# Why doesn't soda fizz at high pressure?

In this video, a can of soda is opened in an underwater station at 2.5 atm. The demonstration is that shaking the soda doesn't cause it to explode like it would at normal pressures.

Why does this work? Is it because the pressure inside the soda can is approximately equal to the pressure inside the station?

Also, will the soda be effervescent, or is it completely flat?

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At the 27s mark he comments after taking a sip that there is a little bit of fiz. –  Dan Neely May 15 '13 at 17:27
Yeah, he does. I was wondering if it would have significantly less fizz. My guess is no. –  Kris Harper May 15 '13 at 17:51
If he hadn't shook it up first I'd expect much less fizz due to the much lower difference between pressure the dissolved CO2 was saturated at and the atmosphere. With the can being shook up I don't think it would be answerable without a lot of of math. A a minimum we'd need to know the actual pressure in the unopened can, and have a way to calculate how shaking the can accelerates the rate of gas release. (I have no idea how to do this.) –  Dan Neely May 15 '13 at 17:59
Wait, but that means the people inside the submarine are experiencing the pressure too, right? I mean, if it caused the soda to not fizz as much, how are the people not affected? They aren't even wearing any gear to tolerate the pressure with. –  mikhailcazi Jul 3 '13 at 13:05

The pressure inside a can of soda is around 2 to 3 atmospheres (above ambient i.e. 3 - 4 atmospheres total) depending on who you believe. The solubility of CO$_2$ increases with pressure, so when you open the can the pressure immediately drops by 2 - 3 atmospheres, i.e. by a factor of 3 to 4. As a result the solubility of the CO$_2$ decreases and the excess CO$_2$ comes rapidly out of solution as gas bubbles.
In the underwater station at 2.5 atm the pressure difference is only 0.5 - 1.5 atmospheres, so when you open the can the pressure decreases by a much smaller amount i.e. by a factor of only 17% to 33% compared to a factor of 2 to 3 at surface pressures. Accordingly the solubility of the CO$_2$ decreases by a much smaller amount. Excess gas will come out, but much less and much more slowly.