Three floors without a fire escape seems rather unusual to me. Personally I´m no big fan of mandatory building codes but that doesn´t mean you have to disregard all safety. Are you sure your building complies with the relevant regulations, if any? I´m in Sweden by the way, perhaps it´s just our regulations that are extra draconian…
Well, if portholes on ships in general are openable, and the regulations say they should be, that would indicate that the consensus is that this is the safer way to go, on balance.
Even if you flood an entire floor through an open window that shouldn´t spell disaster. There should be bulkheads and waterproof doors between floors, right? And before it comes to this you should have some time to close the port. You could have alarms that go off when there is water on the floor, you could have centrally mounted indicators for open ports, you could have the portholes only openable as an emergency exit, with an alarm that goes off throughout the steastead when opened. Etc.
And in general, having them openable gives you more options. Yes, in some respects it increases the risks. But in other it decreases them. All things equal I´d rather go with the way that gives me more choices when the shit hits the fan, because it will, eventually.