On the other hand, you’ll have no real chance to tell if the air is escaping or compressing. Also, since it takes 33′ (10m) to generate 1 ATM of pressure differential (in freshwater), if you’re only down 3-4 m, you’ll probably be okay in any event. And even if you did suffer some damage because you held your breath after breathing some compressed air and came up from a notable depth, you’d still be better off than drowning as long as someone could adminster oxygen and they could get you off to a hyperbaric chamber soonish.

Still, it won’t *hurt* you to slowly exhale a small stream of bubbles as you ascend. Small bubbles, slow stream to give you time to get to the surface.

2) The lifehammer and other similar things work on the idea of force applied over surface area of application. They apply very large forces/unit area because of the sharp point of their delivery. Keys might work, but try punching a board with your keys point out. It’ll probably do your hand some damage. Better to have a reliable rescue tool. At $15, you can’t really argue against the value if you ever need it.

3) To be safest, get some training from your local FD or paramedics on vehicle extrication. Hard to practice if the use of the tool cuts belts and smashes windows, but you should practice unbelting, acquiring the tool, and the rough motions with the eyes closed. Extricating yourself through a window could be challenging for some if they are short like me and fit tightly into place – I’d want to tilt the steering away and move the seat back if possible.
Getting out through a shattered window is a bit like a wet exit in a flipped kayak and that’s a bit exciting if you’ve never done it for real before.

4) Seatbelts, if you are hanging upside down or they’ve taken some damage, may jam. You might not be able to unbuckle, thus trapping you and/or preventing you using the seat belt as a hammer. Something like the lifehammer or resQme should be within *arms reach while belted*. Then you can cut away (probably that would be exciting if you’re upside down also… fall on head on car roof in confined space won’t be fun, but it will be necessary).

5) Pressure outside from water is both good and bad. More of it means likely more water pushing into the vehicle from any point it can intrude (eventually any seals will fail). But it also means that the pressure on a window to fail is greater, so a smaller crack in the glass should yield window disintegration. Of course, the more water pressure, probably the more cold (from depth) and force (in your face) you’ll face when the window goes. Nothing like being kicked in the head by a wall of water… so get out sooner rather than later. But if you have no option and are submerged, probably face away from the window, put your chin on your shoulder to stabilize your head, and shatter the window. That’s the best chance of not getting knocked out or stunned by an inrush of water at significant depth I’d imagine.

6) If all else fails, try keys, try seat belt edge, if you’ve got a brass-barrel or steel-barrel fountain pen, use that to strike the window – anything that can help generate signifcant force on a small area (hatchet, knife point for hunting or pocket knife, etc).

Failing having any tools, if you can get a forearm lined up, try to strike hard with the tip of the elbow, moving from the shoulder with your body weight. Or fold your fingers at the second knuckle (tiger’s paw) and drive with that – likely to break some knuckles, but it might crack the glass. These are VERY desperate measures – far better to have the $15 lifehammer.

No, I don’t work for these guys, I just recognize a key safety tool for a good price.

And remember, the best lifesaver in a crisis is not panicking – immediately focus on the critical next step to saving yourself, don’t think about anything else, and act swiftly but deliberately. Deliberate action, a cool head, and a focus on ‘what do I do next?’ is the best odds of coming out in one piece.

If I remember correctly, they used weights to simulate the pressure of the water pushing down on the power window. The power window was not able to open because it would need a great deal of force to slide the weights sideways due to friction.

I hope Mythbusters revisits this myth.

for lance, pony bottles (the little bottles of back up air) are available to the public, but because of the aforementioned potential dangers, as well as other things to keep in mind, you really should get scuba certified first. scuba diving is a lot of fun, and easy to learn.