Reading all this made me realize: Convertible cars/trucks don't have a chance underwater, do they? The passengers would find the top flattened down on them in an instant.
OK, I'm scratching my head on this. Really, if the roof of a convertible "collapsed," wouldn't that be just some cloth bumping your head? Just cut it open (yeah, it's tough cloth, but softer than steel).
I think no matter what, odds are pretty against you if you take an unexpected fall and end up underwater.
The Mythbusters episode where they tested this found that even under controlled conditions it was very difficult to escape in the time you could hold your breath, and that even in a controlled environment anxiety played a large role.
In the end, they had to do it a couple of times before he could relax enough to wait for the pressure to equalize.
If I recall, there were two successful modes of *opening* the door. One was if you pushed it open as soon as you hit the water. It took a lot of effort and wore the subject out. It only worked if he started almost the instant he hit.
The other mode was to wait for the water to equalize. I think they found if you struggled with the door too soon, you didn't have enough O2 to do it. You had to wait "calmly" until the right time.
I doubt many of us will have the chance to practice. So, if dropped 60' into the water while sitting in traffic, I'd say we'd all be pretty anxiety ridden and disoriented. Then, get it right the first time?
And the door opening trick depends on the door not being blocked by debris. In a controlled experiment there was nothing blocking the door. In bridge wreckage or simply on the bottom of a river, I'd say chances are good that there will be obstructions to opening your door. And even if only one door is blocked, if you spend all your energy and air trying to open the wrong one, you likely won't be able to try again.
They tried to break the window and they could not kick it out. The window punch worked.
Convertible?
Well, if the car was upside down, you'd be hosed.
If it was right side up, it *might* collapse and it might not. If it collapsed, I think this be pretty bad and add significantly to the disorientation. It would probably be pitch black (and it's going to be dark anyway), and you'd have no air reserve. The wind would probably be knocked out of you when you hit. Bad times.
It might not collapse, esp. if the windows were down. If the top were down and the car was upright, we enter into new territory.
If you hit and sink quickly, instead of having a 30 second air reserve, you are immediately under water. I suppose this would be the same if you had the windows down. In this case, I think things really depend on how stunned you are from hitting and how quickly you can regain your senses.
You probably could use the punch to break the laminated side glass and then kick it out. Once it is broken, it loses it's stiffness, and you could probably push it out. This doesn't work on the front because it is sealed all the way around. On the side it is only attached on the bottom and in tracks on the sides and tops. Kicking it should allow it to flex enough to come out of the tracks. But I sure wouldn't want to try it.
Laminated glass can also be cut after broken. If you had a large fixed bladed knife you could hack out a hole after it is broken. But this takes a lot of effort and doesn't seem very practical.
No matter which way you slice it, this is a bad scenario. The only thing we have evidence with is that the punch is about the best way to get out of a "normal" car. Laminated side glass seems like it would be a very bad thing in this case but the punch might help also.
FWIW, even though Mythbusters is on iTunes, they didn't seem to have that episode on-line yet. Maybe in the future they will.
-john
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