Airbags are one of the latest in technological advances that have been made with in-car safety products aimed at keeping you alive during a road collision, but what is your perception of all that happens when an airbag is deployed?

Just about everyone at some time must have seen film footage on the television of crash-tests being carried out with vehicles manned by crash test dummies, and will watch bemused as the brightly painted vehicle glides along

in slow-motion and begins to crumple against a large block of concrete. As this happens you see those artificial humanoid forms flop forward, and at the same time, a white coloured balloon like pillow explode from the steering wheel or dashboard.  It seems almost tranquil to see the droid-like figures flop onto them, like a playing child falling face forward onto a feather-filled cushion. How comfortable it looks and how safe it makes you feel when watching it.

Being someone who has had first-hand experience of being saved by an airbag deploying in anger I can tell you that reality is far from the fantasy the televised crash tests will have you dreaming of. The experience is one that is hard to explain well enough to give someone the flavour for it, but to try and help you to understand I will use this analogy.

Did you ever have one of those space-hopper things, as in those big plastic balls inflated with air and with a handle on the top?  You know, the thing that either you or your kids used to bounce around on in the garden?  Now imagine a fit healthy and athletic man holding onto one of those, but instead of it being covered in a shiny, smooth plastic material, think of one that has a jacket of very rough grit sand paper. Still keeping that in mind, think of the athlete swinging the space-hopper with full strength around his head and then slamming it into your face. Now you are getting closer to the reality of being on the receiving end of coming face to face with a vehicle airbag as it deploys in a collision.  What you come out of it with is chemical burns around your eyes and nostrils and a face spattered with gravel-rash.  Nevertheless, I am sure that had I not had the luxury of one of these devices I would have sustained far greater injury.

With my experience behind me I used to give a wry smile to myself, when in my former life as a police roads policing officer, I used to attend a minor road accident and would hear a disgruntled driver saying, “I thought these airbags were supposed to go off in a crash?” If those people had ever had the experience I have of an airbag, they would be very thankful that it hadn’t gone off – certainly not in the case of a crash where the forces involved allowed the vehicle occupants to be left walking around complaining about the state of their car. Thankfully the amount of collision energy that is required to activate the deployment system of a safety airbag has to reach a substantial level before it is deployed, because the intention is that it should only be so deployed in the type of impact that would otherwise leave you dead, or at the very best, critically injured.

When you look at the construction of an airbag, and its mechanism, you will learn that it is activated by an electronic device acting as a switch and which is triggered by a pre-determined rate of deceleration of the vehicle.  If the forces involved reach the required level the switch will complete an electrical circuit, which in turn will trigger an explosive charge that otherwise remains dormant within the airbag stowage compartment.  Yes, that’s right, you and your passenger are sitting there in the car looking at an unexploded bomb, right there in front of you.  Many cars being produced in the 21st Century have multiple airbags, being fitted to B-pillars, seat backs and in various overhead positions within the roof lining.  They can be all around you, and in a big impact, they will probably save your life.

When the explosive charge is detonated the airbag envelope becomes inflated with nitrogen gas which causes to burst from its hiding place and into the appropriate position from where it does its job. The envelope itself, made from a nylon type fabric, actually has vent holes in it, as it is not intended that it should remain inflated once discharged. The idea is that as the human body falls into it, all the gas is expelled from the envelope through the vent holes, which is how it provides the cushion effect.

An airbag can not do its job properly without the assistance of the seat belts, as the two systems are designed to work in harmony with one another.  In the early days of airbags the one big problem was that the safety belt allowed the vehicle occupants to move too far forward, and so causing too great an impact between head and airbag.  What used to happen in this situation was the head of the subject would collide with the airbag before the airbag was fully inflated, so instead of you landing into the airbag, the airbag would come out and attack you.

To overcome this, modern seatbelt systems have a device built into them known as a pre-tensioner and this is connected to the same trigger mechanism that fires the detonator for the airbag.  What these things do is to take in an slack in the seatbelt, pulling it tight into the body of the wearer, and so effectively pinning them to the back of their seat.  This allows the airbag to do its job more effectively and ensured that the head of the vehicle occupant would connect with the airbag at just the right time during the inflation process.

The damaged police vehicle in the photographs is a 1998 Vauxhall Omega traffic patrol car and when it crashed I was in the front passenger seat.  The speed upon impact was 50 miles per hour as it ran into a solid immovable object in the form of a steel structure that was deeply concreted into the ground. When I say it was a solid object, if it had been something that could have been asleep, the 50mph impact would not have even caused it to stir, let alone wake it up!  There was absolutely no give in it whatsoever.

The collision speed was determined, not by way of an estimate, or saying that the car doing 50mph before brakes were applied, but an actual impact speed of 50mph, as mathematically and scientifically proven by accident investigators.

The make of the car, as far as this story is concerned, is not important, as it is the fact that the vehicle was fitted with industry standard airbags and seatbelt pre-tensioners for both driver and front passenger that is the point here, and the fact that both airbags deployed upon impact.

