The importance of side airbags and head protection in modern cars

This lifesaving technology offers unprecedented protection

The crash test in this vieo is happening at just 29km/h. And without the precise, head-protecting airbag choreography, even slow crashes like this one are killers.

To emphasise this point: if you hit a pole, sideways, at 29km/h or more, and if your car lacks side curtain airbags (or head protecting side airbags built into the seat) - you will probably die.

This is why experts at ANCAP (Australasian New Car Assessment Program) and its crash-testing counterparts around the world conduct the so-called 'pole test' at 29km/h - it represents the thresshold of survivability.

In the ANCAP pole test the vehicle rides a speed-controlled sled and impacts a rigidly mounted 250mm steel pipe at precisely 29km/h. The pole, does not move, is exactly aligned with the driver's head (in this case a crash-test, or hominid, dummy overloaded with accelerometers).

The crash, or at least the part of it that will kill you, is over in just 40 milliseconds (0.04 seconds). To put that into perspective, the blink of an average human eye lasts 200 milliseconds (0.2 seconds). So the potentially lethal part of the crash is five times faster than the blink of an eye.

The fact that a protection system able to spring into action inside this somewhat anorexic window of opportunity has been designed and perfected, not to mention made affordable, is nothing short of a miracle.

Breakneck speeds are involved. Shortly after a side impact takes place, the curtain bag receives an electrical pulse from a crash sensor mounted in the vehicle. A detonator explodes, then an unstoppable chemical reaction not unlike that in a solidfuel rocket motor, commences. Solid fuel in the bag rapidly converts to (harmless) nitrogen gas. Result? The airbag bursts down from the roof at more than 300km/h. It has to be brutally quick just to get between your head and the crash, in the brief window of time available in the circumstances.

Curtain airbags don't just protect you from poles, which are typically struck only if control is lost and the vehicle is sliding. They also protect you in side-on crashes at intersections - and it's worth remembering that 50 per cent of all road trauma occurs at intersection. They’re also a barrier against ejection in a rollover, where the side-to-side 'flailing' motion of the passengers often sees them partially ejected through the window aperture even if a seatbelt is worn.Finally, curtain airbags also protect against intrusion – preventing things like high-speed broken glass, crash debris and foliage from entering the cabin.

The first full-length curtain airbag debuted in the 1998 Volvo S80 - Volvo's then-most luxurious and largest car. Twelve years later they’re affordable, and available in a wide range of new and even some used cars. (Incidentally, this is fairly typical for the speed with which safety innovations migrate through from the top end the market into cars average buyers can afford.

Every car on the market with a five-star ANCAP safety rating offers some form of side airbag with head protection - either a curtain or a seat-based airbag.

Bottom line: If you’re ever in the unfortunate position of the crash-test dummy in this video, curtain airbags are the difference between a big shock and standing at the roadside shaken, but with your marbles intact to the point you can fill out the tow-truck paperwork, and being rushed to hospital with a brain injury and a very uncertain future.

The vehicle in this video is a 2009 model Mercedes-Benz Viano. The crash test took place in Melbourne's Autoliv laboratory in Melbourne in the second half of 2009. Aceing the test (which the Viano did, scoring a significant 32.5 points out of a psssible 37 - more than adequate to earn its five-star rating) meant that the Vito van which shares the same basic structure as the Viano was the first five-star light-commercial van in the country.

However, it's worth remembering the Vito's side curtain airbags are available as an option only, costing several hundred dollars. Statistically, very few buyers opt for the curtain airbags - and we're told the Mercedes-Benz commercial vehicles operation in Australia is currently considering fitting the curtain bags as standard to the Vito, despite the upward pressure on price inherent in this move.

So, if you're buying a new vehicle there's a message in this situation - make sure the five-star rating in the advertising actually applies to the specific model you're buying, with the options you have elected to purchase.