Unfortunately one can still see motorists, both men and women, who sit too close to the steering wheel. Should an airbag be triggered, it may be too late, the pressure of the airbag, together with the restriction of the backrest, can be life threatening. Here are two thumb-rules: 1. Keep at least 25 centimeters of distance between the upper body and the steering wheel. 2. With the backrest not too sloping, one must be able to grip the upper part of the steering wheel and at the same time, the shoulders should be touching the backrest.

Of course, one must be able to press the pedals to the floor. Thereby, the knees should be slightly bent. The upper edge of the headrest should be above the level of the eyes. Front seat passengers should try to find a comfortable position as far back as possible. Both should make sure that the seat-belts are always quite snug-fitting, and of course, they should not be twisted anywhere.

The air bag belongs unambiguously to the group of passive safety measures, because it reduces the consequences of an accident. It consists of a folded air bag in the steering wheel (figure), the dash board, the seat back, in the edge of the roof, or in the B/C pillar. There are two kinds of steering wheel air bags, a slightly smaller European 60-l version, and a larger, originally American air bag with 80 litres (Full Size). Although the latter was initially designed also for non-belted persons, a safety belt with seatbelt tensioner always forms an inevitable combination with the air bag. In case of seat air bags only registered seat covers may be used. Older air bags should be checked for a prescribed exchange date (e.g., 10 years).

Earlier statistics show the frontal impact as the most common. More recent ones maintain that side collisions are more frequent. Despite the use of seat-belts and and tensioners, an impact with the steering wheel or dashboard can still occur, also unacceptable deceleration of the head can lead to a whiplash trauma. Airbags reduce the danger significantly. In modern vehicles, due to more and improved sensors, (e.g., seat occupancy detection) they are only triggered, when it is really necessary. Indeed, sometimes even child-seats are detected. In addition, the position of the person to be protected, will soon be possible. As a result, the airbag is partially, completely or not triggered at all, this is important e.g., for side-airbags.

The airbag belongs, without a doubt, to the passive safety precautions, because it reduces the consequences of an accident. It consists of a folded air-sack in the steering wheel (see picture 4), the dashboard, the back-rest, the roof edge or in the B/C-pillars. There are two types of steering wheel airbags, the somewhat smaller European version with 30/70 liters (driver and passenger), and a larger, originally American version with approx. 80/150 liters (full-size). Even though the latter was designed for those who were not belted up, the safety system should always include seat-belts and tensioners. Only approved seat-covers may be used if there are seat airbags as well. Older airbags should be tested after the prescribed period (e.g., 10 years), or their replacement is mandatory.

Above 30 km/h and a force of 2 Gs (2 * 9,81 m/s²) of longitudinal or diagonal deceleration, the airbag is completely, or through a second gas generator, partially inflated in approx. 50 milliseconds. However, the air escapes through exactly defined openings, thus determining the shape. In the steering wheel impact-hub and on the passenger side there are mostly complete airbag units with nylon air-sacks, 1 or 2 gas generators and impact absorbers with break-off points built in. Once an airbag has been triggered, the entire system should be replaced.

After more than 100 milliseconds the bag is deflated again so that, e.g., possible rescue measures are not obstructed. From the two sensors up front, two each in the doors and B-pillar and one in the control device, at least two of them must give out a crash signal. Apart from that, a second controller examines the data once again. Nevertheless, it only takes 50 microseconds until the possible ignition takes place. Thereby, as a rule, various impact types are detected and distinguished from other violent vehicle movements.

Paying attention to the airbag warning light is particularly important for the driver. It lights up for a short time when switching on the ignition and checks the entire system. It simulates the triggering without actually carrying it out. Only when the light stays on permanently, is a defect indicated. This should then be repaired as soon as possible, because from this point onwards, a false triggering could take place at any time, without warning.

Modern control devices record all the relevant data during an accident and may be able to transmit, through wireless networking, an SOS-signal. It depends not only on the exceeding of a certain delay, but more on the time-profile, which must correspond to the pattern of a typical accident. The respective crash-sensor can be compared with a weight on a spring, where during the crash, the spring-travel is measured.

The safety measures taken when working on areas where airbags are installed, are of paramount importance. Here e.g., short circuit bridges are used, which prevent a triggering when the connection is broken. In principle, it is not enough to remove the earth cable from the battery when working anywhere near the airbags. The airbag can still be ignited if the on-board electrics break down, through so-called power reserves. This can be due to, e.g., the two relatively large capacitors which are used.

The gas generator built into the steering wheel is, as a rule, no longer connected by slip-rings and carbon-brushes, but through a coiled conductor. When installing, this must be placed in exactly the same way as before because it is precisely adapted to the possible steering wheel rotations in both directions.

As far as airbag technology is concerned, new responsibilities are being placed, not only in the event of a replacement, but also as far as the disposal of vehicles or vehicle parts are concerned. To avoid later accidents, every airbag must be triggered before it is scrapped. After all, pressures of approx. 600 bar are built up. This is why the safety regulations must be implicitly observed, this of course, also applies to the normal storage of the airbags.
This is especially valid for regulations, which can quickly become outdated. Before one can actually dismantle an airbag only 5 minutes after disconnecting the battery, it is recomended that one has a look at the manufacturers information. Also, can one still install an airbag which e.g., has fallen to the ground from a height of 50 centimeters? 08/10