Looking for the equation that explains why you can't open a safe underwater (like in The Italian Job)?

Question

It would require a lot of force to open a safe underwater, like they did in the Italian Job.

I am looking for an equation that would figure out how much force you will need to open an airtight container [such as a safe] underwater, also, under different depths.

Thanks

Answer 1

Water pressure is given by
p = rho*g*h
where
rho is density, of sea water in this case 1030 kg/m^3
g = 9.8 m/s^2
h is the depth.

Since pressure is force/area, the force keeping the door closed is
F = p*a
where a is the area of the door.

Answer 2

I don't know an equation off hand, however, the safe wasn't under that much water.

theres a similar problem involving Pirates of the Caribbean.
The part where they use the boat for an air supply under water.