How airbags work
- A front airbag system includes a large nylon bag, which is inflated and deflated rapidly in the event of a severe frontal crash. The driver’s airbag is housed in the centre pad of the steering wheel, and the passenger’s airbag, where fitted, in the upper left of the dash.
- The airbag’s deployment is controlled by sensors that detect the occurrence and severity of a crash. When the airbag controller determines that the airbag should be deployed, the system triggers an inflator unit that burns chemicals very rapidly to produce large volumes of inert gas to inflate the bag.
- As the bag inflates, it splits open the covers on the wheel or the dash, ballooning in front of the occupant. At the same time the occupant’s head and upper body is moving with significant force toward the inflated bag. As the occupant’s head strikes the airbag, the bag starts deflating through vent holes in its base. This cushions the decelerating head’s forward movement. The whole process occurs within about 100 milliseconds - about the same time as the blink-of-an-eye.
- In the process of deploying, considerable smoke, dust and noise will be produced and the occupant may be unaware that the bag has deployed. This is normal.
When do they deploy?
For the driver or passenger airbags to deploy in a crash, all the following minimum criteria must be met:
- The vehicle must be travelling at more than about 25km/h.
- The angle of impact is within around thirty degrees either side of the car’s centre line (around 60 degrees in total).
- The deceleration forces produced are at least equal to those produced when the car collides head-on with an immovable barrier at approximately 25km/h.
Note: Front airbags will not be deployed in the event of a side or rear end collision or in a rollover as they would provide no additional protection.
Other types of airbags
- Dual stage airbags are a smarter generation of airbags that optimise the level of airbag deployment to suit the severity of the crash.
- Side and curtain airbags help protect occupants against head, neck and thorax injuries during side impacts and rollovers. Knee bags protect lower limbs from injuries caused by impact with dash panels.
Airbags and bull bars
Inappropriately designed bull bars may interfere with the airbag system’s ability to correctly deploy the bag. Only bull bars that are certified as not affecting crash performance can legally be fitted to later vehicles.
Other airbag Issues
- Front airbags are designed to provide protection for persons of adult proportions. Children, due to their smaller size, are at risk of injury from a deploying airbag. Therefore, children should not occupy the front seat when a passenger airbag is installed.
- Accessories that may restrict the deployment of the airbag or become a missile if contacted by a deploying airbag must not be fitted. Where a passenger airbag is fitted, this includes dash mats, drink, or phone holders, etc. In the case of seat mounted side airbags, seat covers must be checked for compatibility, ask the carmaker.
- Airbag systems normally incorporate a dash warning lamp. If the lamp fails to extinguish soon after start-up or comes on while driving, consult your owner’s handbook, and take the vehicle to a dealer promptly, for checking. The system has detected a fault.
- Unless certain precautions are followed, airbags can be triggered inadvertently during certain repair procedures, especially electrical work. Serious injury can result, so leave repairs to qualified tradespersons.
- Airbags deploy with explosive force and are far from being the big fluffy pillows some people might imagine. Minor injuries and skin abrasions from contact with the bag are common.
- A few vehicle makers specify a life span for airbag components. This typically means that the airbag light comes on and components will need to be replaced before it will go out.
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