Central bank or CO2 flooding system are most commonly used fixed fire fighting system on-board a vessel. 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 the space where there’s fire origin, CO2 from bottle is directed to common manifold then to main valve and then to distribution pipe line to nozzles.
1) CO2 is an effective fire suppressor agent which may be used in different Classes of fire.
2) It has high expansion rate which allow it to work fast.
3) CO2 density is 1.5 times higher than that of Air, so CO2 settle down and displace air.
4) It can be easily liquefied and bottled.
5) 20 % to 30% of CO2 concentration is sufficient to extinguish fire.
7) Non-Conductor of electricity
8) No residue is left after application
9) No deterioration with age.
This CO2 Flooding system is called total flooding system because once it is initiated, all CO2 bottle connected to this system is discharged at once. Therefore is 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 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 captain decide weather 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 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 second, the release of CO2 will get initiated in designated place. This time delay is provided for a reasons :
- To provide sufficient time for personnel to escape, even after both the valves in release cabinet is operated.
- If CO2 is released in the main line before opening of master valve, CO2 pressure will act on the valve and prevent opening of 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 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.) withonly 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 consist of a Pressure switch, Timer, power supply of 220V and a solenoid valve.there have been instances where 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 are rust/dust proof and does not require extensive maintenance, but we check and apply grease to wire and pulley.
3) CO2 line has to be blow through annually with compressed air.
4) Check the bottles, weighing of bottle every 4 months.
5) Use Radio isotopes
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) Funnel flap should be shut.
4) To make sure that, all fuel handling machine are off. In 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 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 CO2 room. In starting bottle pipeline pressure transducer detect the leakage and give the alarm of leakage, relief valve is provided to avoid pressurization of the pipeline and to release the CO2 in CO2 room and extinguish fire.
Testing of CO2 pipeline and arrangement.
1) The master lines end at Nozzles that are situated at deck head, is 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 weather there’s a drop, identify the leakage if any.
4) This testing should be carried out annually, but as it is time consuming, risk is taken and is done at every drydock.
Test B) Bottles are of solid drawn manganese steel hydraulically tested at 228Bar
Test C) Recharging of bottle is necessary if more than 10% of weight loss
- Quantity of CO2 is calculated from 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 main line
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 cargo hold.
- The air is drawn continuously by suction/extraction fan from cargo hold by creating vacuum, which is positioned on top of 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 start to rise through : 3 Way Valve -> Glass Tube -> Propeller -> Smoke detector -> Suction Fan -> Diverting Valve
- When smoke rise, initially diverting valve direct it toward helmsman face, its smell is perceived by helmsman, then he direct 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 wheelhouse is unmanned in port, the out break of cargo-hold fire can be detected.
- Smoke detector (Photo sensitive) become more effective during port stay (unmanned period)
- Detecting cabinet has change over valve at bottom part, to take in the sample air and to release CO2 to the given cargo-hold.
The Chimney are labelled 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 chimney above the glass tube origin of the smoke can be known.
Who Operate this system.
Once the Cargo-hold with fire is indicated, Chief Officer operate the change-over valve and all the other 5 Valves that are connected in same hold.
Factor to decide how many cylinder 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 lose has occurred should always calculated at the Salvage port and never at the sea.
- Interval of topping up : Since the hatch-covers gasket are watertight and not airtight, the topping up interval of CO2 is decided to maintain non-flammable zone with 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 audio alarm and see it with blinking of LED on alarm.
3) Weight bottle regularly after 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 (Fully Controlled System)
These system are mostly observed in RO-RO vessels.
This is called 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 origin of fire and spread of fire by fire and smoke detector.
2) The section valve of that compartment is opened
3) Then Main Discharge Valve of the line is opened for specific period, this specific period depend upon the size of the compartment.
4) When sufficient volume of CO2 has been released, main discharge valve is shut.
About the system :
- The Bulk CO2 cylinder has Insulating Layer and Metallic Cladding (protect the insulating layer.).
- It is independent system, having two independent Compressor, expansion valve and Evaporator, in event of failure of one, other start automatically.
- Pressure Switch get its pressure from Bulk CO2 cylinder. Pressure is directly proportional to temperature (Charles Law)
- When in ideal condition, when desired pressure is achieved, compressor stop.
- Heater is used when ship enter into colder region, where temperature is drastically low, we use heating coil to heat the CO2 to -20C
- Isolating valve is use for repairing Pressure Switch
- Pressure Transducer sense pressure and trigger hinh and low level alarm
- Level Transducer detect the level within the cylinder
- Change over valve is provided before two relief valve, because in 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 occured inside CO2 room, where as 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 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.
- Content gauge is to be checked for any leakage. Remote indication to be checked daily. Stand-by should be checked weekly.
- Rubber balloon connected on the relief valve is to be checked daily. Balloon is connected to H.P and L.P.
- Periodic survey of fridge compressor is done by 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 carbon dioxide system over Cylinder cabon dioxide system.
- Full control on release of CO2, so we have CO2 for future use.
- Reduce filling cost.
- Simple filling arrangement.
- 50% (approximately) saving in weight, because in place of battery of CO2 bottle, a container is used.
- Require less space and is compact.
- Initial cost is high, two separate unit of compressor, condenser, expansion valve and evaporator.
- More maintenance is required.
- It is less reliable, in case of black-out (when 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.
- Detection system is not built-in.