When it happened there was a deafening bang and then everything fell silent.  The first thing I became aware of was the fact that the interior of the car was filled with was appeared to be smoke, but in fact this was a talcum powder type substance, which came from within the stowage compartments of the airbags and is something that is used to protect from dampness.  Nonetheless it is easy to see how this could be confused for smoke, and then the subsequent worry that the car was about to burst into flames.  The first instinct in that situation is to get out, and after quickly checking that both arms and both legs were still attached and working, and that I was not leaking blood from anywhere obvious, I reached for the seatbelt clasp.  Now this is the weird bit, because I couldn’t readily find the seat belt clasp.

I mentioned earlier about pre-tensioners, and how they are activated at the same time as the airbags with the result they take out any slack in the seatbelt, and the fact this car was fitted with them. If you have a fairly modern car the chances will be that it is fitted with seatbelt pre-trensioners. Next time you are in the vehicle, take peek down the side of the seat, the side nearest the middle of the car. IF you can see what appears to be a black gas canister with a yellow label on it, that will be a seat belt pre-tensioner.

What happens when the pre-tensioners are activated is that the part of the seatbelt system, into which you locate the tongue from the actual belt, will move rearward and downward, as that is how it tightens the belt.  The thing is that when you get in and out of these cars as often as I did in the course of my job, and to put on and removed the seatbelt just as many times as that demanded, it was as easy to perform as touching the end of your nose with your eyes closed.  However, imagine trying that one day, when unbeknown to you, someone had moved your nose to another part of your face.  The fact that you have been in a substantial crash, and you found yourself in a cloud-filled car that is extensively damaged, is confusing enough, but when you reach for the button to release your belt, only to find it has been moved, that is really baffling.

At the time of the collision I was wearing a pair of sunglasses, and as the airbag struck my face, the bridge pads of the shades were rammed into my face on either side of the bridge of my nose and then the glasses were pushed upward over my forehead. The glasses flew backwards within the car, and whilst we remember here that everything else is going forward during the impact, they were later found on the rear parcel shelf!  Make no mistake about the power of the airbag, as such is the violence of the explosion that occurs during activation these things are capable of throwing a child from the front seat of the car and into the rear window.

When I got out of the car my face was covered in what is best described as gravel rash and with droplets of blood standing on the surface of my skin.  I had two gouged furrows up my forehead caused by the sunglasses and my eyes, nostrils and lips were stinging from the effect of the chemicals from the airbag detonator.  Sodium Azide (NaN3) and Potassium Nitrate (KNO3) were reacting with the moisture in these areas of my body.  Apart from that I was intact, and the mild discomfort of a stinging face was a small price to pay for still being in one piece, and more importantly, still being alive.

You will note that I have so far not mentioned the driver of the car, and for the purpose of sharing this account with you I shall introduce him now as Dave.  His situation was different, as just before the main impact, and whilst fighting for control of the car, Dave managed to get his right forearm across the centre area of the steering wheel. The driver’s airbag is located in the steering wheel and when this deployed it smashed Dave’s arm into his face, breaking and displacing his nose, but his arm didn’t stop there.  The force of the airbag pushed it over the top of his head, and his seat head restraint, before it ended up behind the middle of his back. You might at first think this should not be a problem, but if you are sitting in a chair whilst reading this page, put the back of your forearm against the bridge of your nose. Now move it upward to the top of your head before trying and get it over the top and down your back. You can’t do it can you? Now imagine what it would be liked for someone or something to force it to do that.

The broken nose was not too much of a problem, as that kind of injury will usually heal well, but the effect of the arm being forced into an unnatural position was something more serious.  The movement pulled Dave’s shoulder out of its socket and tore all his muscles and ligaments to ribbons. That crash happened in 1999, and when I retired from the police service in 2005, Dave was still being treated for that shoulder. The prognosis was that it will never be fully fit again, but in spite of his injury, he too was still able to walk away from the car, and like me, he owes his life to the seatbelt and airbag system fitted to the car.

The photographs may not accurately convey the degree of impact that took place, but if I tell you that the bodywork at the back of the driver’s side headlamp mounting ended up hitting the bulkhead at the rear of the engine bay, and the bulkhead itself moved backwards pushing the dashboard further into the cockpit, you might begin to get some idea of the strength of the impact involved.

There is something that every driver or vehicle passenger needs to consider, as whenever you see the initials SRS written on a vehicle dashboard, piece of internal trim or the steering wheel centre, it means there is an airbag beneath that covering.  The initials SRS stand for Secondary Restraint System, which means the airbags are intended to work with a seat belt and not instead of a seatbelt – the seatbelt being classed as the primary restraint system. If you are a driver who does not wear a safety belt, be warned, as a human body going forward into an airbag bursting from its recess in the dash or the steering wheel will probably cause more injury than it will prevent.  One more thing to consider here too.  If you are like the 98% of drivers who immediately abandon the traditional style of feeding the wheel when steering in favour of the more popular rotational (cross arms) method, just think of what lies beneath your arms as you do this, and then just spare a thought for Dave.