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The evolution of airbags
How to recognise your last line of defence

Fast cars might be attractive, but sitting within hundreds of kilos worth of hurtling metal is no fun if you've got nothing between you and what you crash into. Seatbelts are essential, but airbags are your last line of defence.

Airbags aren't as simple as strapping yourself in. They're a complex technology, and if improperly understood can cause as much injury as the crash itself, sometimes even killing children with their deploying force. We've come a long way from such basic systems, though, and today's airbags are increasingly intelligent. That also means that they need to be understood thoroughly, and such knowledge should influence the car you choose to drive. What's more, depending on the age and the brand of vehicle you're driving, you could have one of several types of front airbags – all of which have different benefits and risks.

These days, many passenger cars are equipped with sensors that identify children and very small adults and deploy the airbag with less force or not at all. This doesn't mean it's alright for children to ride up front, but it does mean fewer risks. Some automakers are taking things a step further by designing airbag systems that not only change the force that the airbag deploys with, but also the size and shape of the airbag. These technology advances are all part of an effort to improve airbag safety and benefits.

Protect the child
While safety experts and automakers agree that the safest place for any child aged 12 or under is the backseat, they recognise that some drivers do allow children to sit in the front seat and set out to study the potential injury to a child or small adult when a front-impact airbag deploys. After studying different types of airbag deployments, researchers concluded that airbags in older vehicles pose the greatest risk. A recent American study in the Archives of Paediatric and Adolescent Medicine found that children had a 14.9 per cent chance of serious injury from airbag deployment in a 1997 model year vehicle or older, versus a 9.9 per cent risk in a vehicle model dating between 1998 to 2001. Later model vehicles were not studied. The older vehicles came equipped with first-generation airbags, which could harm and even kill children and very small adults, especially those not wearing seatbelts, due to the extreme force with which the airbags deployed.

Interestingly, children older than 12 years may also be at risk of injury when a front airbag deploys, regardless of their height or weight. A June 2005 study conducted by medical researchers at Oregon Health and Science University concluded that young teens between 13 and 14 years were also at risk due to their lack of bone density and muscle mass. Critical changes in body composition occur during puberty, and as a result the study found that teenagers between 15 to 18 years could benefit from an airbag deploying in the event of a collision.

Stages of deployment
As airbag technology progressed, automakers began to develop methods to reduce the deployment power of airbags based on the size of the occupant. By the early 2000s, some automakers introduced these new airbags, calling them 'advanced,' 'smart,' 'dual stage' or 'multi-stage.'

These airbags were developed to reduce the risk of airbag-related injury or death to children and small adults by either deploying with less force or not at all, depending on the situation. Sensors, usually located in the seat and seatbelts, sent signals to the vehicle's computer providing information such as the weight and seating position of the occupant and if he or she was wearing a seatbelt. In the event of a collision, the computer then made a split-second decision on whether to deploy the airbag at full force, reduced force or not at all.

Unfortunately, in the earliest versions of advanced airbags, the systems didn't always sense the occupant accurately, effectively fooling the computer. Some owners complained that their vehicle's front-passenger 'airbag off' warning light came on whenever a small adult was in the seat, or would intermittently turn off depending on the person's sitting position. Other owners noted systems were so sensitive that the sensors would deactivate the airbag if a seat cover was installed or a towel tossed over the seat. In addition, hard braking or swerving could throw the front passenger off balance and cause the airbag that the sensors chose to deactivate during the moments before an accident.

Some automakers take the technology one step further. Mercedes-Benz and BMW, for example, have sensors that can identify a child car seat on the front-passenger seat and suppress the airbag in a crash. Jaguar's Adaptive Restraint Technology System (ARTS) uses ultrasonic sensors to identify when occupants are out of the typical seating position and either reduce the force or even suppress the airbag altogether.

Both General Motors and Ford have introduced new designs for their front airbags that not only deploy with less force but in a smaller size, depending on the size and location of the occupant. In real world situations, sensors determine the size, shape and force that the airbag should deploy with, or if the airbag should be suppressed completely, within milliseconds. General Motors' 'dual depth' system uses sensors to look at the force of the collision in real time, as well as the weight of the occupant and the position of the seat. The vehicle's computer then determines the appropriate size and force of airbag deployment. GM uses several dummies to test the system to ensure the airbags themselves pose no risk of serious injury. In the driver’s seat, engineers place a small dummy leaning on the steering wheel – the position it would be in if not wearing a seatbelt. In the passenger seat, they use a dummy representing the average-sized ten year old in several unrestrained positions.

Ford's dual-depth system uses weight sensors that place passengers in five different weight classes, varying the size and force of the airbag accordingly. On the driver side, the system uses the seating position to change the airbag deployment and collapsible steering column, depending on the person's size. For a smaller occupant, the system makes the airbag smaller by routing some of the gas that would go into the airbag during a larger deployment into the instrument panel. This way the airbag is smaller and softer and more appropriate for a small-statured occupant.

Lexus has developed the SRS twin-chamber airbag, which deploys in a way that creates a depression in the airbag's center, dispersing the energy throughout the occupant's upper body. This is an advantage over a single-chamber airbag, which often places the force on a specific area of the body, increasing the risk of injury.

The bottom line
Regardless of how advanced airbags become, one thing is likely to remain the same: the recommendation that children under 13 ride in the backseat. After all, technology can only work within, not eliminate, the laws of physics.