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Soda-acid type of Portable fire extinguishers working principle

Fire fighting at sea may be considered in three distinct stages, detection—locating the fire; alarm—informing the rest of the ship; and control—bringing to bear the means of extinguishing the fire.

Soda-acid extinguisher
The container of this extinguisher holds a sodium bicarbonate solution. The screw-on cap contains a plunger mechanism covered by a safety guard. Below the plunger is a glass phial containing sulphuric acid (Figure ). When the plunger is struck the glass phial is broken and the acid and sodium bicarbonate mix.

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The resulting chemical reaction produces carbon dioxide gas which pressurises the space above the liquid forcing it out through the internal pipe to the nozzle. This extinguisher is used for Class A fires and will be found in accommodation areas.

Soda acid portable fire extinguisher
Fig:Soda acid portable fire extinguisher

Maintenance and testing

All portable extinguishers are pressure vessels and must therefore be regularly checked.

The dry powder extinguisher is tested to 35 bar once every four years. Most extinguishers should be tested by discharge over a period of one to five years, depending on the extinguisher type,

Where practicable the operating mechanisms of portable extinguishers should be examined every three months. Any plunger should be checked for free movement, vent holes should be clear and cap threads lightly greased. Most extinguishers with screw-on caps have a number of holes in the threaded region. These are provided to release pressure before the cap is taken off: they should be checked to be clear.

The type, number and locations of portable and semi-portable extinguishers are supplied to cargo vessels according to SOLAS, Flag and Classification requirements. All fire fighting equipment must be in a constant state of readiness and be regularly and properly maintained. Any valves in these systems are to be operated and proved free every month.

Any defects with the equipment are to be reported to the Company immediately and rectified on an urgent basis. It is essential that when fire-fighting equipment is landed ashore for service or maintenance, sufficient quantities remain onboard to cope with an emergency situation. If required, equipment may be hired as a temporary replacement for the ship’s own equipment.

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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