The dangers of power-operated watertight doors
Gard News 207, August/October 2012
The following four articles in this issue of Gard News consider the dangers involved in the use of power-operated watertight doors in ships: the risks to personnel passing through these doors and the risks such doors represent to a ship in case of water ingress. People have been trapped, maimed and killed by power-operated watertight doors and in cases where these doors have been left open or leaking, they have contributed to the capsizing and sinking of ships.
Watertight doors are not a new invention; SS TITANIC had watertight doors, which closed vertically. In the well-known disaster involving that ship, the doors were not the main problem. The problem was the long rupture of the vessel's hull due to the contact with an iceberg breaching several subdivided areas - those subdividing bulkheads not connecting to a bulkhead deck, as is required today.
A vessel is subdivided by watertight bulkheads so it can survive ingress of water following a grounding or collision. The more watertight bulkheads there are, the lower the risk of the vessel capsizing and sinking if the underwater hull is punctured. A high number of bulkheads may, however, limit the commercial use of space on board and make it cumbersome for the crew to move around between the subdivided spaces. So watertight doors are fitted in subdivision bulkheads. These doors can be closed from the bridge for the purpose of saving the ship, and opened and closed on location, allowing personnel to pass through them during their work, as well as to escape in an emergency. Saving the ship is a priority, so the bridge can take control of all doors and close them.
Large number of watertight doors
The use of watertight doors in watertight bulkheads has been increasing. For years, 30 to 40 doors have been the norm in large cruise vessels, in the engine room, service areas and crew quarters below the waterline. In larger vessels the number of doors is steadily growing. There may be more than 5,000 passengers on board the largest cruise ships, served by a staff of more than 2,000. While spaces on higher decks are used for shopping malls, casinos, auditoriums, state rooms, restaurants, etc., lower decks are used for service facilities like food storage and handling, garbage handling, sewer treatment plants, laundries etc., as well as for crew cabins. These areas below the waterline and the bulkhead deck are subdivided by bulkheads fitted with watertight doors - a large number of doors, all prepared to close with a two ton force if ingress of water should threaten the vessel's safety. The new record in number of doors is probably two cruise vessels presently under construction, designed with no less than 74 watertight doors.
Engine rooms, which in most cargo vessels will pass through all the decks from the tanktop to the funnel, may only occupy space on the two lowermost decks in cruise vessels. This is done to make use of the space on higher decks for the benefit of the passengers. What such an engine room loses in height it will gain in length, and there are cruise vessels with a 200-metre-long machinery space to allow for the main engines, diesel generators and all necessary auxiliaries and support systems on board the vessel. Such a long engine room may pass through five or six transverse watertight bulkheads, all fitted with power-operated watertight doors. Some ships may also have two engine rooms for redundancy and thus also a longitudinal bulkhead, again with more watertight doors. Personnel on duty in such machinery spaces have to pass through a large number of doors while working, and each time go through safety procedures for opening and closing them. When having to pass through such doors repeatedly, one may be tempted to shortcut the safety procedures and pass through the doors before they are fully opened.
A large number of doors may also be found in Ro-Ro passenger vessels, ferries, in large supply ships, special purpose ships, crane ships, oil exploration vessels, etc., and also in mobile offshore units.
Watertight doors are often marketed as a feature that increases the safety of the ship, but it should be remembered that the bulkheads where the doors are fitted are required to be watertight, and any door or opening in such a bulkhead is thus a weakness of the watertight integrity of that bulkhead.
To make doors as safe as possible, both to the people passing through them and to the ship in case of flooding, such doors are regulated by SOLAS Chapter II, "Construction - Structure, subdivision and stability, machinery and electrical installations". There are regulations on safe operation of doors, control stations, alarms and signals, blackout redundancy, emergency opening and instructions to be provided.
SOLAS regulations concerning watertight doors
The SOLAS regulations discussed below are applicable to vessels built after 1st February 1992.
