Auto air bags get smarter

The history of air bags in automobiles is as much a political story as it is a technical one. Because Americans largely refused to use seatbelts and their governments were too cowardly to force them to, said governments then passed the buck on to the car makers, and required them to design systems that would enable occupants to survive a 30 m.p.h. (48 km/h) crash into a fixed barrier assuming no seatbelt was in use.

So a simple and cheap political solution was canned in favour of a vastly more complex, more expensive and less effective solution.

However, air bags are (probably) here to stay, and the way the concept has been promoted, consumers seem to believe the more bags, the better.

We have bags in the steering wheel hub and dashboard for frontal collisions (some cars have them in the back of the front seats for rear-seat passengers too); in the sides of the seats and/or door trim panels and/or door support pillars for side-on ("T-bone") collisions; in the front windshield pillars and/or outward edges of the roof, creating an inflated "curtain" to protect against roll-overs; under the steering column to protect the driver's knees.

To my personal knowledge, the world record for air-bag deployment took place at a press event in Monaco when a Swedish journalist emulated a big bobsled crash on a narrow rock-wall-encapsulated road. By the time he had hit every hard vertical surface in the principality, two frontal bags, two front-side bags, two rear-seat bags and the side curtains had gone "bang"; eight bags in a single-car crash.

He didn't hear much at dinner that night.

Essentially, all air bags operate the same way. Deceleration sensors detect the initiation of a crash. An igniter lights off a chemical reaction that creates a gaseous "propellant," which rapidly fills a nylon bag. The bag "deploys" (a more polite-sounding word than "explodes") into the car, cushioning the occupants from bouncing off something hard and nasty.

Of course, an air bag only stays inflated for a few seconds, resulting in what appears to be a huge condom lying in your lap. If you have smashed into a truck and are now careening down an embankment, your air bag is a spent force – you still need the seatbelt to provide primary and on-going protection.

That said, even deflated side curtains can assist in preventing occupants from being ejected from the vehicle (statistically, the worst thing that can happen in a crash) or by deflecting outside objects such as tree branches from inflicting further damage.

Bags are getting "smarter." Some can detect the weight (or even the mere presence) of an occupant, the seat position (so it knows its proximity to the dashboard), and the severity of the crash, and deploy more or less vigorously, and/or to greater or lesser girth, to ensure the force of the air bag doesn't do more damage than the crash itself.

It is for this reason that shorter people or small children can be in danger sitting in an air-bag-equipped position.

Air bags have other drawbacks. In addition to the collateral damage they can cause, they are highly explosive devices, and extra care is required by car parts recycling depots (a.k.a. junk yards) in dismantling the vehicle.

The deployment is an incredibly precise series of technical steps, which we expect to work perfectly every time, even if the system has not been checked or maintained for years.

There have been some concerns that the chemicals used and created in air bag deployment, notably sodium azide, are toxic or possibly carcinogenic, although I am unaware of any studies than prove that conclusively.

Any crash severe enough to trigger the bags probably makes the car a write-off; in addition to the cost of the bag systems themselves, the deployment thereof almost surely destroys the interior of the vehicle, and the cost of repairing that is almost always higher than the residual value of the car.

Perhaps the biggest drawback is the sense of false security they can impart. While the American National Highway Traffic Safety Administration boasts that some 3,000 lives per year are saved by air bags, a study conducted some years ago by Dr. Leonard Evans, one of the world's most authoritative car crash safety researchers, concluded that an air bag by itself is less than 20 per cent effective in preventing death in a crash, a three-point lap/shoulder belt is about 40 per cent effective, and a three-point belt combined with an air bag is about 46 per cent effective.

So the bag adds only about 5 to 6 per cent effectiveness to a properly fitted seatbelt .

Other studies have put that number higher.

But for sure, air bags are nice to have.

Still, always fasten your seatbelt .

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