Answer SSEP Question 31

Q31. Define briefly the construction details peculiar to each of the following types of closure that enables their primary function to be fully realized:

A. Water tight doors;

B. Fire proof doors;

C. Gas tight doors,

D. State why (A) can perform function of (B) as well as of (C), whereas function of (B) and (C) are restricted solely to their primary function.

Answer: A. Water Tight Doors
Watertight doors are provided where an opening in a watertight bulkhead is essential. On cargo ships with a shaft tunnel, the entrance would have a watertight door fitted. Where as in passenger ships have different criteria by SOLAS, Passenger ships have longer engine room compared to a cargo ship. Most of the passenger ships have the lower most deck as engine room where the length of the engine room is as good as the ship's length. All doors fitted below the waterline must be of the sliding type, arranged horizontally or vertically.  The robust frame fits into the bulkhead and provides the track way along which the door slides. The door is moved by a hydraulic cylinder which may be power or manually operated. The door must be arranged for local opening and closing as well as operation from a point above the bulkhead deck. WTD's must be built to withstand flooding and the head of water created. The W.T door to the tunnel is generally heavy and hand operated, cast or fabricated, vertically or horizontally sliding door which close positively into a taper or wedge for a metal to metal water tight seal, need not be insulated. Power may be used for operation with remote control as well as local control from either side. The positive closing is by screw shaft or hydraulic rams, in all cases the door should be capable of closing against 15 deg of heel with dissimilar metals being used to prevent seizing. Audible alarm during closure by remote power shall sound for at least 5 second but not more than 10 seconds before the door begins to move and continue power shall be from ESB through dedicated distribution board situated above bulkhead deck can be capable of being automatically supplied by emergency source in event of failure of main or emergency power. 
Peculiar characteristics of water tight doors
Peculiar characteristics of water tight doors are, they are designed mainly to prevent the ingress of water from one compartment to another in case of any flooding in the adjacent compartments,
Their peculiar characteristics are:
(1) When the door is closed, it is usually locked against respective frames by wedges, in order to achieve a close tight fitting between doors and frame itself.
(2) To ensure water tightness usually it is implemented by a special profile brass packing in which, a special graphite gasket is inserted and fixed by screws.
(3) Suitable guides are fitted on upper and lower sides of the frame, which will guarantee the proper sliding of doors under whatever operating condition.
(4) Doors are usually provided with wheels and bronze bushes for bearing capabilities

B. Fire Proof Doors
(1) Fire proof doors are normally provided at Strategic locations throughout the ship. Where there is frequent use, the doors are normally held open by electromagnetic latches and closed by a spring. In some ships, large sliding doors are pneumatically operated; they will close automatically on failure of air pressure.
(2) The doors are located so as to:
(a) Isolate each fire zone from the next, this being achieved by fire doors in main passageways in way of bulkheads which from fire zone (Vertical sub division) boundaries.
(b) Close off the boundaries to stairways, lifts and elevators so as to maintain safety escape routes within each zone in a vertical direction.
(3) As par SOlAS74 Chapter II -2 Regulation 9 Fire proof doors are fitted above water line and in accommodation space suitably manufactured with insulation being fire retardant material classed A class & B class division in accordance with the fire test procedure code. For e.g. in galley and service space. Hold back hook are not permitted to keep the door in open position.
(4) These doors are comparatively lighter in construction to that of the W.T. doors, held in open position by a solenoid energized magnetic switch connected to the fire alarm circuit. In event of these fire switches set de-energised and close the door with fire alarm. peculiar Characteristics of Fire Proof Doors
(1) As Fire proof door, it is made of fire retardant material.
(2) Fire door material will match to that of the adjacent wall or bulkhead so as to provide same protection that of a wall or bulkhead it is attached to.
(3) Fire proof doors are Just a replacement to normal door but with additional security for above mentioned purposes; withheld open by electromagnets and designed to prevent the passage of smoke.
C. Gas Tight Doors
These doors are fitted on the weather deck entry into accommodation and in super structure areas. They are made of wood lighter in construction compared to W.T or fire doors with thin aluminium/steel sheathing providing a gas tight sea. These doors are opened and closed manually.
Peculiar Characteristics of Fire Proof Door
 As Gas tight doors are made of a special wood material to prevent any gas ingress through it while it is properly closed and latched.
D. State why (a) can perform and function of (b) as well as of (c), whereas function of (b) and (c) are restricted solely to their primary function.
These among all three doors mentioned above, W.T doors are robust in construction of steel and fitted in machinery space prone to fire, flooding and smoke, hence prevents the passage of flame and smoke. Thus, it does the function of fire and as tight door duties. Whereas fire doors are lighter in construction fitted above the bulk head deck, preventing the passage of flame and smoke providing a gas tight sealing and thus functioning as gas tight doors also. They are provided in the accommodation spaces, galley boundaries and stair case areas. The gas tight doors are also lighter in construction and only meant for providing gas tight sealing, but cannot perform the function of watertight door or a fire door.