SOLAS Chapter II-1, Part B deals with "Subdivision and stability". Regulation 4.3 provides the general requirement that "Ships shall be as efficiently subdivided as is possible having regard to the nature of the service for which they are intended". The new SOLAS regulations on subdivision and damage stability are now based on a probabilistic concept, not that easy to understand, but for the purpose of this article let us just say that the longer the vessel, and the more passengers it carries, the higher the degree of subdivision required. Some transverse bulkheads are well defined in Part B-2, Regulation 12: there must be a collision bulkhead at a certain distance from the bow and a bulkhead at each end of the engine room. No doors or other openings are allowed in the collision bulkhead below the bulkhead deck, but SOLAS does not give such precisions for the engine room bulkheads, except that they are to be watertight up to the bulkhead deck, separating the machinery space from cargo and accommodation spaces.
Regulation 13.1 deals with openings in watertight bulkheads below the bulkhead deck in passenger ships: "The number of openings in watertight bulkheads shall be reduced to the minimum compatible with the design and proper working of the ship". But is this "reduced to the minimum" requirement observed by ship designers and authorities approving the designs, when vessels end up with such high numbers of doors as mentioned above?
In transverse bulkheads dividing cargo spaces in principle no doors are allowed, but may still be fitted if "the Administration is satisfied that such doors are essential" (Regulations 13.3 and 13.9.1).
Regulation 13-1.1 deals with openings in bulkheads in cargo ships, and, as for passenger ships, starts with a firm statement: "The number of openings in watertight subdivisions is to be kept to a minimum compatible with the design and proper working of the ship".
It would appear from the above that the regulators initially intended to have as few watertight doors as possible in subdivision bulkheads, regarding them as a certain risk, but that it has become relatively easy, depending on the policy of the flag state, to obtain a relaxation.
In addition to the SOLAS regulations, there are also requirements for a vessel's stability after damage and flooding in Regulation 27 of the 1966 Load Line Convention.
Watertight doors in offshore installations
Mobile offshore installations may have a large number of power-operated watertight doors, and the problems are the same as for ships. Regulations, however, are often much weaker than the SOLAS Convention and there is no international set of requirements. For mobile offshore drilling units there is the Code for the Construction and Equipment of Mobile Offshore Drilling Units, 2009 (the MODU Code), which has some requirements for watertight doors, but in far less detail than SOLAS, and which to most flag states serves just as guidance. Flag states and shelf states may have their own national regulations and some may adapt the principles of SOLAS.
Watertight doors of offshore units may be arranged to close in case of fire or gas detection, an added risk to personnel, as the doors will act as if in remote control mode. After opening, when the handle is released, the door will immediately start to close.
However, in Norway authorities seem to have a stricter approach to new regulations for offshore units than for ships. While one unfortunately still finds old operating systems for watertight doors in ships thanks to a grandfather clause, the Norwegian Maritime Authority requires that at five-yearly renewals of certificates mobile offshore units comply with the latest regulations. If there have been changes to the regulations since the last certificates were issued, the company must prepare and submit a gap-analysis to the authorities.
Operation and control of watertight doors
Power-operated sliding watertight doors may be hydraulically or electrically operated. Hydraulically operated ones must have either two independent power sources (each consisting of a motor and a pump) capable of closing all doors, or each door may have an independent hydraulic system. In both cases there must also be hydraulic accumulators capable of providing stored power to operate the doors at least three times, closed-open-closed, against an adverse list of 15 degrees. Electrically-operated doors must have an independent electrical system and motor for each door with the power source capable of being automatically supplied by the transitional source of emergency power. In the event of failure of either the main or the emergency source of power, doors must be able to operate at least three times, like for hydraulically-operated doors. There are low level alarms for the hydraulic fluid reservoirs and a low gas pressure alarm for stored energy accumulators. For electric systems there are monitoring and alarm systems for the power supply.
