Securis

* See also Watertight_Doors_and_Bulkheads
* See also Rapture Construction
* See also UnderWater_Construction
* See also Airlocks
== Securis And Other Doors ==
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Those big pedestrian doors you frequently go through during the game.
They are supposed to represent Pressure Doors (which are able to withstand being subjected to the deep water pressures (280 lb/sq in at 600 feet down).
They have a rotating lock mechanism which apparently sets locking bolt into place in the doors necessarily heavy metal frame to prevent accidental opening.
I have postulated that those doors are a bit more complicated. Because their needing to be so heavy due to the thickness of metal required, actually have two additional outer cosmetic doors (what you see moving) with a VERY HEAVY pressure door between them, which ONLY deploys when a Pressure Event occurs (a major leak imperils the locale).
Thus quick opening and closing of the cosmetic doors (which serve to keep the space between them clear for when that middle Pressure Door/Bulkhead may need to be deployed.
PIX
Securis Doors - why have those spinning things (an airseal, but the mechanism can't be horrendously heavy and constantly open and close). The integral Heavy Pressure Bulkhead is a simpler mechanism deployed ONLY on emergency (Doesn't have to reopen constantly/quickly). Its also cheaper - we saw alot of these.
The two outer doors (that Securis look, which open and close constantly/quickly) act as guard doors to prevent blockage to keep clear the Bulkhead closure. They prevent fire/minor-water spread.
Might that Securis rotation locking feature thing be to sweep stuff out of the way (of the Pressure Bulkhead seals) ??
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Aluminum alloy doors can be of similar strength, but still need to be heavy/massive enuf to attain the full structural strength required. Titanium was TOO difficult to work in 1946-1952 .
The Airseal doors could be Aluminium, but that material is rather poor for Fire Containment doors (works for smoke).
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Securis Safety Doors Redundancy :
* We saw, playing BS1/BS2, several Securis doors fail/partially fail (dramatic but would spell doom to the City if they failed that easily).
* A standard engineering Rule of Thumb is to over-engineer to 300% (at least in the old days). Much of Rapture would have been built to something more like 600%, with redundancy built into ALL critical systems/structures due to the potential disaster of any failure (its another reason why the place is still largely intact).
* Thus those Securis doors actually would have an integral second automatic emergency door (2 inch steel plate that slides across and seals the opening in a slot on one side).
* A SIMPLE pressure differential mechanism would activate the second door closure no matter what state the primary door was in. Opening it later after this emergency door was once triggered would be a significant effort, but that would be under controlled (supervised) circumstances. The doors automatically closing and locking securely - reliably is its primary function.
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Securis Door Details
The Visible door is only a small part of the Securis Door mechanism. The 7 by 5 foot doorway would have the door extend another foot around all its edge, The Door slides within a heavy metal frame to brace the door 'securely' against the likely pressure (280 lb/sq in at 600 feet deep). The frame is set and anchored strongly into the buildings concrete structure. 
The original Securis doors (the ones with those rotating thing-a-ma-jigs) are shown to move quite fast while opening/closing (they need to move that fast for normal human traffic usage). The game doors are shown to be about 6+ inches thick. Even a door of 1 inch thick Steel alloy plate (still too light for the pressures and dimensions involved) would weigh over 2400 lb (Steel 1 inch thick weighs >40 lb/square foot). Moving that much heavy mass (or more) rapidly and repeatedly takes a large/complex/expensive mechanism, Such would be subject to significant maintenance/malfunction problems. THAT mechanism would be problematical.
My modified design has a pair of outer Airseal doors, which being far lighter (mere hundreds of pounds) CAN move sufficiently fast while using a reasonably sized actuator mechanism. These Normally Closed outer doors will block fire and transit while closed, but open/close quickly for their frequent use.
This revised design NOW incorporates BETWEEN the two Airseal doors a heavy pressure resistant Bulkhead -- which NORMALLY DOES NOT MOVE. This inner door is only to be deployed during an (EPS) Emergency Pressure Situation (ex - a major leak caused by building primary structural failure and loss of water integrity). The Securis portal protection mechanism can now be sufficiently STRONG and HEAVY (as in the moveable Bulkhead weighing several tons) without complicating the game-shown Securis door operation. 
Like other emergency Bulkheads (ie- the bigger ones for Rapture's Trolley connections), it does NOT have to be reopened fast (It is to be manually reset only AFTER the emergency situation has been properly rectified).
An All-metal solid frame surrounds this Bulkhead (and all its mechanism) to provide the required structural strength, and a tight fit/seal. That frame is strongly embedded and reinforced into the building's primary Ferro-concrete structure.
The Bulkhead/frame sides have multiple stepped groove/slots as part its design, acting to seal the edges, and to transmit the water pressure force put on the Bulkhead's 35 square foot face (which IS possible from either side of the portal - since a catastrophic leak could happen from either direction).
