airbags - the cost of inflation

once a luxury life saver, airbags are now fitted to even the cheapest cars. yet do you really need them, are they dangerous and how do they work? jonathan crouch reports

airbags - the cost of inflation

Not long ago, top German motor racing driver Bernd Schneider was hurling his Mercedes touring car around the twists and turns of Europe's most dangerous motor racing track, the 14 mile-long Nurburgring circuit built among the Eiffel mountains south of Frankfurt.

Barrelling down through one of the many chicanes, his car crashed against the kerbing, inflating to his surprise the airbag that Mercedes insist is fitted even to their racing machines. Just what he didn't need at over 100mph in the middle of a forest.

Yet examine the facts and there's an overwelming case for having airbags. There's also, as Herr Schneider found, little reason to fear...

Airbags are compulsory these days in the European market. The airbag concept - a large cushion which explodes from the centre of the steering wheel to protect your head when the car sustains a violent front impact - was originally a European concept anyway. Mercedes-Benz pioneered its development way back in 1967 and little in essence has changed since.

All Airbags Are Not The Same

The fact that your car is fitted with an airbag should not give you a false sense of security. Unlike the 60-litre airbags used in the USA (where seatbelt wearing is not compulsory in some states) the smaller 40-litre `Eurobags` that most cars use here must work in conjunction with seatbelts if they are to be really effective.

As the deployment of airbags has become compulsory on new cars, manufacturers now fit a whole range airbags to protect the driver and passengers. As well as passenger airbags there are now side-impact airbags, curtain airbags and even knee airbags to reduce damage to occupants' legs.

Airbags built into the back of the front seats to protect rear seat passengers are also available. Research has shown however that the front seats move forward in impact and provided back seat passengers are properly belted up, there's little chance of any facial impact.

How Do They Work?

Extremely quickly is the short answer. Typically, an airbag will be fully inflated within 30 milliseconds (0.03 secs) after the point of impact. To ensure that it doesn't go off accidentally, or trigger in minor impacts, a threshold deceleration has to be reached before the sensors activate inflation. In Europe, this can be anything from 12-20mph.

There are few recorded instances of airbags going off accidentally. They're manufactured to military equipment standards, hermetically sealed and designed to last at least ten years. Providing that the triggering mechanism is working properly, malfunctions are almost unheard of.

Manufacturers do warn however, against exposing them to excessive heat (such as would be generated by a blowtorch or welding equipment), ill-advised tampering by DIY enthusiasts (don't) and excessive bashing of the module in the centre of the steering wheel.

Parents must also ensure that rear-facing child safety seats are not placed in the front, should the car be fitted with a passenger side airbag. Use an approved rear safety seat, bearing in mind that very young babies should have a rear-facing, not forward-facing, seat.

Are They Effective?

If used in conjunction with a seatbelt, the answer is emphatically `yes`. The best known evidence is a story of an accident in the American state of Virginia. The two cars involved were both 1989 Chryslers and hit each other head-on at a closing speed of 68mph.

Instead of being killed outright, both drivers survived the crash with only superficial injuries, despite the fact that one of them was not wearing a seatbelt. Recent tests have shown that even at slower collision speeds of 19-31mph, 30% of belted drivers received head or chest injuries in cars not fitted with airbags, a figure which rises to 70% at higher speeds.

Though only 3% of such injuries are likely to be fatal, the remainder often cause disfigurement or debilitation. A permanent reminder in other words.

What Happens When It Goes Off?

There's an explosion no louder than the sound of a paper bag being burst which propels the nylon bag towards your face. Since it's not completely gas tight, it will automatically deflate again within a split second so as not to impair your vision or hamper your escape from the car.

It doesn't hurt - volunteers describe it like being hit with a pillow - and since an airbag distributes the force of impact so evenly, it's unlikely to shatter your glasses. Even if you're smoking a pipe, there's little danger, it's likely that the force of deceleration will have flung it from your mouth.