Watertight doors below the bulkhead deck can be closed from the bridge and can be opened and closed from the location of the door. The central operating console for watertight doors, both in cargo ships and passenger ships, is located on the bridge. This console is provided with a diagram showing the location of each door, with visual indicators to show whether each door is open or closed. A red light indicates that the door is fully open, and a green light that it is fully closed. When the door is closed remotely, the red light shall indicate the intermediate position by flashing. Unfortunately, older systems may have no definitions for red and green functions. SOLAS Chapter II-1, Regulation 13.8.3 states clearly that "It shall not be possible to remotely open any door from the central operating console". Older systems may not be in compliance with this regulation.
Regulations also require protection against failure: for the safety of the ship, a single electric failure in the power-operating or control system of a power-operated sliding watertight door shall not result in a closed door opening. Electric motors, circuits, indicators and warning signals are protected against the ingress of water, and loss of power supply will activate a sound and a visual alarm at the central operating panel.
A very important device on the central operating panel is the "master mode switch", which has two modes: "local control" and "doors closed" (also known as bridge/remote control). The "local control" mode will allow any door to be locally opened and closed after use, by the person passing through the doorway. However, if the switch is placed in the "doors closed" mode on the bridge, any of the doors which are open or being opened will be automatically closed by this action from the bridge. SOLAS Regulation 13.5.1 requires power-operated watertight doors to be capable of being closed simultaneously from the navigation bridge in no more than 60 seconds with the ship in the upright position. Whenever a door is closed remotely by power, there is to be an audible, distinct alarm at the door, sounding for at least five but no more than 10 seconds before the door begins to move and until the door is completely closed. As mentioned above, doors cannot be remotely opened from the bridge, but the "doors closed" mode will still allow a door to be opened locally, for the safety of an escaping person. However, the door will then automatically start to close upon release of the local control lever.
In earlier days there may have been an understanding among deck officers that the bridge should have overall control over the watertight doors, and to ensure that they were always closed, they kept the master mode switch in "doors closed", i.e., in bridge control. That is not so. SOLAS Regulation 13.7.8 states: "The "master mode" switch shall normally be in the "local control" mode. The "doors closed" mode shall only be used in an emergency or for testing purposes. Special consideration shall be given to the reliability of the "master mode" switch."
As for local control, each watertight door is to be able to be opened and closed by power from both sides of the door. With the ship in upright position, the closure time for the doors shall in no case be less than 20 seconds or more than 40. Control handles are to be provided at a minimum height of 1.6 metres above the floor and shall be so arranged as to enable persons passing through the doorway to hold both handles in the open position without setting the power-closing mechanism in operation accidentally. The direction of movement of the handles for opening and closing the doors shall be in the direction of the door movement and shall be clearly indicated.
Each door is also to be provided with an individual hand-operated mechanism, so the door in an emergency can be opened and closed manually at the door itself, from either side. In addition, it should be possible to close watertight doors in bulkheads of passenger ships with a hand-operated mechanism from an accessible position above the bulkhead deck. That location should also have clear indication that the doors are open or closed. Time necessary for the complete closure of the door by hand gear is not to exceed 90 seconds with the ship in upright position.
Periodical operation and inspection of watertight doors
Part B-4 of SOLAS Regulation 21 requires weekly drills for operating watertight doors in passenger ships, and if the voyage exceeds one week, also a complete drill before leaving port. It also requires that all doors in watertight bulkheads in use at sea be operated daily. The watertight doors and all mechanisms and indicators must be inspected at sea at least once a week. A record of all drills and inspections required by this regulation shall be entered in the log-book with an explicit record of any defects discovered.
Due to their importance, watertight doors should also be carefully examined by the surveyors at times of annual and renewal surveys of class, safety construction and loadline certificates.
