Airbags are proliferating - and we're not talking about tyre-kicking customers and car dealers. They abound in new cars these days.
Every new Peugeot 407 packs in seven airbags waiting to save drivers and front passengers in a crash. The options list brings it to nine if side airbags for those in the back are included.
But, given that they are such a recent addition to cars, little attention has been paid to the sort of lifespan we can expect from such all-important devices. When should you change your airbags?
Today, new cars come with at least front airbags as standard, and many also have side and head airbags or side curtains for those in the front. Steering column/knee airbags as well as side-airbags for those in the back are still relatively new.
Airbags were developed 20 years ago because Americans refused to wear seat belts even though lots of them were dying in crashes, according to GP, a US medical magazine.
But, once a car has left the dealership, the airbags' future seems to depend on several things.
Airbags fire if sensors detect a certain type of accident. They can distinguish a relatively trivial bumper-to-bumper tip from a more serious bang where tiny amounts of explosives or pyrotechnics in the airbag module ignite and trigger a harmless gas. This inflates the airbag and drives it through its cover to cushion the person twice as fast as the blinking of an eye.
In newer cars, seat-belts also use pyrotechnics to restrain passengers. Before 1998, the seatbelt tautness was controlled where the belt was fastened, but nowadays the chemistry is built into the actual seat belt reel, explains Peugeot's Emma Toner.
As these innovations are still relatively young, it's somewhat unclear if they deteriorate with time. "When initially designed, nobody knew, so airbag manufacturers limited liability to 10 years and car companies did the same," says Mats Oldman of Autoliv, a Swedish company and one of the world's major suppliers of airbags. "That's why some cars still have airbags giving expiry dates."
Oldman says that, in reality, airbags probably last as long as the vehicle itself, unless the explosive powder becomes moist. This is very unlikely and probably only a risk in areas prone to high humidity or torrential rain.
But, says Tom O'Connor of VW, the "lifetime guarantee" generally refers only to airbags fitted in the controlled environment when the car is being built and not necessarily for those installed afterwards. It's down to where the bag was stored and how it was handled.
Peugeot says that, up to a couple of months ago, it recommended that the pyrotechnics in belts and airbags be replaced after 10 years but has now increased it to 15 years. This is probably just as well, as replacing airbags which deployed in an accident is a big and sometimes costly job.
Regulations stipulate that airbags can be shipped only under specific conditions which add to costs, says Oldman. The pyrotechnics are supplied to airbag makers by a French munitions company and the main US rocket fuel producer.
If the curtain airbags have deployed, the side of the car must be taken off to replace them and, if the front airbags fire, the dashboard and control module must be removed, according to Toner.
But, whatever the costs, there's no doubt that airbags save lives, although a small number of drivers and passengers, especially in the US, have been fatally injured when they deployed. This was mainly because they were sitting too close - at 10 inches or less - to the airbag cover.
A seat-belt is vital, says Oldman - it's the primary restraint for the body when flung forward. "Airbags are supplementary restraints for use with seat belts. They come out with the force of one tonne and, without the belt, occupants are hurled forward in panic breaking."
Rear-facing child seats should never be placed on a seat where an airbag is provided, adds O'Connor of VW. Many cars have a switch to turn off the passenger airbag if the driver wishes to have the restraint in the front rather than in the much safer back seat, which is the best place for smaller children also. For this reason rear-side airbags such as those in the new 407 deploy vertically, according to Toner.
Oldman says the trend is towards more airbags, a factor in helping cars reach the top five-star rating for occupant protection in the EuroNCAP safety tests.
The next big step is "smart" airbags which are more adaptive to crash violence and occupant size. They use cameras and other systems to detect occupant's size and position and then signal to the airbag unit to control or automatically stop deployment.
Like all ongoing developments, perfection may take time. In the US, where manufacturers are under pressure to install smart airbags in the next year, one motorist told regulators the passenger-side airbag of his 2004 luxury car stays off unless his six-stone wife has a 10-pound bag of potatoes on her lap. A solution to a different problem, perhaps.