Side/window Air Bag problems of the 2001 Volvo V70

After a side impact the side/curtain air bags failed to deploy. Impact to the passenger rear and front door. The impact was between 30-35 miles per hour.

The road: 2 lanes each way, wide median, paved shoulders which rolled off into a drainage ditch, 60 mph limit with sto plights. While in left began to pass vehicle2 [SUV] in right lane. Vehicle 2 moved into left lane forcing me onto shoulder. While on shoulder and attempting to reenter lane after completing pass began to lose control of car. That was the last memory of the events leading up to the accident. At this point, I believe that the driver's airbag deployed prematurely. It knocked me uncouncious, preventing me from trying to control the car. The car ended up crossing the road to the right shoulder. It left the roadway at 20-30 degree angle. It went down into a ditch, and rolled up a bank 2-3 times. It came to rest on the driver's side. The upper passenger side was crushed, and the car was totaled. The roof of the car was cut so that I could get out rather than crawl through the windshield. The side impact airbags did not deploy in the rollover. The passenger airbag did deploy. My shoulder/seat belt was on. I was extremely fortunate to only have minor injuries. How can I indisputably determine when the airbag deployed? is there a data recorder? do I need to hire an accident investigator?.