Doors to be kept closed at sea
Part B-4 of SOLAS Regulation 22 "Prevention and control of water ingress, etc." requires all watertight doors to be kept closed at sea, with the following exceptions: to permit the passage of passengers and crew, or when work in the immediate vicinity of the door necessitates it being opened. The door must be immediately closed when the transit through it or the work is completed. Regulations are particularly strict for doors wider than 1.2 metres. Flag administrations may also permit certain doors to remain open during navigation if considered absolutely necessary, determined essential to the safe and efficient operation of the ship's machinery or to permit passengers unrestricted access throughout the passenger area, but "only after careful consideration of the impact on ship operations and survivability". Doors allowed to be open shall be clearly indicated in the ship's stability information and shall always be ready to be immediately closed.
Watertight doors may only be fitted in watertight bulkheads dividing cargo spaces if considered essential by the flag administration (SOLAS Regulation 13-1.4 for cargo ships and 13.9.1 for passenger ships), and shall be closed before the voyage commences and kept closed during navigation. They are not to be remotely controlled and are to be fitted with a device which prevents unauthorised opening. The time of opening such doors in port and of closing them before the ship leaves port shall be entered in the log book (Regulations 22.6 and 24.3).
Considering the impact of open watertight doors on passenger ships' operation and survivability, the IMO has, in reference to SOLAS Chapter II-1, Regulation 22.4, issued MSC.1/Circ.1380, "Guidance for watertight doors on passenger ships which may be opened during navigation". The guidelines start with a clear requirement that the number of doors is to be kept to a minimum: "Watertight subdivision is vital to ship stability and survivability to protect life, property and the marine environment in cases of hull damage after collision or grounding. The number of openings in watertight bulkheads on passenger ships is to be kept to a minimum in accordance with SOLAS Regulation II-1/13.1". Furthermore, concerning the importance of having watertight doors in closed position if a structural damage should occur to the ship, the guidelines say: "Failure to recognise the importance of watertight doors can have great impact on the watertight integrity of the ship and have catastrophic consequences".
The guidelines provide a procedure for floatability assessment of passenger ships, and divide watertight doors in categories A, B, C and D in accordance with when and if they may be kept open. In short, a type A door is a door that has been accepted to remain open during navigation, a type B door is a door that shall be closed, but may be left open for the time that personnel are working in its immediate vicinity. A type C door shall be closed, but may be opened to permit passage before being immediately closed again, and a type D door shall be closed before the voyage commences and remain closed during navigation.
The guidelines also contain a useful checklist designed for the use of flag states when determining if a door may be open during navigation. Operational instructions on board are to specify how doors are to be operated in accordance with the assigned category. The assigned category and meaning of each category should be clearly marked on both sides of each door or on the bulkhead adjacent to the door. The assigned category for each door is also to be indicated on the central operating panel on the navigation bridge.
Watertight doors and fire protection
SOLAS Chapter II-2 Part C deals with suppression of fire and Regulation 9 with how to contain a fire in the space of origin and how a vessel is to be subdivided by thermal and structural boundaries. Watertight doors to be fitted below the bulkhead deck do not need to be tested according to the Fire Test Procedures Code (IMO FP 46/5). The doors are therefore normally steel doors without insulation.
Gard is of the view that watertight doors in watertight steel bulkheads represent a certain weakness in case of fire, not just because they are not normally insulated, but because, if the door is not closed, smoke, poisonous gases and fire could go through the door to other areas of the ship. There have been cases of ships having a fire in the engine room and the crew being forced to leave the engine room by a watertight door, without closing it behind them.
Should a higher fire class than A-0 be required of a bulkhead below the bulkhead deck, such as A-15, A-30 or A-60, there is no requirement for the watertight door to be insulated. A separate fire door could be fitted in sequence with the watertight door to achieve a desired fire class, but that does not seem to be required.
Watertight doors of older designs meet steel to steel, and may not be absolutely watertight. Modern doors close by compression of a rubber seal, but there is no precise requirement for the rubber seal to withstand a fire. To have both a fire and water ingress in the engine room, for instance, may appear not to have been part of the risk considerations of the regulators.
Any comments on this article can be e-mailed to the Gard News Editorial Team.
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