The central bank or CO2 flooding system is the most commonly used fixed fire fighting system onboard a vessel. Its similar equivalent used in shore-based industries or institutions is known as the CO2 fire suppression system. That is basically the same thing but with lesser CO2 bottles/tanks.
This system of suppressing fire with the help of flooding the compartment with CO2 came in quite handy in event of an uncontrolled fire in the engine room or cargo spaces. In this system bulk quantity of CO2 is released to protect ER, Cargo hold, purifier room, pump room, etc.
CO2 bottle/cylinders flood CO2 to space where there’s fire origin, CO2 from bottle is directed to common manifold than to the main valve, and then to distribution pipeline to nozzles.
1) CO2 is an effective fire suppressor agent which may be used in different classes of fire.
2) It has a high expansion rate which allows it to work fast.
3) CO2 density is 1.5 times higher than that of Air, so CO2 settles down and displace air.
4) It can be easily liquefied and bottled.
5) 20 % to 30% of CO2 concentration is sufficient to extinguish the fire.
7) Non-Conductor of electricity
8) No residue is left after application
9) No deterioration with age.
This CO2 Flooding system is called a total flooding system because once it is initiated, all CO2 bottle connected to this system is discharged at once. Therefore it may also be termed as “one-shot system”!
This system is provided for Main engine or auxiliary engines whose total power is 746kW or more
NOTE: The first and the foremost thing before using this system is to ensure that the Engine room or Pump room is evacuated and all people are accounted for in muster.
Working of CO2 Flooding System
1) In case of fire, if Fire team is unable to extinguish the fire, this message is given to the Master/Captain of the vessel, and the captain decide whether to release CO2 or not, and Chief engineer is the one who is appointed to initiate the release.
2) Ensure that space to be flooded is evacuated of the personnel and is sealed off.
3) All Machinery should be stopped.
4) When the release cabinet box is opened, an alarm sound in the engine room, ventilation stop, all the damper get closed.
- A key to the box shall be in a break-glass-type enclosure conspicuously located adjacent to the box
5) First pull the starting bottle handle, second, pull the master valve handle.
6) After 60 to 90 seconds, the release of CO2 will get initiated in a designated place. This time delay is provided for a reason:
- To provide sufficient time for personnel to escape, even after both the valves in the release cabinet are operated.
- If CO2 is released in the mainline before the opening of the master valve, CO2 pressure will act on the valve and prevent the opening of the master valve, to open the valve great effort will be required.
Means shall be provided for automatically giving audible warning of the release offire-extinguishing medium into any Ro-Ro spaces and other spaces in which personnel normallywork or to which they have access. The pre-discharge alarm shall be automatically activated(e.g., by the opening of the release cabinet door). The alarm shall operate for the length of timeneeded to evacuate the space, but in no case less than 20 s before the medium is released.Conventional cargo spaces and small spaces (such as compressor rooms, paint lockers, etc.) with only a local release need not be provided with such an alarm. [Source: IMO.org ]
Time Delay Unit :
- Electronic Time Delay: This type of delay timer consists of a Pressure Switch, Timer, power supply of 220V, and a solenoid valve.there have been instances where the carbon dioxide system activated independent of the control panel, and no electronic time delay or audible alarm were activated. This exposed the enclosure occupants to a potentially life-threatening concentration of CO2.
- Pneumatic Time Delay: This system is considered more fool-proof.
as no carbon dioxide can be discharged without the alarm activating and sufficient time delay for occupants to evacuate the enclosure.
1) Pressure testing is done annually
2) Cables are made up of phosphorus bronze which is rust/dustproof and does not require extensive maintenance, but we check and apply grease to wire and pulley.
3) CO2 line has to blow through annually with compressed air.
4) Check the bottles, weighing of a bottle every 4 months.
5) Use Radioisotopes
6)Check the entire pipeline, lines are made up of mild steel, sometime CO2 line will be Galvanized (Zinc Coated)
1) Ensure that fans are shut off.
