airbags

[jenko]

whats the lowest impact speed until the airbags blow ???

 

[Craig]

depends some have gone off a 5mph

 

[GordonD]

There is a concept in crash engineering called "aggressiveness". Because the severity of crashes goes up with the square of the speed they occur at crash structures and devices have to be designed for a speed at which they work best. If you design a crush structure to be stiff enough to collapse in 0.5 seconds to save a life in a 40 mph crash the much lower forces in a 20 mph crash might mean it doesn't crush at all and the vehicle occupant is injured, and the much higher forces in a 60 mph crash might mean it it crushes so fast it doesn't do any good. Its the same with airbags. If you design them to expand fast enough to work just right in a 40 mph crash they won't expand fast enough to do any good in a 60 mph crash, and they'll be too violent in a 20 mph crash and may cause more injuries than they prevent in crashes that occur at low speeds. In fact the studies done show they do. So at various times it has been suggested that some minimum speed be dictated below which they don't activate. But there's a complication that vehicle occupants may or may not be wearing seatbelts - non-seatbelt wearing occupants need more aggressive protection - and in some countries seat belt use is compulsory whereas in others it isn't. There are also "smart" airbag systems that look at the speed and look at a sensor that detects the weight of the occupant of the seat to decide whether the bag will be activated more or less aggressively.

If the airbag system in a car is labelled something like "supplementary restraint system", ie it is designed for use in conjunction with seatbelts, it probably has a minimum activation speed of 24 km/h (15 mph). If it isn't labelled like that its considered the "primary" restraint system, and it activates at anything over a certain impact force as detected by a number of sensors around the car. In practice its unusual to reach that force in a very low speed impact. But it does occur in some circumstances.

 

[GordonD]

If the airbag system in a car is labelled something like "supplementary restraint system", ie it is designed for use in conjunction with seatbelts, it probably has a minimum activation speed of 24 km/h (15 mph).

I note that the cover on the steering wheel air bag in the Clio is labelled "SRP" on it, which indicates its only a "supplementary" system, and it may well have a minimum speed at which it can activate.