Titanic's Watertight Doors and Bulkheads
All the transverse bulkheads were carried up watertight to at least the height of  E deck.  Bulkheads A and B, and all
bulkheads from K to P, inclusive, further extended watertight up to the underside of D deck. (Bulkhead A further extended
to C deck, but it was watertight only to D deck.)

Bulkheads A and B forward, and P aft, had no openings in them. All the other bulkheads had openings in them, which
were fitted with watertight doors. Bulkheads D to O, inclusive, had each a vertical sliding watertight door at the level of the
floor of the engine and boiler rooms for the use of the engineers and firemen. On the Orlop deck there was one door, on
bulkhead N, for access to the refrigerator rooms. On G deck there were no watertight doors in the bulkheads. On both the
F and E decks nearly all the bulkheads had watertight doors, mainly for giving communication between the different blocks
of passenger accommodation. All the doors, except those in the engine rooms and boiler rooms, were
horizontal sliding
doors workable by hand both at the door and at the deck above.

The diagram below shows the location of all watertight doors [
shown in red] on Titanic.
The 12 doors immediately above the inner bottom in the engine and boiler room spaces worked vertically. They closed by
gravity, and were held in the open position by a clutch which could be released by means of a powerful electro-magnet
controlled from the bridge. In the event of accident, or at any time when it might be considered desirable, the officer on
duty could throw an electric switch and close all 12 doors. Each one of these doors could also be closed from below by
operating a hand lever fitted alongside the doors which released the clutches. As a further precaution floats were provided
beneath the floor level, which in the event of water accidentally entering any of the compartments, automatically lifted and
released the clutches, thereby permitting the doors in that particular compartment to close if they had not already been
dropped by any other means. These doors were fitted with cataracts which controlled the speed of closing. The time
required for the doors to close was between 25 and 30 seconds. Due notice of closing from the bridge was given by a
warning bell. A ladder or escape was provided in each boiler room, engine room, and similar watertight compartment, in
order that the closing of the doors at any time would not imprison the men working there.

The watertight doors on E deck were of the horizontal pattern, with wrought steel door plates. Those on F deck and the
one aft on the Orlop deck were of similar type, but had cast iron door plates of heavy section and strongly ribbed. Each of
these horizontal sliding doors, and each of the vertical doors on the tank top level could be operated by ordinary hand gear
from the deck above the top of the watertight bulkhead, and from a position on the next deck above, almost directly above
the door. To facilitate the quick closing of the doors, plates were affixed in suitable positions on the sides of the alleyways
indicating the positions of the deck plates, and a box spanner was provided for each door, hanging in suitable clips
alongside the deck plate.