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The interior design of the Bulkhead has opposing 'arched' reinforcements, with sufficient depth dimensions to transmit the massive pressure forces fully upon either of its flat surfaces. The doorway's 35 square feet area equals 5040 square inches. 5040 square inches with a surface pressure of ~280lb/sq in (of an assumed depth of Rapture 600 feet down) is : 1,411,200 lb (~750 tons) of force distributed over that door surface -- If pressure containment fails in the building's primary structure. The indirectly supported center of the door is subjected to a great deal of leverage force (increasing towards its middle) - thus requiring the design's significant reinforcement to distribute that force to the frame and surrounding building structure.
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Flat metal deck plate 'flaps' (which provide a flat/flush walking surface) open out of the way when the Bulkhead is lowered (it has to seal tightly at its bottom receiver frame) using a simple robust leverage rotation mechanism. Upper cosmetic flaps are merely spring-loaded and are pushed out of the way.
Those deck flaps prevent any clutter of material from blocking the Bulkhead's activation movement. When an emergency closure happens, the Airseal doors are locked closed preventing immediate blockage of the Bulkhead's movement path. But regardless of minor impediments, the Bulkhead soon closes.
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Pistons are used to mechanically force this heavy Bulkhead closed (and because it moves downward this is also assisted by gravity). Such Pistons HAVE to be at least as long as the door is high, adding to the overall size of the entire mechanism.
These Pistons would be actuated by simple chemical cartridges to generate gas pressure to move the Bulkhead's mass and force the bottom edge into the receiving frame - generate a sufficient seal. The Bulkheads need to operate in failure situations, which precludes electric driving of the closing movement. ( A simple hand cranked mechanism probably would be used to 'Reset' (open) the Bulkhead - as no speed is needed for that. ) The Piston system is triple redundant. Each Piston, by itself, has the capacity to operate the Bulkhead. 
The Bulkhead closing-movement would have sufficient force to crush many ordinary item(s) and still seal the Bulkhead adequately. In event of a minor leak from an imperfect seal, the mechanism would still allow sufficient time for evacuation/repairs ( It would be well within the capacity of every buildings drainage pump system to handle ).
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Note how large the entire mechanism is. It has to be at least 3 X the total height of the visible doorway to accommodate the space for the (open) recessed door and its mechanisms. This might be problematic for some of the game's level maps, which didn't allow the vertical space (but game doors don't HAVE to really work (or be designed to work) after all, do they?). Sideways moving major doors/Bulkheads would require similar mechanisms/hidden workings ( and likewise block placement of adjacent wall windows, to one side ).
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The Airseal doors would likely employ a pinion gear/rack mechanism to routinely open/close the 'doors' quickly/repeatedly using electric motors ( and have a backup manual crank for power failures ). The door's Activation Sensor would operate via electric eye/floor-pressure-plate, giving it that modern/advanced aspect for the game ( and to not have the Player/NPCs constantly have to open all the doors ).
The Bulkhead Emergency activation works automatically using (redundant) mechanical pressure trip valves, which on a sudden significant increase in pressure will activate the Bulkhead ( you don't want them too sensitive so they activate when someone flushed a toilet ). Additional mechanisms allow Remote activation from central control points and from multiple additional automatic electric-operated Sensors.
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Something usually totally ignored : Any complex door like this NEEDS access to its mechanism for maintenance/repair. With these Securis Portal Doors, an added aspect is that the whole Mechanism HAS TO BE hardened against the potential forces the door is to resist ( leak water pressure in excess of ~280 pounds per square inch ). SO the actuating mechanism must be well protected, and any/all maintenance access would be similarly protected.
Safety mechanisms : Edge sensors to keep the Airseal door from closing on something/someone ( another reason for having electric activators ). Alarm Warning ( flashing light, etc ... ) for Emergency Event closing ( a serious thing as it means a catastrophic leak ). 
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Through the Gold Plated Door you get a Tour of the Chocolate Factory ???
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Securis Door Design :
The doors are designed to hold an excess of the water depth pressure from either side, and to Close and Seal successfully even if there is debris in the way.   The doors we constantly seen opening and closing are NOT their Primary pressure seal doors.  Instead, what we see are lighter 'outer doors' -- which normally keep the primary door's seal slot free of blockage.  The Primary pressure-proof doors are made of a light/strong titanium alloy, but still weigh well over a ton ( a bit too heavy to constantly open and close quickly on a Citizen's whim in their normal use ).  The Primary Door only slams down on pressure seal activation.  
A hydraulic ram has sufficient force to drive the blade edge of this door panel thru most common objects and past its receiver slot, forming a proper seal.   The heavy Primary Door structure design has double curved structural plates ')(' welded together, which redirects the surface force into the heavily anchored door frame structure, using both compression on one plate (like an arch) and tension support on the other  ( like a suspension bridge ).
Seals are always a problem for high pressure situations ( the smallest gap will STILL continue to have huge amounts of water spewing through at high pressure ). This problem is solved by using the force of the water itself to press the door against the frame it sits in, with semi-malleable seal materials being deformed to tightly form a seal ( the reason THIS cannot happen every opening and closing ).  A softer material which can deform and close off the  open space ( required for the door to slide easily ) coats the seal surfaces.  Once the Primary Door is engaged, and the water force presses upon it, very little water will get through.
