What exactly expires w/an airbag?

I've read in other posts that MB has extended life 15yrs from manufacture date. Since I have an 1986 300E, however, my time is nearly up.

Does the airbag itself become brittle. What might it cost to fix my expiration problem -- any ideas?

Thanks,

Steve

The Airbag deploys via ignition of a substance - typically Sodium Azide. (See http://www.howstuffworks.com/airbag1.htm for a full article). The ignitor and Sodium Azide MAY degrade with time, and the Accelerometer/sensor MAY become unreliable with time. Life span of airbags is a valid engineering concern, but is also probably driven by legal liability issues. I understand a replacement bag is about $1000! Mine expires next year - I am still debating my options.

[Edited by JCE on 05-04-2001 at 05:47 PM]

when we say it can become unreliable, does it mean unreliable by NOT deploying when it is needed, or that it can deploy any time?

i would prefer the former rather than the latter.

All systems have a failure rate, airbags included, regardless of age. The greatest failure probability I have read about on airbags, new or old, is failure to deploy or to deploy adequately. There are occurances of the bag deploying when not wanted.

This is part of the arguments that occured in engineering circles in the early 70s - what was an acceptable failure rate. the other arguments were "how do you limit the explosive noise from the airbag to levels below hearing damage thresholds", "How long do you certify them to meet your failure rate criterea", "What do you do with the hazardous waste from deployed air bags" "What hazard do these pose to auto dismantlers, children playing in abandoned cars, etc." "What about short people, people with glasses, children, etc", "What happens when people rely on the bag and stop wearing seatbelts"?

I always rely on my seat belt and pretend the air bag isn't even there. I am leaning towards installing a 5 point belt system instead of the airbag after it expires, if California's extreme "Papa knows best" laws allow me to do such a modification.

steve7 the ignitor on the back of the drivers air bag is easily replaceable. you can buy the pt from your dealer.if you are handy you can disassemble the air bag and replace the ignitor.the other one on the passenger side i'm not sure if you can purchase that one or not.also i think that there is an expiration date on the door post i think it's only 10 yrs if i'm not mistaken.....mb_buddy

Thanks for the input everyone.

John, while you write that degrading materials over time is a real concern, you also suggest that the expiration date may also be driven by liablity concerns. Are you then suggesting that airbags are likely functionable for sometime after their expiration date? Afterall, $1000 is a good deal of money for an older car!

Steve7

Steve:
The airbag's ability to function probably does not end on the expiration date. Almost 100% of the time a safety factor on life span is built in by the engineers that design the system, and that safety factor is usually enhanced by corporate attornies, in my experience.

If the chemists and engineers feel that the device is good for, say, 10 years, they may certify it for 10-25% shorter time. The lawyers, working from the standpoint of liability aversion, may subtract another 10-25% from the life span of the device, on the theory that the engineers could have been wrong about the expected life span.

It is really all about probability. A new airbag (or anything else, for that matter) has a very small but real probability of not working when needed, or going off at the wrong time. As it ages, the probability of failure increases, along some "average" curve. The fact that there is an average curve does not garantee that a particular airbag will respond like that curve! Some devices may last 25 years - 10 years longer than expected by the engineers. Others may have been 'dead' in our steering wheels since day one, and we will never know when it 'died'.

I am not one to bet my life on used or expired safety equipment. I plan on replacing the stock belts and tensioners in my car next year (air pollution and dust particles can degrade nylon belt material). I may also do the airbag, as my car is in top condition with low miles, but I do not regard the airbag as my primary safety feature.

To me, the primary safety devices are the condition of the car's tires, brakes, and suspension, and overall mechanical reliability (coupled with my ability to drive ;) ) The secondary line of defense is the structure of the car and the seat belt system. My last line of defense is the airbag. I may choose to spend $1000 on a driving course that will enhance my 1st line of defense rather than enhancing my 3rd line of safety. Others may choose differently in their priorities.

Sorry to be so long winded, hope this helps. I know that your asking the question helped me clarify my thinking on this pending expense! Thanks for asking!

[Edited by JCE on 05-05-2001 at 01:31 PM]