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Isolating air supply to machinery space fires and use of Fire main

Fire protection on ships is provided by detection and fire-fighting equipment together with structural features which are intended to contain an outbreak of fire and the employment when required of non-combustible materials to prevent its spread.



Air supply

An outbreak of fire requires a source of ignition, the presence of combustible material and ample oxygen. Of the three factors, oxygen is provided in large quantities in machinery spaces, accommodation, dry cargo holds and tanker pumprooms by ventilation fans. Air supply trunkings are not only a source for a supply of oxygen to feed the fire but also have potential for carrying smoke from one area to another.

Emergency stops must be fitted so that ventilation fans can be stopped from a position external to the space served. Trunkings are provided with flaps which can be used to isolate various areas as necessary. Provision should be made so that all openings which could admit air can be closed off from a safe position external to the space or from the deck.

Fire main

Whilst the various types of portable extinguishers form the front line of attack against a fire detected in its early stages, the fire main or one of the other fixed fire-fighting installations is used if a fire becomes established. The fire main extends to the full length of the ship and from the machinery spaces to the highest levels. Hydrants served by the main, are situated so that with suitable hoses any area on the ship can be reached.

Water is the chief fire fighting medium on a ship and the fire main is the basic installation for fighting fires. The system shown for the cargo ship (Figure below) has two independently powered pumps which are also used for general service and ballast. These pumps supply engine room hydrants and the deck main through the screw down isolating valve which must be accessible from outside of the machinery space. The latter is required to prevent loss of water through damaged pipework in the engine room if, to maintain the deck supply, the emergency fire pump has to be used.

A sea water supply system to fire hydrants is fitted to every ship (Figure 13.8). Several pumps in the engine room will be arranged to supply the system, their number and capacity being dictated by legislation (Department of Transport for UK registered vessels). An emergency fire pump will also be located remote from the machinery space and with independent means of power.

A system of hydrant outlets, each with an isolating valve, is located around the ship, and hoses with appropriate snap-in connectors are strategically located together with nozzles. These nozzles are usually of the jet/spray type providing either type of discharge as required. AH the working areas of the ship are thus covered, and a constant supply of sea water can be brought to bear at any point to fight a fire.

While sea water is best used as a cooling agent in fighting Class A fires it is possible, if all else fails, to use it to fight Class B fires. The jet/spray nozzle would be adjusted to provide a fine water spray which could be played over the fire to cool it without spreading.




International ship - shore connections

An international shore connection is always carried on board ship. This is a standard size flange which is fitted with a coupling suitable for the ship's hoses. The flange is slotted in order to fit any shore-side fire main and enable water to be brought on board a ship lying alongside.

International Ship-Shore Connection must be attached to a convenient hydrant when alongside to enable local fire brigades to attach their appliances. A clear sign is to be displayed indicating the location. The securing bolts are to be kept free and well greased. When stowed away, it is to be kept in a dry location away from the elements.




Cargo ship fire main
Fig: Cargo ship fire main




Fixed installations

A variety of different fixed fire fighting installations exist, some of which are specifically designed for certain types of ship. A selection of the more general installations will now be outlined.

Types of portable fire extinguisher

There are four principal types of portable extinguisher usually found on board ship. These are the soda-acid, foam, dry powder and carbon dioxide extinguishers. Details as below :
  1. Soda acid portable fire extinguisher
  2. The container of this extinguisher holds a sodium bicarbonate solution. The screw-on cap contains a plunger mechanism covered by a safety guard.

  3. Foam type portable fire extinguisher
  4. The main container is filled with sodium bicarbonate solution and a long inner polythene container is filled with aluminium sulphate

  5. Dry powder fire extinguishers
  6. The outer container contains sodium bicarbonate powder. A capsule of carbon dioxide gas is located beneath a plunger mechanism in the central cap

  7. CO2 portable fire extinguisher
  8. A very strong container is used to store liquid carbon dioxide under pressure




Fixed fire extinguishing installations

A variety of different fixed fire fighting installations exist, some of which are specifically designed for certain types of ship. A selection of the more general installations will now be outlined.
  1. Fire main system for cargo ships

  2. An outbreak of fire requires a source of ignition, the presence of combustible material and ample oxygen. Of the three factors, oxygen is provided in large quantities in machinery spaces, accommodation, dry cargo holds and tanker pumprooms by ventilation fans. Air supply trunkings are not only a source for a supply of oxygen to feed the fire but also have potential for carrying smoke from one area to another....

  3. Automatic water spray & water mist system for machinery protected area

  4. The automatic spray or sprinker system provides a network of sprinkler heads throughout the protected spaces. This system may be used in accommodation areas, and in machinery spaces with certain variations in the equipment used and the method of operation. ....

  5. Automatic foam induction system for machinery space fire

  6. Foam spreading systems are designed to suit the particular ship's requirements with regard to quantity of foam, areas to be protected, etc. Mechanical foam is the usual substance used, being produced by mixing foam making liquid with large quantities of water. Violent agitation of the mixture in air creates air bubbles in the foam. ...

  7. CO2 fire extinguishing installations for machinery spaces

  8. Fire extinguishing installations employing CO 2 stored under pressure at ambient temperature are extensively used to protect ships' cargo compartments, boiler rooms and machinery spaces. When released the CO 2 is distributed throughout the compartment, so diminishing the relative oxygen content and rendering the atmosphere inert....

  9. Inert gas systems, inert gas generator

  10. Inert gases are those which do not support combustion and are largely nitrogen and carbon dioxide. Large quantities suitable for fire extinguishing can be obtained by burning fuel in carefully measured amounts or by cleaning the exhaust gases from a boiler. ....

  11. Fire fighting Halon system

  12. A Halon storage system would be very similar to one using carbon dioxide except that fewer cylinders would be required. The liquefied Halon is usually pressurised in the cylinders with nitrogen in order to increase the speed of discharge. ....



Other important fire & safety equipments


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