Probability of accidents caused due to fire is very high on ships, mainly because of high quantity of fuel oils and inflammable cargo that they carry. In case of a small intensity fire on ship, portable fire extinguishers or other handy means of extinguishing fire can be used. But in case, the intensity of fire is high or it is humanly impossible to control the fire, Co2 fire extinguishing system is used.
CO2 Fire Extinguishing System
Due to its physical and chemical properties, Co2 is the most commonly used gas on-board ships in order to extinguish fire during accidents. Co2 is used in a number of ways, mainly depending on the intensity of fire.
If the intensity of fire is less, it can be extinguished by using a small CO2 extinguisher which are often portable. But incase the intensity of fire is high then a fixed fire fighting system with higher capability is used.
Arrangement Of CO2 system
A fixed type of Co2 fire fighting system includes a large no of CO2 bottles arranged together. This system is mainly used for large areas on ships, such as cargo holds or machinery spaces of engine room, where fighting fire gets difficult due to extended spaces and fire intensity. This system is also known as Total flooding system, for the spaces affected with fire are totally flooded with Co2 in order to quench the flames.
In this system, the cylinders are grouped together in banks, in totally separate rooms away from the machinery or cargo spaces. All the cylinders are joined together with the help of a common manifold. The outlet of each cylinder discharges through a connecting pipe into this common manifold. A non-return valve is provided to each of this connecting pipes so that incase any of the CO2 cylinder has to be replaced or recharged , it can be done so without the loss of pressure.
Why Only CO2?
CO2 gas mainly used for extinguishing fires because of the following properties:-
1. At normal temperature,CO2 remains in the gaseous state.Co2 is also 1.5 times denser than air.This heaviness helps in displacing the air by making Co2 act as a blanket to cuts off the supply of oxygen to the fire.
2. CO2 is easily available and can be liquefied and bottled smoothly. It is normally contained under a pressure of approx. 50 bars in cylinders made out of steel.
3. When the liquid CO2 is released on fire,it boils off rapidly as a gas into the atmosphere, taking away the heat from the surrounding atmosphere and cooling down the environment.
4. CO2 is a non-flammable gas .
Advantages of using CO2 Gas
1. It is a non corrosive gas.
2. It is available everywhere
3. It does not conduct electricity.
4. It does not leaves any kind of residue.
5. It is non-flammable.
Disadvantages Of Using CO2 Gas
1. CO2 is the most toxic gas when it comes to human health. It is a highly suffocating gas, whose concentration of even 9% in the breathing air would make a person unconscious within minutes.
2. Though it provides a perfect smothering effect, the condition does not last for a long time. In case of non-continuous supply of CO2, chances of re-ignition increases if air is re-admitted to the compartment too soon after the fire.
Marine Auxiliary Machinery, 7th Edition by McGeorge , 1995