2) Ensure that skylight is closed
3) The funnel flap should be shut.
4) To make sure that, all fuel handling machine is off. In a modern vessel, it can be done from fire control station.
5) Ensure all personnel are evacuated
6) Normal bottle pressure is about 52Bar (Varies with ambient temperature), CO2 bottle room temperature should not exceed 55°C, Bursting disk rupture at 117Bar (At 63°C)
What if there’s a fire in the CO2 battery room or starting bottles room?
CO2 battery bottles have seals that act as Self Rupturing of bursting disk when there’s a fire in the CO2 room. In starting bottle pipeline pressure transducer detect the leakage and give the alarm of leakage, the relief valve is provided to avoid pressurization of the pipeline and to release the CO2 in CO2 room and extinguish the fire.
Testing of CO2 pipeline and arrangement.
1) The master lines end at Nozzles that are situated at deck head, is threaded.
2) Remove nozzle head, put plug-in nozzle, start the pressure testing.
3) See the pressure gauge and when it is at 7BAr, close the valve, and check whether there’s a drop, identify the leakage if any.
4) This testing should be carried out annually, but as it is time-consuming, the risk is taken and is done at every dry dock.
Test B) Bottles are of solid drawn manganese steel hydraulically tested at 228Bar
Test C) Recharging of the bottle is necessary if more than 10% of weight loss
- Quantity of CO2 is calculated from the gross volume of the largest machinery compartment or cargo-space.
- 85% of total CO2 should be released within 2 minutes of initiation of the system
- Pilot line and safety valves are similar to Master valve and mainline
CO2 Flooding System for Cargo Hold
This co2 flooding system is sometimes called as Semi-Controlled System because in this system we can control how many CO2 bottles to release (in contrary to Total CO2 flooding, where all CO2 bottles are released at once) but we cannot control how much volume is to be released ( as in Bulk CO2 Fully-controlled System )
This system is a combined system, having detection alarm and CO2 flooding system for the cargo hold.
- The air is drawn continuously by suction/extraction fan from cargo hold by creating a vacuum, which is positioned on top of the detection box.
- The air sample is delivered to helm-men (Steering Wheel) by diverting valves
- When an actual fire take place in cargo-hold, the smoke starts to rise through 3 Way Valve -> Glass Tube -> Propeller -> Smoke detector -> Suction Fan -> Diverting Valve
- When the smoke rises, initially diverting the valve direct it toward helmsman’s face, its smell is perceived by the helmsman, then he directs the smoke outside the wheelhouse otherwise wheelhouse will fill with smoke.
- Electronic smoke detection can trigger audio/visual alarm, it’s useful in case when the wheelhouse is unmanned in port, the outbreak of cargo-hold fire can be detected.
- Smoke detector (Photosensitive) become more effective during the port stay (unmanned period)
- Detecting cabinet has changed over valve at the bottom part, to take in the sample air, and to release CO2 to the given cargo-hold.
The Chimney is labeled and the middle part of the cabinet is brightly lit, the passage of smoke can easily be seen in the glass tube, and from reading the label of the chimney above the glass tube origin of the smoke can be known.
Who Operates this system.
Once the Cargo-hold with fire is indicated, the Chief Officer operates the change-over valve and all the other 5 Valves that are connected in the same hold.
Factor to decide how many cylinders of CO2 to be release
- Type of Cargo (Nature of Cargo)
- Cargo-hold Permeability
- The distance and ETA to reach the salvage port
- Interval of topping up
- Type of Cargo (Nature of Cargo): What type is cargo is loaded, is it highly or moderately flammable.
- Cargo-hold Permeability: It is cargo packing density, that is, are cargo is tightly packed or space is between different cargo.
- The distance and ETA to reach the salvage port: Whatever loss has occurred should always be calculated at the Salvage port and never at the sea.
