
There are a lot of folks that do not understand the workings of the system. Many think that the SRS bags stay inflated based on what the see in movies etc. LOL
How true! I looked at quite a few vehicles where people claimed that the airbags were defective or didn't deploy completely because the air bags were deflated or didn't completely fill the front of the car.
I am still not sure why. Some concern is OK but considering the first thing a Prius does after it deploys the airbags in a wreck is kill the 12V power to the system main relays which disconnects the HV battery from the rest of the car it should be a non issue.
"Daniel Who Wants to Know" wrote in message news:Ql%Ej.33177$TT4.1494@attbi_s22...
Rescuers probably cut battery cables to make sure that there is no possibility of sparks if they cut a wiring harness, and rather than rely on a circuit that may have been damaged in a crash, they take no chances.
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