Bang! We think of explosions as terrible, dangerous things—but that's not always the case. Every day, explosions are helping to save people's lives. If you're unlucky enough to be involved in a car accident, a carefully controlled explosion will (hopefully) fire an airbag out from the dashboard, cushioning the impact and helping to reduce the damage to your body. Airbags are very simple but also amazingly clever, because they have to open up at over 300 km/h (200mph)—faster than a car can crash! Let's take a closer look at how they work.
An airbag is more correctly known as a supplementary restraint system (SRS) or supplementary inflatable restraint (SIR). The word "supplementary" here means that the airbag is designed to help the seatbelts protect you rather than replace them (relying on an airbag to protect you without fastening your seatbelt is extremely dangerous).
The basic idea is that the airbag inflates as soon as the car starts to slow down in an accident and deflates as your head presses against it. That's important: if the bag didn't deflate, your head would just bounce back off it and you'd be no better off.
How airbags work
When a car hits something, it starts to decelerate (lose speed) very rapidly. An accelerometer (electronic chip that measures acceleration or force) detects the change of speed. If the deceleration is great enough, the accelerometer triggers the airbag circuit. Normal braking doesn't generate enough force to do this.
The airbag circuit passes an electric current through a heating element (a bit like one of the wires in a toaster).
The heating element ignites a chemical explosive. Older airbags used sodium azide as their explosive; newer ones use different chemicals.
As the explosive burns, it generates a massive amount of harmless gas (typically either nitrogen or argon) that floods into a nylon bag packed behind the steering wheel. As the bag expands, it blows the plastic cover off the steering wheel and inflates in front of the driver. The bag is coated with a chalky substance such as talcum powder to help it unwrap smoothly.
The driver (moving forward because of the impact) pushes against the bag. This makes the bag deflate as the gas it contains escapes through small holes around its edges. By the time the car stops, the bag should have completely deflated.
Over the years, protective systems have been improved and extended also. After driver and front passenger airbags, Mercedes-Benz developed sidebags and headbags for protection during lateral collisions – with great success. According to the findings of accident researchers, the probability of serious or fatal injury in the event of a lateral collision in a vehicle equipped with headbags is reduced by more than half. The proportion of seriously and fatally injured occupants in lateral collisions fell significantly in the cases examined.
Protective systems are becoming more and more intelligent. Belt tensioners, for instance, improve the protective effect of seatbelts. Multi-stage airbags respond according to accident severity. All in all, the control systems for these onboard safety features now have the processing power of the ‘supercomputers’ used in space exploration 25 years ago.
Although perhaps not as influential as the seatbelt, the airbag’s contribution to vehicle safety is indeed significant – and when combined with a safety harness unparalleled in terms of saving lives and reducing injury.
All safety experts agree that the airbag can never be a substitute for seatbelts. It is only in conjunction with a seatbelt that it becomes an optimally coordinated system that demonstrably makes a major contribution to the prevention of severe or fatal injuries to the occupants during serious accidents.