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Fire fighting equipment for machinery spaces - Automatic water spray system

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.

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.

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The accommodation areas are fitted with sprinkler heads which both detect and extinguish fires. The sprinkler head is closed by a quartzoid bulb which contains a liquid that expands considerably on heating (Figure ). When excessively heated the liquid expands, shatters the bulb and water will issue from the sprinkler head.

A deflector plate on the sprinkler head causes the water to spray out over a large area. The water is supplied initially from a tank pressurised by compressed air (Figure below). Once the tank pressure falls, as a sprinkler issues water, a salt water pump cuts in automatically to maintain the water supply as long as is necessary. The system is initially charged with fresh water to reduce corrosion effects.

Sprinkler head
Fig: Sprinkler head

The complete installation is divided into several sections, each containing about 150 to 200 sprinklers and having an alarm valve. When one or more sprinklers operate water flows through the section valve and sounds an alarm and also provides a visual display identifying the section containing the fire.

In the machinery space the sprinkler heads are known as 'sprayers' and have no quartzoid bulb. Also the section valves are manually operated to supply water to the sprayers (Figure above). The system is pressurised by compressed air with a salt water pump arranged to cut in automatically if the pressure drops. The accommodation and machinery space systems may be combined by a valve which is normally kept locked shut.

The system should be regularly checked by creating fault conditions at the various section control valves by opening a test valve, and checking for audible and visual alarms.

Automatic water spray system
Fig: Automatic water spray system

Water mist (Fog)

Water mist (fog) sprinklers are being used as an alternative to, the now banned, Halon fire suppression systems. The mist system delivers very small water particles, which are able to remain suspended in the air. The water particles are evaporated by the heat of the fire and the expanding vapour displaces oxygen. The combined cooling and oxygen starvation effects quickly extinguishes a fire. Less water is used than with sprinkler systems and the mist has proved effective against liquid fuel fires, making it suitable for use in machinery spaces.

Research is continuing, in particular as to the effectiveness of mist in a large machinery space. Water mist is accepted as a fire extinguishing agent, with respect to SOLAS fire protection requirements.

Sprinkler Piping requirement

Small-bore pipes kept permanently charged with freshwater at about 10 bar pressure. A sprinkler system is arranged to release automatically at temperatures of about 70C, so the system can both detect and extinguish a fire. The system uses saltwater after the fresh. After use, it is flushed with freshwater to minimise corrosion. Some systems operate at higher pressures.

Water spray systems

Usually small-bore piping, which is dry when not in use. A water spray system is operated manually and looks similar to a sprinkler system.

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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