RSP

* See also Depth
* See also Construction
* See also Real Physics
* See also UnderWater_Construction
* See also Tunnels
* See also Airlocks
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"RSP" Pressure Would Be Sea Level Normal :
14.7 pounds per square inch ( One Atmosphere ) 
There is no point in making it anything higher, as whatever it was it would afford no real construction benefits. Someone might suggest 'cheaper' at pressure solutions which simply 'Would Not Work', as you will shift a whole Atmosphere of pressure by simply moving just 34 feet up or down in Depth. So, any advantage would be only local, and all the massive pressure protection would STILL BE REQUIRED for the rest of Rapture. You would also face constant pressure changes for which the human body was not designed to handle.
Sea Level Pressure offers an environment with the LEAST health effects upon the inhabitants.
Rapture's entire structure would thus be required to maintain its 'Pressure Integrity' to be able to be conveniently inhabited.
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Note for Infinite BS : There IS NO 'Columbia Standard Pressure', and asphyxiation and altitude sickness would be chronic within the Magic_FantasyFantasy Population. 
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