There is obviously some good life saving advice, the most important of which is to get your windows down and get out fast (even electric windows will work for a while - contrary to what the video says). Also useful is carrying a center punch in your glove compartment (a machine shop center punch which you can get at a hardware store will do) for easily breaking the window.
Unfortunately, the video perpetuates a myth that you will be able to open the car door once the cabin is fill with water. This isn't precisely right. First, they are right that you won't be able to open the door if there is still air inside the car, but they are wrong in implying that you are guaranteed able to open the door once the cabin is full of water. This will only be true shortly after the car has hit bottom! So, if you are talking a deep body of water, and you have waited until the water level is at the windows, and you have no way of breaking the windows ... well, you're dead!
Here's the Mercer video.
The issue is the difference in pressure between the outside and the inside of the car. Water pressure is more than enough to prevent you from being able to open the door, or roll down the window for that matter. What is often missed is that water pressure builds rapidly as you descend, so if the car is full of water, but the car is still in the process of sinking, the pressure on the outside is still building and will be higher than the pressure on the inside. The pressure will not begin to equalize until after you've hit bottom.
The issue was also explored on an episode of Mythbusters. Unfortunately, they missed this little bit of physics too. Thus, they repeated the deadly myth that you will be able to get out of your car once the cabin is full.
Thankfully, there is one television program that got this right. The next clip is from the British car show, Top Gear.
So, if you find yourself in this deadly situation, roll down the windows and get the hell out FAST! If you wait, it could easily mean you wont be getting out at all.
