Air Bag Not Deploy problems of the 2003 SAAB 9-3

I was driving my 2003 SAAB 9-3 se convertible to the nearby publix supermarket. The car has never been in an accident or hit. I parked it in the lot with the top down and went into the store for approximately 10 minutes. It was a warm dry day in florida about 85 degrees. I came out and put the key in the ignition and turned it to start the car, and the passenger side airbag exploded for no known reason. I called gm, they took the car to a gm facility and inspected it, and then came back a week later and said the unexplained deployment of the airbag was not a manufacturers defect and they would not repair it. I find that difficult to believe. The airbag should not deploy arbitrarily when the ignition key is turned.

Airbags did not deploy in a 30-35mph frontal collision with an oncoming vehicle. Seatbelt restraint injured both passengers, but none of the airbags deployed.