[alfa] RE:Airbag squibs

["John Fielding" <johnf@xxxxxxxxxxxxxxx>]

Hi All,

In case you did not realise,  squib is a name given to pyrotechnic explosives (aka
detonators).  Normally activated by an electric current.  Squibs are widely used for
detonating explosives and fireworks.  Some years ago I was involved with the design of an
automatic firework display circuit.  We had several hundred squibs controlled by a
computer to set off the fireworks in the correct sequence.  A typical squib can be fired
with a small penlight torch battery, about 100mA is all it takes to detonate one.  So be
very careful when playing with the wiring on an airbag fitted vehicle!

Squibs have a limited life.  Typically the squib and gas canister should be replaced every
5 years or so.  The same goes for the airbag elastic element.  On the Audis the service
interval here is 4 years.  High ambient temperatures cause the airbag to degrade quicker,
hence the recommended service period here is shorter than some other countries with more
temperate climates.  The resale price of Audi A4s and other similar veicles drops like a
stone once they exceed about 3 years because of the high cost of replacing the airbags.

An amusing story was told to me by an auto-electrician who used to work for the local
VW/Audi dealer.  A female borrowed her husbands new Audi company car to go
shopping whilst he was away overseas on business.  Never having driven the Audi
before she misjudged the entry speed into their driveway, stood hard on the brakes,
and the car slid off the gravel driveway onto the lawn.  As the lawn was slightly
downhill the car, with all the wheels locked up, gently slid until it contacted a stone
wall with its front bumper. There is an impact detector behind the plastic front bumper
set to trigger at about 5km/h or higher. The impact speed was about walking pace.
All the airbags were deployed. When her husband arrived back she confessed to
her mishap. The husband said not to worry he would take it into the agents and get
it fixed. There was no other damage to the car. When he got the bill for replacing all the
airbags he almost had a heart attack!  The cost was about 10% of the purchase
price of the car.

John
Durban
South Africa
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