Perhaps An expensive Titanium alloy was used on the standard doors because of its high strength ( three times as strong as steel per volume and being 3/7 ths lighter in weight ).  This Titanium use WOULD require a technological acceleration for 1945 - a significant "Wave _of_the_hand".
Aluminum ( with the same strength as Steel, but at 1/3 the weight ) in one thick slab, is an alternative for doors upto a certain limited size ( ones smaller than the typical 6 foot wide, 7 foot tall Securis door opening --- Like the many maintenance hatches and utility fail-safe bulkheads used in Rapture ).
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A submarine door is usually designed to act against pressure on both sides.  Securis doors also are meant to secure from pressure from either direction ( since you don't know where the failure is going to be ).  Submarine doors are also usually smaller, shorter and half the width of the standard Securis door.  The bigger the door, the more cumulative force will push against it ( and the frame it is mounted in ).
http://3dconceptualdesigner.blogspot.com/2012/11/3d-model-sales-part-iv-submarine.html
There should be an alarm for any door being held open and a bypass if the pressure sensor triggers the doors closing. ( Chopping one person in half is preferable to hundreds of deaths ).
There are Bulkhead doors much larger than the standard 6 foot by 7 foot tall standard Securis, which have similar construction - except they span a larger area and thus are thicker and far heavier.  They normally stand open ( do not open and close ) and more of their function is dedicated to closing and fully sealing to protect flooding from spreading through large areas.  Reopening them usually takes significant work and override by authorized personnel.  
Standard Structural safety regulations (and maintenance) were enforced by the City ( not left up to local citizens/building owners ) because failure effects more than just the immediate vicinity/people.  Much building was done by Ryan to His Standards, and other construction was required to adhere to ALL the safety systems.
The abysmal showing of Securis doors failing at Sirens Alley in BS2 really wouldn't happen ( and having the doors tampered with well ahead of time by Lamb just in case YOU showed up would be ludicrous ). The thing truly stupid there : ( ie- seen in Sirens Alley ) Was the Airlock to the outside having both doors simultaneously (supposedly) be 'Open to the Sea' -- They would SPECIFICALLY be designed NOT TO EVER allow that to happen under ANY circumstances.   You literally would then have to destroy both doors to force them open like that.   Every bit of the door's design would be to prevent anything like THAT story foolishness happening either by accident or design.  Securis doors would likewise have such Fail-safes, and it would be unlikely any kind of remote override would be allowed to exist ( and NO, they are not all remotely controlled by The Thinker - a simple electric eye system works just fine for  1/10000 the cost ).     
(( But maybe this is like the bizarro-land magnetic hook jumping in Infinite BS - some Devs storyboard 'good idea', 'Cuz' it will be dah 'neat' thing ...  Major/Minor stupid details don't matter to hack game writers. -- The MMORPG WOULD DO AWAY WITH SUCH TRASH )).
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 Will You Kindly Open The Door ? :
* Fewer automatic doors in the MMORPG game - The electric eyes and other trigger mechanisms wont be working thru most of the  wrecked areas of the city.
* The City Center 'beautification' would have them ALL working again, and they would eventually get fixed throughout the  'Downtown' parts of New Rapture ( outside of that, it will upto whoever wishes to fix them ).
* This excludes the Pressure Seal doors that will be made to work before Citizens are permitted to take residence in an Area (Safety Regulations).
* Restoring automatic door function would be a 'routine' Maintenance mission/quest.
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Securis - Warrantees Must've Expired :
Those Securis Doors in Welcome Center are a bit too failure prone the way they buckle ( when they are 6 inch thick doors - when 1 inch steel plate of that size will hold up to that kind of pressure ). The viaduct the plane tail-section crashed and broke into likewise was kinda weak for the pressure that the structure normally puts up with ( airplanes are built like tin-foil to be light enough to fly ). The large hole stove-in would have water pour in so fast and compressed the air in that viaduct to 1/19th of its previous volume virtually instantaneously. But remember the Hack Writer Creed : "Never let Physics or Reality get in the way of the Plot" ... 
Fine Print : Regular Maintenance Must Be Maintained
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Damaged, But Holding
A damaged Securis door seems to be buckling. But as I explain and illustrate above, there are thin cosmetic doors around a very solid main Seal Door. That Seal Door looks to have deployed. Here you have partial leakage, but the level's pumps seem to be keeping up with it.
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Some Of The "Securis" Doors Seen In-game BOTCHED by Developers :
Look for locations ( the doors come down when they close, up to open ) where there isn't sufficient interior (inside wall) space for the mechanism or even the door itself ( It is supposed to be a door that seals against 600 ft - 280 psi pressure of water - Very substantial, so such a door NEEDS to be properly embedded in the thick supporting wall/floor/ceiling ).
pix in MD one in MD_0
Consider : game Level Devs have deadlines too ( one wonders if they had a proper Emulator of the Game Engine to even see defects (A MISTAKE THE MMORPG EDITING SYSTEM WOULDN'T MAKE - as scripted placement logic for door objects would include the proper criteria checks ).
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