Airbags and Global Warming

Back in the early 90s, I worked for TRW on a project to develop new technology for airbag sensors. The airbag sensor is the device in the car that decides whether or not to fire the airbag. Obviously, this is a pretty important, potentially life-saving decision. False negative … someone might die. False positive … someone might get unnecessarily injured by the airbag, not to mention the cost of reloading, which was about $2000.

The goal of the project was to migrate from mechanical sensors in the bumpers to electro-mechanical sensors under the gear shift to save wiring cost and improve reliability. An HC11 Motorola processor with a built-in accelerometer and A/D was used to measure the deceleration. The processor would evaluate the acceleration data and decide whether or not to fire the airbag.

Sounds simple enough. Since the integral of acceleration is velocity, add up the acceleration data and that is your change in velocity. The greater the change in velocity, the more likely a crash worth firing the airbag.

The guys in Michigan crashed up several different classes of cars to provide us with raw acceleration data files. Some of the raw data files had names like “30 MPH 50 lb Pig Left Front”. I can only imagine what they used to get this data 😮 . In any case, we had to run this data through our algorithm and make sure the airbags fired on real crashes but not on the others.

Easier said than done.

As it turned out, hitting a 50 lb. pig at 30 MPH is a pretty decelerating event. In the short 30 milliseconds required to make this decision, the algorithms had a hard time deciding what to do correctly.

Airbag Tough Call

It was only after 60ms or more that the algorithms started to reliably distinguish between a real crash and roadkill.


Airbag Misfire

The critical issue was this … the timeframe was too short. There was no reliable way to differentiate all the possible “fire” scenarios from the “no fire” scenarios with just 30 ms worth of data. You just have to get more data. As it turned out, they redesigned the airbag to inflate faster, thereby allowing 60 ms to make a decision, which was just enough time.

It seems to me that we’re in the same boat with Global Warming.

We have a few decades of temperature data for an Earth that is 4.6 billion years old. Looking within those few decades, it looks like we might be heading for catastrophe.

Last 160 Years

Or, it might just be a normal temperature cycle.

Temp Last 160,000 years

Just as with the airbag sensor, we don’t have enough data to make a reliable decision one way or the other. And just as with the airbag, the cost of being wrong is great. False negative … we experience catastrophic climate shifts. False positive … we unnecessarily impose costs upon ourselves and developing countries that can cause social catastrophe.

Personally, I don’t know which is the right answer. And I don’t know how anyone else can know with certainty that they have the right answer. I wish that both sides in this discussion had a little more humility and they would acknowledge that they don’t know more than they do know. And that they could be wrong.

Or maybe these experts are just like the airbags … full of hot air.

harry the ASIC guy

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3 Responses to “Airbags and Global Warming”

  1. Brad says:


    I agree that the data to support global warming is suspect. It is pretty obvious that the earth is warming but we really don’t know the main cause.

    I think we would all be better served if we focus on eliminating pollutants in our air and water that are proven to harm humans and the environment like carbon monoxide, mercury or lead. If we reduce these real pollutants then we will probably also have a positive impact on reducing greenhouse gases.


  2. harry says:

    Two more articles I found regarding the Airbag Sensors in case you are interested:



  3. Arn says:


    What makes you say that the data to support global warming is “suspect”?

    ~99% of all scientific documents support the idea of global warming and in “all” cases co2 and other greenhouse gases are understood as the reason.

    ~50% of all political documents (including news and other types of mass media) does NOT (or rather did not*) believe in global warming or at least not that it is caused by humans.

    * I say did not since it seems like mass media has started to understand that it’s true now when mr Bush (and his supporting companies) isn’t denying it any more (now he’s just not doing anything about it even though he has confirmed that it’s a fact).

    Are you saying that you believe more in political arguments than in scientific reports – or why are you saying it’s suspect?

    However – I do agree that there are many other pollutants that the current government (and many of the previous governments) have done their best to ignore. US lags far behind the rest of the developed world when it comes to regulating extremely dangerous chemicals (in childrens toys and many other day to day items).


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