A mitsu Mirage DE 1998 had a front severe impact while park and both air bags deploy without ignition on.As the wiring diagram shows two ignition signal to SRS computer, seems to me not possible to happen a deploy without ignition on.There is a book ( european ) that says that american versions can deploy without ignition on.Any comments will be appreciable.
thanks 

There are two main sensors that must both be 'satisfied' for the airbags to deploy; the impact sensor and the safing sensor. The impact sensor usually is located near the fenders or behind the headlights, and a safing sensor is centrally located inside the car. The safing sensor ensures that airbags do not deploy accidentally. In a collision, the impact and safing sensors must agree that an airbag deployment is necessary. In addition, the sensors won't trigger when the ignition is turned off, so someone bumping your car in a parking lot will not deploy the airbags.

Now, there may be a threshold as to the severity of a stationary impact with the ignition turned off. Meaning, if the front impact is so great, the airbags either deploy as programmed or due to wiring damage, causing the airbags to deploy. There have been cases where insulation on the SRS wiring gets stripped in a severe impact, causing a short in the system. This short can trick the SRS into thinking the ignition is on, and to set off the airbags.

Interestingly enough, you should not assume that the airbags will not deploy even after disconnecting the battery. There may be other systems such as GPS or a cell phone that could potentially back feed the system to supply an ignition source. Static electricity can also set off an airbag.

The SRS is a very sensitive system, and engineers are still improving upon it. Foruntely, I have not had an airbag deploy in any circumstance for me, so I can give little first-hand experience on this matter. But what I've mentioned should give you some valuable information.
Good luck!