Funny enough, the one I've actually been around going off in a car was with me driving and no passenger. For whatever reason, the passenger bag popped but not the driver(and no, there was nothing sitting in the passenger seat). I was glad of that as it wasn't a terrible collision(the front end of the car looked nasty but it was driveable aside from a cracked t-stat housing). I was 100% unscathed without the bag aside from being a little sore the next day, and expect that the bag might have hurt me worse. The seatbelt tensioner did fire.
In any case, I knew the accident was coming, and basically went painfully deaf as I watched the windshield crash and spiderweb in front of me. I barely caught the bag inflating out of the corner of my eye, but it was mostly flat by the time I looked over at it a second or two later. My ears were ringing for the rest of the day. The broken windshield was not from the accident, but from the passenger bag. Those pack a whollop-I'm told more than the driver bag since they are larger to take up the greater space between the seat and dash vs. the steering wheel. The cracked windshield is supposedly normal for passenger bags also.
One of my college friends had grown up working in a body shop his dad owned. He brought airbags frequently and-under the supervision of a professor-we'd pop them on the front lawn of the college. Maybe it wasn't the smartest thing, but we'd run about 30ft of wire to them and they'd normally go off from a lantern battery. We would put them bag down and the bag+housing would fly probably 15-30 ft in the air. We did a fair few 90s GM driver bags which were reliable and repeatable. One of the most specatular ones was a passenger bag from a Kia. Granted from what I understand now bags are "smart" and the car can vary the deployment force as appropriate for the accident. We did a few side curtains also, but they were kind of boring. As best as we could tell, they're not pyrotechnic like the front ones, but seem to have a cylinder of gas that gets released to inflate them. They're slower than front ones, and also seem to stay inflated for a while.
Airbags save a lot of lives in serious collisions, but they're also nasty business when they do go off. They're definitely worthy of respect, and as much as I enjoy working on my own cars that's one thing I'd never do myself.