Designed to work in combination with seat belts, airbags are deployed when a car comes to a sudden halt, usually as the result of a collision. Occupants and other items in a car are subject to momentum, which just means that they continue to travel forwards when the car is decelerating. Under heavy braking, items in a car, such as handbags and road maps, can be thrown forwards. In severe cases, this could even mean that the driver and passenger will be thrown toward the windscreen during a road accident, potentially launching them through the glass. Seat belts can do a good job of preventing this, but impact research has shown that people still get injured by smashing into the internal parts of a car even when they have a seat belt on. Drivers can be at particular risk of injury since they have the steering column in front of their bodies. The earliest airbags were therefore developed to prevent such injuries, particularly focusing on protecting the driver from their steering wheel.
The Technology Used in Airbags
Airbags are more usually referred to in the motor industry as a supplementary restraint system, which means that they are only good as supplements to seat belts rather than replacements. Therefore, the technology that has been developed for them has always gone hand-in-hand with the technological advances put forward in seat belts. That said, modern airbags are surprisingly high-tech.
The central part of an airbag that decides whether or not to deploy is a device called an accelerometer. This is basically a chip that measures the forces exerted on it by detecting changes in speed. Under normal braking, it does not deploy, but if braking is hard enough - or if the car comes to a halt from striking something - then it will.
Deploying the Airbag
Detecting excessive braking or a collision is one thing, but for an airbag to be of any use, it must deploy. Should the accelerometer detect a strong enough force, it will trigger the airbag circuit. Almost instantly, the airbag circuit heats up from the electrical current now being passed through it. The heating up of the circuit will ignite a chemical explosive, such as sodium azide, in a fraction of a second. As whichever explosive that is used burns, it generates a large amount of gas that inflates the bag. Most airbag designers use nitrogen or argon to fill their bags. These chemicals are harmless to people due to the quantities involved.
Protecting the Occupant
Airbags are usually hidden within the dashboard or steering wheel of a car. However, the force generated by the gas inflating the bag is sufficiently strong to make a cover flip out of the way. Typically, a driver's airbag is set into the steering wheel and its cover simply gets shoved aside when the bag is deployed. To help the bag unfold correctly, it is sometimes coated in powder. As the driver or passenger comes into contact with the bag, it protects them from harder surfaces. Bouncing off the bag is avoided by small holes in it which allow the gas to escape, cushioning the blow. Once deployed, most people see the bags in a deflated state before they realise what has even happened.
Other Types of Airbags
Most airbags are fitted in cars to protect people from front-facing impacts. However, car makers have gone on to develop all sorts of other airbags. For instance, one type can deploy on a side impact. Curtain airbags came into use in the late 1990s and don't just protect occupants from side collisions, but can also shelter them from shards of flying glass and from the vehicle itself if it rolls over. Knee airbags were invented soon afterwards and are designed to protect front-seat passengers from hurting themselves on the glove compartment, a common problem before the system's deployment.
Airbags are not just for cars, either. They are also fitted in vans and trucks. In 2006, Honda introduced a world's first for airbags when they fitted one to their Gold Wing motorbike. They are now widely used by professional racing motorcyclists.
Children and Airbags
Because airbags are designed for adults in cars, some child seats are not suitable to be used where they are fitted. This is usually overcome by fitting a child seat in the rear, but where this is not possible the child seat usually needs to be rear-facing. Alternatively, the airbag should be simply turned off.