How Deep At 250Mbar Pressure One For The Divers Out There

[smiffffffy]

If a waterproof zipper says it is airtight to 250 mbar, how deep would this allow you to go in sea water before it would be ineffective and leak.
( in perfect scenarios )

I assume there is a difference in depth between salt water and freshwater, not sure why i may think that, ( dead sea floating i suppose, more salt better buoaynacy) .

similarly if a product is then rated at 500mbar or 750mbar, does the depth achieved double and then treble ??

[Clanad]

1 millibar = 0.03348831726564 foot water at 60°F… you do the math...