Car components : Air bag

What is an airbag?

Airbags protect vehicle occupants from head injury in a collision.

• Most cars now have a driver's airbag fitted in the steering wheel and many have passenger airbags in the dashboard. This type of airbag is designed to protect the vehicle occupants in a front-end collision.
• Side curtain airbags provide protection in side impact and rollover crashes.
• Airbags inflate very quickly in a crash. They are designed to work together with the seat belt but do not eliminate the need for a seat belt (the SRS in "SRS Air Bag" stands for Supplementary Restraint System).
• The inflated airbag cushions the occupant and prevents them hitting the dash, steering wheel, windscreen or side of the cabin with excessive force and so reduce injury.
• A typical airbag for front crash protection starts to inflate within about 20 milliseconds of the start of the crash and is fully inflated 45 milliseconds later. The occupant is thrown forward into the airbag at about this time and starts to sink deeply into the airbag. After about one-tenth of a second the airbag begins to deflate, having served its purpose.
• In a side impact the inflation time is less than 10 milliseconds.
• The bag, made of nylon material, is stored in the steering wheel or the dashboard under a cover and inflates and deflates rapidly during specific types of collision.
• Most airbags are electronically controlled and include a light on the instrument panel to indicate a fault in the system. When the ignition is turned on the light comes on for a number of seconds, during which time a self-diagnosis is carried out. If all components are operating to a predetermined standard the light will extinguish. The light should only come on when driving if there is a problem with the system.
• If your airbag light comes on while driving, take the vehicle to a specialist for diagnosis.
• Airbags can cause serious and sometimes fatal injury if deployed while being repaired.
• Have a qualified technician carry out any work to the control system inside the vehicle.
• The airbag system should always be deactivated before attempting such repairs.
  
  
  Airbag safety

  There is a grave risk of injury if the driver or passenger is seated too close to the airbag.

  • It is recommended that there is a gap of at least 25cm between the occupant's chest and the airbag.
  • It is important to have the seat adjusted correctly.
  • Rearward facing child seats should not be fitted in the front of a vehicle with a passenger airbag.
  • If it is necessary to carry children in the front passenger seat, ensure that the child is adequately restrained, facing forward and that the seat is as far back as possible.
  • It is always extremely dangerous to carry a child on your knee in the front passenger seat. If a passenger airbag is fitted the force of the deployment can only add to the serious injury the child will suffer in a crash.
  • Never drive with your hands on the centre of the steering wheel if an airbag is fitted. Serious injury can be caused to the hands if the bag is deployed.
  • Do not attach any items to the airbag cover, notepad holders, magnets and travel clocks can become projectiles when the bag deploys.
  Airbags and bullbars

  All modern cars have crumple zones designed into the chassis, which compress in a crash to absorb some of the impact.

  • Bullbars can alter the way in which the front of the vehicle crumples and can cause the airbag to deploy at the wrong time.
  • Only fit bullbars that are recommended by the vehicle's manufacturer as being safe to use with airbags.
  • Some after-market bullbar manufacturers have designed products that do not effect the airbag system.

Current trends

Many vehicle manufacturers are now fitting side impact airbags as standard.

• Side impact airbags can be fitted in the seat,the door side panel, or in the area above the door.
• Side impact airbags work on the same principle as front airbags but only deploy in a side impact collision.
• Airbags located in the rear of the front seats can provide protection for rear seat passengers.

Some vehicles now have up to eight airbags fitted and all or some will deploy under predetermined circumstances. Intelligent airbag systems control airbag deployment according to the crash characteristics and other factors such as:

• The number and location of occupants.
• Seat position and adjustment.

Airbags and used cars

If you are buying a used car remember that the airbag is considered to be a part of the car and is therefore required to be in working order for the vehicle to be considered road worthy.

An airbag is not an accessory as it is part of the restraint system designed to protect occupants in a crash. In many cases it is required to enable the vehicle to comply with Australian Design Rules and to be approved for sale in Australia. When buying a used car, check the following:

• When the ignition is turned on the airbag light in the instrument panel should stay on for approximately three seconds and then go out. This indicates the system is OK.
• If the airbag light does not come on, there is a fault. Either the warning light has been interfered with or the airbag system is faulty. In either case you should ask the dealer to fix the fault before you purchase the vehicle.
• If the airbag light flashes intermittently there is a fault in the system that requires investigation.
• Disconnection of the airbag is illegal as it is part of the vehicle's original safety equipment. It is an integral part of the restraint system, which includes the seatbelts and the design of the steering column.

How do they work?

The main components of the airbag system are:

• Airbag.
• Inflator.
• Electronic crash sensor module (ECS).

If the vehicle is involved in a severe frontal collision, the ECS determines the rate of deceleration of the vehicle and if satisfied that the airbag needs to be deployed will send an electric signal to the inflator.

• When this signal is received the igniter, which is part of the inflator, ignites a chemical which generates the nitrogen inflator gas.
• This inflates the bag and then dissipates through bleed holes in the bag.
• All this occurs in less than a blink of the eye.
• Some cars have more than one sensor and need at least two of these sensors to detect an impact before the bag is deployed.
• The decision to deploy is determined by both the severity, direction and type of impact. It is possible that the lower end passenger airbag would not deploy in a rollover or impact at low speed.