The purpose of an airbag is to reduce injury by either cushioning the occupants contact with the interior of the vehicle or preventing contact completely.
- An airbag is a large nylon bag which inflates and deflates very rapidly in the event of a severe 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.
- Other airbags could also be found in the lower dash, seats, seatbelts, roof pillars and roof structures.
- Some motorcycles also have frontal airbags.
How airbags work
- 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 / dash / pillar / seat etc, as it emerges.
- In the case of a front airbag, as the occupant’s head and upper body moves forward and strikes the inflated bag, the bag starts deflating through vent holes in its base to cushion the decelerating head’s forward movement.
- The whole process of inflating and deflating occurs within about 100 milliseconds - about the same time as the blink-of-an-eye. The process is so fast that the occupant is often unaware that the airbag has deployed.
- Side and curtain airbags are sometimes slightly slower to deflate as the types of crash they are designed to protect against are different to frontal impacts.
- In the process of deploying, considerable smoke, dust and noise is produced. 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.
- Knee bags are fitted to some cars to protect lower limbs from injuries caused by impact with dash panels.
- Some manufacturers provide seatbelt airbags to reduce seatbelt induced injuries
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.
Airbags and children
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.
Other airbag Issues
- 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, Sat navs etc.
- Where seat mounted side airbags, seat covers must be airbag compatible. Ask the car or seat cover maker.
- Airbag systems normally incorporate a dash warning lamp. If it fails to extinguish soon after start-up, or comes on while driving, it is indicating a fault that need to be promptly checked by a dealer.
- Airbags can be triggered inadvertently during certain repair procedures so special precautions need to be applied. 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.
- Airbags are designed to operate in conjunction with the car's seatbelts. Failure to wear a seatbelt may actually result in increased injuries.
- 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.
There is currently a mandatory recall of certain Takata brand airbags. These are fitted to many different makes and models and are responsible for approximately 24 deaths and hundreds of injuries throughout the world. For further information see
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