- Interval of topping up: Since the hatch-covers gasket is watertight and not airtight, the topping up the interval of CO2 is decided to maintain a non-flammable zone with a cargo hold.
1) Once the cargo is empty and another is arriving, in the time between the check is taken out.
2) Smoke detection should be actually tested by spray can, disable the audio alarm, and see it with the blinking of LED on alarm.
3) Weight bottle regularly every 3 months.
4) Radio Isotope Testing: rub the transmitter along the cylinder along the length of the cylinder to know the quantity of CO2 within the cylinder.
Bulk CO2 Flooding System (Fully Controlled)
These systems are mostly observed in RO-RO vessels.
This is called a Fully controlled system because in this system we can control the volume of CO2 to be released.
1) When the compartment is identified which has an origin of the fire and spread of fire by fire and smoke detector.
2) The section valve of that compartment is opened
3) Then the Main Discharge Valve of the line is opened for a specific period, this specific period depends upon the size of the compartment.
4) When a sufficient volume of CO2 has been released, the main discharge valve is shut.
About the system :
- The Bulk CO2 cylinder has Insulating Layer and Metallic Cladding (protect the insulating layer.).
- It is an independent system, having two independent Compressors, expansion valve and Evaporator, in event of failure of one, another starts automatically.
- Pressure Switch gets its pressure from the Bulk CO2 cylinder. The pressure is directly proportional to temperature (Charles Law)
- When in ideal condition, when desired pressure is achieved, the compressor stops.
- The heater is used when the ship enters into the colder region, where the temperature is drastically low, we use a heating coil to heat the CO2 to -20C
- The isolating valve is used for repairing Pressure Switch
- Pressure Transducer sense pressure and trigger high and low-level alarm
- Level Transducer detect the level within the cylinder
- Change over valve is provided before two relief valve because in the case of crystallization of one relief valve other can be operational.
- There is High Pressure (H.P) and Low Pressure (L.P), H.P is set to about 27Bar and release CO2 within the CO2 room to extinguish any fire that occurs inside CO2 room, whereas L.P is set to 24 to 25Bar.
Topping Up of Bulk CO2 cylinder
When in port, ensuring that all the valves are closed.
Attach the incoming CO2 connection to CO2 liquid filling manifold.
Attach the Vapour recovery line back to the source of CO2.
Open Liquid filling line.
Within Bulk CO2 Cylinder
Temperature = 20°C
Pressure = 21 Bar
- High Level: When CO2 is 98% volume of a cylinder.
- High Pressure: Sound at 21.7 Bar.
- Low pressure: 13.8 Bar.
- Low Level: When CO2 reduced 5% of the total content.
- Opening of Section Valve.
- Leakage of Main Discharge Valve: Sound in case of leakage or accidental release.
- Control cabinet door switch alarm: Sound in all cargo-hold.
- Bulk carbon dioxide and its instruments are to be checked daily. For this purpose, a separate Log-book is maintained.
- The content gauge is to be checked for any leakage. Remote indication to be checked daily. Stand-by should be checked weekly.
- The rubber balloon connected to the relief valve is to be checked daily. The balloon is connected to H.P and L.P.
- A periodic survey of fridge compressor is done by a class surveyor every five years.
- Every ten years an internal inspection is carried out through manhole. This will be done only on dry-dock.
Advantage and Disadvantage Of Bulk CO2 Flooding System over the Cylinder carbon dioxide system.
- Full control on release of CO2, so we have CO2 for future use.
- Reduce filling costs.
- Simple filling arrangement.
- 50% (approximately) saving in weight, because in place of a battery of CO2 bottle, a container is used.
- It requires less space and is compact.
- The initial cost is high, two separate units of the compressor, condenser, expansion valve, and evaporator.
- More maintenance is required.
- It is less reliable, in case of black-out (when an emergency is also not working), bulk CO2 will go waste. In-cylinder CO2 nothing as such will impair it.
- Require power supply for maintaining the system.
- The detection system is not built-in.
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