Understanding the CO2 flooding system

The CO2 flooding system is used to extinguish the fire in the protected space. here we use the protected space as an engine room, let's consider the engine room is going to be flooded with CO2, we can see lots of nozzles distributed all over the engine room, we can also see CO2 sounding alarms. we know there will visible and audible alarms to indicate that the CO2 is flooding inside the engine room. 

we have a CO2 room which is used to store the CO2 bottles. CO2 bottles totally depend on the gross volume of the engine room.

 

Before operation:

we have the control station or the valve release cabinet or control cabinet, so in order to flood co2 inside the engine room as a matter of fact the mustering should be done in the muster station headcount, order from the master and then with all confirmation with respect to company policy the master will give orders to the chief engineer to release the co2 and it is the chief engineer who has to release the co2 into the engine room and let's see what are the components inside the valve control station.

 

Location:

This control station can be located at different places but definitely outside the space to be protected. Here the protected space is considered to be the engine room. so the CO2 control station should be definitely outside the engine room otherwise working personal can't operate in the event of a fire inside the engine room. so we need to have a proper location of the control station to operate the system. In the ship, we have basic places where the control stations are generally located, one at the fire control station and other is the CO2 room itself and the third is just outside the engine room just at the entrance of the engine room.

Operation:

The release cabinet has pilot cylinders and it is enclosed inside a cabinet which as a door, once the doors open it gives audible and visual alarms and also it might trips ventilation fans and stop some fuel pumps it varies depending upon the ship.

But usually, it must give a definitely audible and visual alarm and which stops the ventilation fans, so we have two bottles out of which we use always use only one bottle and other is considered to be a spare. we are not going to use both the bottles so there is a valve over here and we need to open this and then there are two valves. one valve follows the green line goes and opens the main CO2 bottle valve mechanism. the other one if you follow the blue line, goes and opens the main distribution valve which is also inside the co2 room. so we open this valve the CO2 from the bottle comes and stands over here. 

As the chief engineer opens both the valves simultaneously, the green line CO2 goes through the time delay unit. The time delay unit produces a time delay of 20 to 30 seconds depending upon the system or the manufacturer and it's not present in all kind of ships. so it's not mandatory, it's just optional and the blue line goes to the main distribution valve for the engine room. so the time delay unit can be either electrical or a simple empty bottle which creates the time delay of 32 to 30 seconds just the time needed to fill up the bottle. 

The reason empty bottle kept is the CO2 from the pilot bottle takes time to fill up the empty bottle thus this how the time delay is created and electronically we have a solenoid valve mechanism which after let's say 20 second time delay it opens a solenoid and thus the CO2 goes and opens the main cylinder unit.

So as the chief engineer opens the release cabinet, the CO2 opens the main distribution valve which also has a limit switch that gives an indication that the main distribution valve is opened and after the time delay the main CO2 bottles corresponding to the engine room has also been opened, CO2 passes through the return value and each cylinder unit having a non-return valve, the CO2 released passes through the non-return valve reaches the main manifold and through the distribution valve and goes to the engine room through and gets distributed at the various nozzles to various platforms.

So as we all know there is a  requirement that 85% of the CO2 has to be released within 2 minutes of operation. so that the requirement.

So all the pipings, nozzles and diameter everything has been calculated so that the requirement has been met.

Now let's see on the main manifold we have a blank, we definitely have to have a blank over here so that for any maintenance purposes we can isolate the CO2 bottle section, we can blank it and then carry out maintenance on this area and we have valve over here through which you can connect air, either from the engine room or from the shore depending whether we are in dry dock or not and on the manifold, you have a pressure gauge indicating whether the line is pressurized or not and one of the main components of the manifold is a relief valve.

let's say, CO2 is released and for some reason, the main manifold distribution valve is not open. so in order to protect the line against another damage and to avoid the escape of CO2 from the relief valve to the atmosphere, the modern ships have a pressure switch over here. this pressure switch whenever there is a small leak or pressure in the line it detects pressure and gives an alarm might be either the CO2 leak alarm or the CO2 release alarm depending upon classification. The pressure switch can be either calibrated say pressure 1 to 10 bar as peak alarm and after 10 bar release alarm depends on the automation system of a ship and after that, we have the distribution valve which is operated through the piston and this piston push up the valve, opens up and then the CO2 goes to the engine room.

let's concentrate on the actual system which is present on board ship, we would consider the protected space as engine room which was isolated and at the protected space entrance we have the valve control station, so we can operate release the CO2 just outside the engine and in the conventional way you have the valve control station in the co2 and what are the five control station should so from three places you have a valve control station in the CO2 room and one at the fire control station. so from three places, you can flood CO2 inside the engine room.

The fire control station or valve control section: we have a key inside the break-glass type which is sealed, take the key by breaking the glass and open the cabinet by using that key. once we open the cabinet there will be a CO2 release alarm and the vent fans will stop.

Then we need to open the valve of one bottle in the cabinet, we will get a pressure indication on the pressure gauge.

The chief engineer will come to operate the main distribution valve and main CO2 bottles valve after confirming the vent fans have stopped, the quick-closing valve closed and the dampers are shut down.

So after these two valves are being operated, the first valve line (green line) will go and opens the main distribution valve to the engine room and you have a check valve or non-return valve over here so the gas from the pilot cylinder will only flow one way, it can't move reverse way and it cannot also go to the other valve control stations, we have a non-return valve over here so it opens the main distribution valve.

Similarly, the other valve line (blue line) goes through a check valve or non-return valve through a time delay unit to open the main CO2 bottles in the CO2 room and as the CO2 is released, goes through the main distribution line (that is open now) and then enters the engine room space through nozzles and gets flooded CO2 gas.

Now you have a similar arrangement in the CO2 room and also at the engine room entrance. Remember when you are operating from the engine room entrance ( if emergency stop arrangement quick closing valves, vents fans etc. is not there) somebody has to go to a fire station or emergency station, from where you have to shut the quick closing valve and the stop dampers, blowers, pumps. etc.