Fire Fighting Equipment

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ref: introduction marine engineering

Fire fighting equipment

Portable extinguishers

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.

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.  When the plunger is struck the glass phial is broken and the acid and sodium bicarbonate mix. 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.

Foam extinguisher—chemical

The main container is filled with sodium bicarbonate solution and a long inner polythene container is filled with aluminium sulphate . The inner container is sealed by a cap held in place by a plunger. When the plunger is unlocked by turning it, the cap is released.The extinguisher is then inverted for the two liquids to mix. Carbon
dioxide is produced by the reaction which pressurises the container andforces out the foam.

Foam extinguisher—mechanical

The outer container in this case is filled with water. The central container holds a carbon dioxide charge and a foam solution . A plunger mechanism with a safety guard is located above the central container. When the plunger is depressed the carbon dioxide is released and the foam solution and water mix. They are then forced out through a special nozzle which creates the mechanical foam. This extinguisher has an internal pipe and is operated upright. Foam extinguishers are used on Class B fires and will be located in the vicinity of flammable liquids.
A very strong container is used to store liquid carbon dioxide under pressure . A central tube provides the outlet passage for the carbon dioxide which is released either by a plunger bursting a disc or a valve operated by a trigger. The liquid changes to a gas as it leaves the extinguisher and passes through a swivel pipe or hose to a discharge horn. Carbon dioxide extinguishers are mainly used on Class B and C fires and will be found in the machinery space, particularly near electrical equipment. The carbon dioxide extinguisher is not permitted in the accommodation since, in a confined space, it could be lethal.

Dry powder extinguishers

The outer container contains sodium bicarbonate powder. A capsule of carbon dioxide gas is located beneath a plunger mechanism in the central cap. On depressing the plunger the carbon dioxide gas forces the powder up a discharge tube and out of the discharge nozzle. The dry powder extinguisher can be used on all classes of fire but it has no cooling effect. It is usually located near electrical equipment in the machinery space and elsewhere on the ship.

Maintenance and testing

All portable extinguishers are pressure vessels and must therefore be regularly checked. The soda-acid and foam extinguisher containers are initially tested to 25 bar for five minutes and thereafter at four-yearly intervals to 20 bar.
The carbon dioxide extinguisher is tested to 207 bar initially every 10 years and after two such tests, every five years. 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, e.g. soda-acid and dry powder types 20% discharged'per year, foam types 50% discharged per year. Carbon dioxide extinguishers should be weighed every six months to check' for leakage. 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.