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Getting to know cars – Airbags

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Written by Bankole Singerr

Make yourself comfortable as I break down to you an especially common safety feature in modern automobiles.
I advise you get a cold glass of orange juice (but unless you are a ‘wanna-be-British’ bloke or lady, a cup of tea will do the trick) as you read this dialogue. Enjoy!

Today, we are dissecting the Airbag system. First, let’s start by defining and explaining what an airbag is. Well, it’s an inflatable bag installed by car manufacturers in cars or/and in specific trims of these cars in particular contact points and are activated on accident impact. They burst out of where they have been installed to cushion the driver and passengers in a vehicle and shield them from as much contact with the vehicle frame as possible . Installation points can be identified with little signs around the interior of the car reading ‘SRS Airbag’, ‘SIR Airbag’ or just ‘Airbag’ (And of course, ‘SRS’ means Supplementary Restraint System. ‘SIR’ means Supplementary Inflatable Restraint).

The floor is now open to ask your questions.

Question 1: How fast do you have to be going before the airbag(s) go off in a crash?

Answer: It’s not a matter of how fast you are going. Like all crashes, it’s about how quickly you come to a halt. An absurd example: Driving at 60kmph into a giant bread loaf is not the same as driving at 60kmph into Olumo Rock.

Question 2: But how does the airbag know what I’ve crashed into?

Answer: Like a Thermos flask, it doesn’t know whether or not the water in it is cold or hot. The sensors that set them off measure deceleration- or acceleration (if it’s a side airbag). Imagine you’re driving along with an apple on your lap. When you hit the giant bread loaf, it won’t shoot into the foot well (or in lame mans English, pedal area) as rapidly as it would if you’d hit Olumo Rock.

Question 3: But airbags don’t use apples, I’m guessing?

Answer: No, early airbags used sprung weights in tubes. Later ones used mercury switches. These days, there are multiple sensors linked to baffling computer algorithms (precise step by step calculations) that can decide how forcibly to deploy the bag, and which bags to deploy if there are lots of them.

Question 4: Well, I was going to say. Driving head on into Olumo Rock, as your example goes, is not the same as being driven into by Olumo rock (if she has wheels and an engine) is it?

Answer: Exactly! The system works out what has happened and sets off the appropriate airbag at the appropriate rate. Some curtain airbags are set off when sensors detect that the car is rolling over, even if it hasn’t hit any pre-historic volcanic sediment whatsoever.

Question 5: It doesn’t have very long to work this out, does it?

Answer: As far as human perception is concerned, it happens instantly. The typical reaction time is around 20 milliseconds; typical time to inflate the driver’s airbag is 60-80 milliseconds. Remember a millisecond is a thousandth of a second. That’s about the time it takes you to blink your eye when something touches it… Hmm… That’s bloody quick. And it’s because crashes don’t last very long.

Question 6: How can it inflate that quickly?

Answer: There is a solid propellant behind the bag, and when triggered, it explodes and changes to a gas, typically nitrogen. It’s sort of like a shotgun cartridge, but without the lead balls. So-called dual stage airbags inflate in two bursts.

Question 7: Is it loud?

Answer: Yes. But crashes are rearly quiet if I might say. You probably wouldn’t differentiate the sound of the airbags from the crash. You’ll be too concerned about whether or not you are going to heaven or hell…

Question 8: So, one minute you’re driving along then the next instant you’re resting on a giant balloon right?

Answer: Not a very good balloon. In the case of a front airbag, it starts to go down as soon as it’s fully inflated. It has vents in it to make this happen. Otherwise, it would be rock solid, and you might as well bang your head on Olumo Rock. But side and curtain bags will stay up a bit longer.

Question 9: And how big is this airbag?
… Your questions are getting too many. I’ll take just one more after this…

Answer: It depends where it is. The passenger bag is generally bigger than the drivers, because it’s further away. American airbags are often bigger than Europe ones, because they are better at wearing seatbelts. Mercedes is working on a ‘size adaptive’ airbag, which will ‘know’ the size of the occupant and seat position, and inflate the bag accordingly (pioneering new technology just the way she has for over a century).

Question 9: Can the airbag itself cause injuries?

Answer: There have been cases of injury and death attributed to airbags, but it’s much rarer with the modern systems. Thanks. Our time is up. That’s all we can take today… enjoy the rest of your day.

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