We’ve had a few questions about airbags not going off. It’s worth repeating that airbags aren’t designed to inflate in every type of crash.
How do airbags go off?
Airbags deploy, another word for going off, when they sense the car is having an accident. The units essentially have three parts. The impact sensor, the bag and the inflation charge.
When you have a crash, the sensors detect an accident is happening because they can tell from the rapid deceleration. Loosely speaking, they tell the car’s computer about this which then instructs the inflation charge to go off. The bag fills with gas and inflates before instantly deflating.
This entire process takes milliseconds. It’s the inflation-deflation process that gives the airbag its cushioning ability.
What happens when airbags deploy?
Airbags are designed as a supplementary restraint system – hence the SRS Airbag on many of them. They are supposed to work alongside the seatbelts that we all have to wear by law.
With airbags, it’s important to realise that once they’ve gone off, you’ll probably be in shock from the loud bang of it inflating, you may well have sore forearms from the friction of the bag exploding against them, and the cabin will be full of dust. This dust is harmless, it’s the powder they wrap the bags in to prevent them sticking when they’re folded up in their container.
Cars have multiple airbags now. Not all of them always go off
Why they may not go off in a rear-end shunt?
If you rear-end someone, although it may feel dramatic, the impact may not actually be that great. For a start the vehicle you hit will probably be moving. And the impact will move that vehicle away from the car that’s run into it faster; it’s not like hitting a stationary barrier.
On top of that, your car might still be driveable. And you might have to avoid other cars to prevent further injury. What the car manufacturer doesn’t want is for the airbag to go off and cause another accident. This might be because the driver’s shocked or perhaps can’t see where they’re going.
The speed differential may not have been that great
Airbags may not deploy at less than 15mph because the car maker may believe that seatbelts will be sufficient to protect the occupants. Equally, if the speed differential at the point of impact is quite low, the computer may not tell the airbags to go off.
Rear-ending another car may mean that on impact, the speeds actually aren’t that different.
It does depend on the car
Of course the above is, to a degree, supposition. We haven’t seen the car and don’t know how old it was or the precise circumstances of the crash.
There may be a fault with the car’s airbag. Although this is unlikely, there have been instances where people have bought used cars without knowing that the car has been involved in an accident beforehand and the airbags haven’t been replaced or have been exchanged for defective items.
If the reader is concerned that the airbag didn’t deploy and their daughter suffered injury because of it, we’d advise they contact the car manufacturer.
I’ve been writing about cars and motoring for more than 25 years. My career started on a long-departed classic car weekly magazine called AutoClassic. I’ve since pitched up at Autosport, Auto Express, the News of the World, Sunday Times and most recently the Daily Telegraph. When I’m not writing about cars and motoring, I’m probably doing some kind of sport or working in my garden.
