Expert advice: all about the airbags in your car

One high tech feature of all modern cars that I never hope you see is the airbag. These are designed to inflate milliseconds after an impact and work with the seatbelts to prevent you hitting any hard surfaces in the car.

They can go wrong but thankfully it’s not something we see very often. But it’s still worth knowing a bit about airbags.

Which cars have airbags?

Airbags have been standard on the majority of cars since the late 1990s. Independent car safety assessor Euro NCAP will slate a car’s safety performance if it doesn’t have airbags these days. And even Britain’s cheapest new car, the £6995 Dacia Sandero, has driver, passenger and front side airbags.

Generally, if a car is less than 20 years old, it’s likely to have airbags fitted. And the more expensive the car, the more airbags it’ll have.

How do airbags work?

Imagine a nylon bag that inflates in fractions of a second and you’ve pretty much got an airbag. Rather like a parachute, they’re folded up in a small space, for example the centre of the steering wheel or behind the dashboard above the glove box.

Airbags have their own control unit. This can detect an accident because its sensors can tell from the sudden deceleration. When airbags are told to deploy, chemicals are combined. This forces a reaction which creates a propellant usually generating nitrogen. All this happens in the blink of an eye, usually between 25 and 40 milliseconds.

Airbags have vents behind them that mean as soon as they inflate the gas starts to pour out of them. This makes them softer and more forgiving when the car occupant hits them.

Although initially airbags were invented to replace the seatbelt, research has proved it’s best if the two work together. This is known in the trade as a Supplementary Restraint System. That’s why older cars feature the letters SRS before the word ‘airbag’.

Do airbags ever go wrong?

There are tales of airbags going off spontaneously but thankfully they are few and far between. A more serious problem was a recent recall for cars fitted with airbag systems from Japanese company Takata. That could be pretty much any model from the Japanese manufacturers but also includes cars from the Volkswagen Group and Jaguar Land Rover among others.

It was found that in some cases, when the airbag went off, the metal casing surrounding the propellant was being fired at 100mph-plus into the cabin. Check if your car was subject to a recall for its airbag on this government website.

How long do airbags last?

Back in the day, some car makers said airbags would need to be replaced after about 10 to 15 years. However, replacing airbags is an expensive business so that has been revised. The motor industry now agrees that time has proved airbags should last the life of the vehicle.

No part of the MOT examines airbags. But if the airbag warning light stays on, a car will fail its MOT. And in an older car, the high cost of replacing an airbag invariably means the car will have to be scrapped.

What if the airbag light comes on?

If the airbag warning light does come on, it’s important to get it checked out by a professional. They’ll be able to plug into your car’s diagnostic system and find out what’s really going on.

And if you do have a crash

Although you’ll probably be too busy processing what’s happening to brace yourself, when an airbag goes off in the confined space of a car interior it’s very noisy indeed. And the bag fires out at terrific speed.

Safety organisations advise drivers that having their arms in the ten to two or quarter to three position is best. If your arm is the other side of the steering wheel, the force of the airbag could break the limb.

You should not use a rear-facing child seat with an airbag as they can injure the child. That’s why there are stickers warning you to turn off the passenger airbag if you use such a seat.

When the airbag does fire, the cabin is likely to appear to fill with smoke. This is talcum powder or flour used to prevent the airbag sticking to itself while it’s stored away. But the mess it makes, plus the requirement to have a new airbag or bags fitted on top of any other damage, is likely to be pricey enough to make a repair uneconomically viable. Here’s hoping it never happens.

Nick Reid is head of automotive technology for Green Flag and is a fellow of the Institute of the Motor Industry