In your junior school, you might have been taught that you should not use water to douse a fire that has been caused by electricity and use sand instead. This is because the method of extinguishing fire varies with the source of its origin. Ships use different types of fire extinguishers to based on what was acting as the fuel for the fire.
Different areas of the ship have different portable fire extinguishers based on the potential source of fire in that area. These happen to be one of the most convenient and efficient methods of firefighting.
Fire extinguishers may be classified into the following types – class A, B, C, D and E. Fires arising from the burning of wood, glass fibre, upholstery and furnishing are taken care of by the class A type fire extinguisher. Fire caused by lubricating oils and fuels are doused using class B type fire extinguishers. Class C type fire extinguishers help in controlling fire caused by energized electrical equipment like motors, switches, wiring etc. Combustible materials like magnesium and aluminium need special handling too and are hence extinguished by the class D type extinguishers. Any of the aforementioned types of fire that also involves high voltage electricity is taken care of by the class E type fire extinguishers.
|International Organisation for Standardization (ISO Standard 3941)|
|Class A||Fires involving solid materials, usually of an organic nature
, in which combustion normally takes place with the formation
of glowing embers
|Class B||Fires involving liquids or liquefiable solids|
|Class C||Fires involving gases|
|Class D||Fires involving metals|
|Class F||Fires involving cooking oils|
There are basically five main types of fire extinguishers that are kept on the ship. They are:
- Soda Acid Extinguisher
- Water Extinguisher
- Foam Extinguisher – Chemical and Mechanical
- Carbon Dioxide Extinguisher
- Dry Powder Extinguisher
Types of Fire Extinguishers used on Ships
1) Soda Acid Extinguisher
The primary components of this extinguishers are Sodium bicarbonate (soda) and sulphuric acid. These two chemical components react to form carbon dioxide which is used to put out the fire. The system inside the extinguisher consists of a container. The sodium bicarbonate is filled in this and sulphuric acid is put in a small glass bottle that is put under a plunger mechanism. This, in turn, is protected by a safety glass. On the top, there is a screw and a cap.
The glass bottle breaks when the plunger is struck hard. This causes the sodium bicarbonate and the sulphuric acid to come in contact with each other and result in the desired chemical reaction. The carbon dioxide thus formed creates a pressure on the space above the liquid thus causing it to squirt out of the internal pipe of the nozzle.
However, the gas is known to produce toxic effects and hence the use of soda acid extinguishers on ships has been banned.
2) Water Extinguisher
Portable 9L water extinguishers are used to combat the A-class fire. Here the outer container is filled with water. The water is forced out of the opening with the help of CO2 which is put inside the inner container in a cartridge that helps create pressure.
To use the extinguisher you first need to safety pin/clip. On applying pressure to the plunger the CO2 cartridge ruptures and the water is forced out of the nozzle.
3) Foam Extinguisher
Foam extinguishers are of two types – mechanical and chemical. They are used to extinguish class B fires and are hence kept near flammable liquids.
Mechanical foam – It consists of two containers. The outer one is filled with water while the one in the centre houses carbon dioxide charge and foam solution. The plunger mechanism at the top of the central container releases carbon dioxide when depressed allowing the foam and water to form a mixture that comes out of the nozzle. The extinguisher is held in an upright position while using.
Chemical foam – This type of extinguisher has sodium bicarbonate and aluminium sulphate as its primary comments.
Just as in the previous case this too has a two containers. The main container stores sodium bicarbonate while the inner one is filled with aluminium sulphate. However, unlike last time this one is inverted while operating to let the two chemicals of the containers mix. This flow is controlled by a plunger which holds the cap on the inner container in place. The foam is forced out by the pressure created by the carbon dioxide that is formed from the chemical reaction.
It is worth noting that chemical foam extinguishers have been banned on ships.
4) Carbon Dioxide extinguisher
Mainly used for class B or C fires, this type of extinguishers are to be used in only open places because the gas can prove to be really poisonous otherwise. Hence they find their place mostly in machinery spaces.
The constituent of this type of extinguisher is quite evident from the name. The carbon dioxide is stored as a liquid under tremendous pressure and comes out through a central tube. A plunger controls the flow of the liquid carbon dioxide which as soon as it comes in contact with the normal air turns into gas.
5) Dry Powder Extinguisher
This is the most special of the lot because this class of extinguisher can combat any kind of fire. The primary constituent is sodium bicarbonate and they are kept near electrical equipment. Just as the other extinguishers this too uses carbon dioxide to create pressure that enables the container to push out the gas through the discharge nozzle.