During the diving scenes they speak of a pressure of 40 atmosphere this would put them at a depth of around 390m/1170ft. Even if you suppose the large inlet pipes are filled with water and go down 47m like said in the series, that would only put the divers at around 6 atmosphere.
When Nairobi comes down the stairs to talk to the hostages, you can clearly hear that the stairs are wooden, despite looking like made from stone. They are a constructed set, as is the whole lobby.