A possibility? Yes.

A high possibility on a used car until normal heat and driving vibration?
Not very high - compared to other much more likely auto accidents while driving. From other drivers, from yourself as a driver while distracted by GPS, radio, passengers, text messages, phone etc.

Those airbags are many more orders of magnitude likely to save you from death or serious injury than they are of causing you injury.

Without an ignitor, no.

http://www.caranddriver.com/features/the-physics-o...

Manufacturers use various chemical mixtures to fill the airbags. The solid chemical mix is held in what is basically a small tray. When the mechanism is triggered, an electric charge heats up a small filament to ignite the chemicals, a rapid reaction produces a lot of nitrogen gas.

It is not good practice to be working on the vehicle while in front of the airbag.

A top executive says Takata Corp. is encouraging automakers to replace defective air bag inflators with newly designed ones from the company, or with those made by competitors that don't include a volatile chemical.

The defect is linked to at least six deaths and more than 100 injuries.

The company has declared 33.8 million air bags defective in an agreement with U.S. regulators.

Takata uses the chemical, ammonium nitrate, to inflate the air bags. It can explode with too much force, blowing apart a metal inflator and sending shrapnel into the passenger compartment.

In replacing many faulty air bags, Takata is looking to make air bag inflators with a new design that use ammonium nitrate, or to use inflators made by rival suppliers which don't use the chemical, Kennedy said.

Already, half the replacements that Takata shipped to automakers last month had inflators made by its competitors, Kennedy said. By year's end, he said, that is expected to reach about 70 percent.

The Takata air bag problems began surfacing about a decade ago.

Although the National Highway Traffic Safety Administration and the auto industry are still trying to determine exactly what is causing Takata's inflators to explode, the agency said last week it decided the recall action needed to be taken immediately to protect the public.

Kennedy said there have been fewer than nine failures causing air bag ruptures in the U.S. out of every 100,000 air bag deployments. Most of them occurred in parts of the country with high heat and humidity, he said.