This week for a technical article I am going to talk about a passive safety device that is now on all cars – the airbag – and like diesel has now become enemy #1 for the media who love to write negative stories. With respect to airbags, one company, Takata, who had manufacturing issues that affected millions of units has caused all the negative press. So bad was the problem that the company was financially stricken to the point of being acquired and absorbed into another company.
The first airbags were designed by engineers in the mid 1950s although they were never fitted to any cars. The first one designed by John Hetrick was covered by a patent and when that ran out, other engineers started to look at combining the bag with a crash sensor. Several companies worked with the Big 3 in the US (General Motors, Ford and Chrysler) to get an airbag into a car as a prototype.
It was during the late 1960s and early 1970s that the manufacturers tested fleets of cars with them fitted although early versions were treated as a replacement for seat belts rather than the current and more sensible method of using them as a supplement to the belts.
As you can imagine, airbags were first released to the market on high end marques like Mercedes-Benz and Porsche with other companies adding them to their luxury ranges first. As the costs reduced and Government regulations changed, airbags found their way down to even the cheapest models which was important for road safety. It did take nearly 20 years to filter down through the market segments!
The first airbags were fitted inside the steering wheel as well as passenger ones fitted to the dashboard and even knee airbags to protect the drivers legs. Nowadays, airbags can be fitted everywhere inside a car – there are side bags, air curtains and even rear curtains fitted to cars on the market. Each one is designed to protect the occupants from an impact from a particular direction.
Ford were the first to announce that they had fitted an airbag to a seat belt to help with the chest protection of occupants. Lexus and Mercedes-Benz quickly followed and this is now common on cars defined as luxury with some medium priced vehicles also having them fitted as standard now.
Well, how do airbags work? As described at the beginning of this article, there are crash sensors fitted across a vehicle that trigger the bag. These sensors aren’t just impact sensors – that would be too late in the event – they include sensors for speed, pressure, gyroscopes, accelerometers, decelerometers and seat occupancy sensors. All these send inputs to a black box that assesses what is going on and then when conditions are right, the control unit ignites a gas based propellant that fills the nylon bag – nylon is used as it is a strong material that is easily compressed into a small space.
Different markets have different regulations for the power of the ignited propellant and it is possible to receive serious injuries from an airbag if a seat belt is not worn at the same time. In fact in the US, when airbags were first fitted, the manufacturers also fitted a switch so that the driver could switch them off! The reality is that the occupants may suffer some form of injury from an airbag deploying, however this is offset by the fact that the bags save lives in some situations. Clearly if you are involved in an accident with a very solid object then you will have injuries, but for many different directional impacts, a set of bags may reduce the severity or number of those injuries.
Airbags have even found their way to motorcycles and motorcycle jackets where the bag helps reduce the severity of the impact when a bike is involved in an accident. In this design, the rider’s jacket is clipped to the motorcycle with a cord. On having a rapid unscheduled departure from the bike, the cord triggers a gas canister to inflate the neck and spinal area of the jacket, thus providing better protection on impact.
The current issues surrounding airbags was due to a manufacturing issue with Takata-made bags that had several complications. The first factor is that Takata used Ammonium Nitrate for the propellant – not used by their competitors because they found it to be unstable! Other manufacturers used a Tetrazole based propellant or Sodium Azide to trigger the inflation. Cost was a factor in Takata moving to Ammonium Nitrate as was concerns about supply of the Tetrazole propellant. Takata had also used the Sodium Azide propellant, however that product had issues around toxic fumes!
As an air bag gets older, the propellant chemicals degrade and become more unstable. Adding to this was a problem with the construction where a small amount of humidity had been trapped in the unit, also causing further instability of the chemicals. This particular issue was isolated to one factory in Mexico. All this resulted in airbags exploding with a higher force than intended and in some cases propelled the casing into the occupants causing serious injury or death.
By the time the National Highway Traffic Safety Administration (NHTSA) in the US triggered one of the biggest recalls in history, several people had died from injuries sustained from the airbags not the accident itself and Takata was supplying a large portion of the car industry – hence the widespread recall!
The issue was compounded by owners of cars not responding to the manufacturer’s request to get the airbags replaced and if they did, the service centres often didn’t have any replacements as there was a shortage of availability! To make the situation even worse, was the discovery that many of the newly manufactured airbags were also faulty.
I believe the future for airbags is still good, engineers are using more sensors to determine the size of the occupant as well as the direction of impact so that a more progressive ignition of the propellant can be made, thus making the deployment safer for the people inside the vehicle. In addition, the boffins are researching better propellants and with new materials and designs to reduce the possibility of the airbag causing the most serious injuries, we should see a reduction in fatalities.
Fundamentally though, the car owner and driver has a big part to play in the safety of the vehicle. Some lawsuits regarding the airbag sourced injuries have come from drivers who disobeyed road rules or even had cups of coffee in their hand at the point of impact! An airbag can only be a small part of a full safety system – it cannot be considered as the sole safety unit.