HEAD injuries are the major cause of death and serious injury in car accidents in Australia and place an enormous toll on not only the individuals and families concerned, but the entire community as well.

Hospitalisation, treatment, rehabilitation, ongoing care, these are all costs that incur as a result of serious brain injury.

Airbags play an important role in avoiding the enormous trauma and expense associated with serious car crashes.

They may not always save a life and should not be viewed in isolation when it comes to purchasing a car.

Independent crash test performance, structural integrity, fitment of seatbelt pretensioners and anti-lock brakes are just a few other items to consider.

But airbags give you a great chance of survival.

They're called supplementary restraint systems (SRS) in Australia because they're designed to go off with less force than in countries like America, where seatbelts aren't compulsory.

That doesn't make them any less effective - in fact, they're better than American-style airbags because their "softer" deployment reduces the risk of airbag-associated injury (like severe whiplash).

So how do they work? In a major accident, electronic crash sensors will send a signal to a control unit telling it to fire the airbag's built-in inflator and send the bag hurtling out of the steering wheel hub (for the driver) or dashboard (front passenger).

It all happens in a split second - literally.

The crash sensors need 15-20 milliseconds to decide whether the accident is serious enough to warrant deployment.

At the 25 millisecond mark, the airbag will split its trim cover and begin to inflate.

By 45 milliseconds the airbag should be fully inflated, just before the seat-belted occupant is expected to hit the bag.

Once the airbag and head make contact - at about the 60 millisecond mark - rear air holes begin the deflation process.

It's all over in less than a blink of the eye.

GOLDEN RULES

Make sure your next car (new or used) has, at the very least, a driver's airbag.

Not every airbag is the same.

The bigger the better.

When comparing cars, check on the size of the airbags (measured in litres).

You might get a surprise on the differences.

Never put a child restraint in the front passenger seat where an airbag is fitted.

If the airbag goes off, it can cause death or serious injury.

Always wear a seatbelt and make sure everyone in the car is wearing one.