CO2 Flooding System Explained

 

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Requirements of CO2 Room:

In CO2 flooding system, carbon dioxide bottles are placed in a separate room. The requirements for location, accessibility, use and ventilation of CO2 storage spaces as per IMO are:

1. Spaces for storage of cylinders or tanks for extinguishing gas should not be used for other purposes.
2. These spaces should not be located in front of the forward collision bulkhead.
3. Access to these spaces should be possible from the open deck.
4. Spaces situated below the deck should be directly accessible by a stairway or ladder from the open deck.
5. The space should be located no more than one deck below the open deck.
6. Spaces where entrance from the open deck is not provided or which are located below deck are to be fitted with mechanical ventilation.
7. The exhaust duct (suction) should be lead to the bottom of the space.
8. Such spaces should be ventilated with at least 6 air changes per hour.

CO₂ room safety arrangement:

1. Exhaust fan, and suction duct is provided at the bottom of the room. Any accumulated CO₂ from leakage at the bottom can be exhausted to atmosphere.
2. Cable operated Safety Valve is fitted on Pilot Cylinder discharge line.It prevents accidental discharge of CO₂ from Quick Release Cylinders due to action of leakage gas from Pilot Cylinder.
3. Relief Valves are fitted on each discharge line from cylinders so that leakage gas can safely dispose to atmosphere.
4. Check Valve is fitted in connection pipe between each cylinder discharge valve and manifold, so that leakage of one cylinder cannot effect other cylinder.
5. Each bottle has a combined Bursting Disc, which will rupture spontaneously at a pressure of 177 bar at 63΄C.
6. Pressure Gauge and pressure Alarm in the manifold.

Maintenance of CO₂ flooding system:

1. Weekly inspection for alarm system.
2. Bottles should be weighed yearly; level checked by ultrasonic or radio active isotope detector. Level reference mark should be provided. If 10% loss of weight, recharge them.
3. All the pulley, wire, rope and toggle must be free from dirt, scales and well lubricated.
4. CO₂ branch pipe and discharge nozzle should be cleared with compress air at two year interval.
5. Bottles should not be exposed to temperature of 60΄C.

Weighing of CO₂ bottle:

1. Bottles should be weighed yearly by special weighing device designed for this purpose.
2. It has a reference mark to determine 10% loss of weight.

CO₂ Quantity Calculation:  (by Regulation):

1. For cargo space, CO₂ quantity shall be sufficient to give a minimum volume of free gas, equal to 30% of gross volume of largest cargo space so protected.
2. For machinery space, CO₂ quantity shall be sufficient to give a minimum volume of free gas, equal to 40% of gross volume of machinery space so protected excluding the casing.

So, if weight of CO₂ / bottle  = 45 kg / bottle and Free gas volume of CO₂ = 0.56 m³/ kg.     then, Required CO₂ bottles for cargo space   = (0.3 x Largest cargo space gross volume) / (0.56 X 45)

and

Required CO₂ bottles for machinery space  = ( 0.4  x  Machinery space gross volume) / (0.56 X 45)

As mentioned earlier CO2 flooding system floods the protected space under fire with carbon dioxide, which displaces air, thereby removing one leg fire triangle for the extinction of fire. CO2 flooding system consist of main CO2 bottles, common manifold, master valve or distribution valve and distribution pipe lines with nozzles as shown in the figure below. Click on the diagram to enlarge.

Main CO2 bottles contain carbon dioxide in liquid state with a pressure of 56 bar at 20 degree Celsius. Pressure of CO2 at 25 and 30 degree Celsius are 64 bar and 71 bar respectively. So it is important to keep the temperature of CO2 bottles low for limiting the pressure inside bottles.

Machinery Space (Engine Room) CO2 Flooding Procedure:

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1.  CO2 from the main bottle is released by a ‘CO2 release cabinet’ as shown in the figure. As soon as the release cabinet door is opened, a micro switch is activated. The micro switch will ensure the activation of CO2 warning alarms and ventilation shut off. 
2. CO2 release cabinet or release box consist of two pilot CO2 cylinders or bottles containing CO2 gas inside. The pressure of CO2 inside these pilot bottles is same as that of main CO2 bottles. Only quantity of gas is different. 
3. For releasing CO2 to the protected space, one of the pilot bottle valve is opened. Now CO2 reaches two valves marked 1 and 2. First valve 1 is to be opened. Then CO2 passes through a non return valve and opens pneumatically operated master valve. Now master valve is opened. 
4. Next, open valve 2 in the release cabinet, which supply CO2 to main CO2 bottle head assembly through a non return valve and ‘time delay unit’. (Function of the time delay unit is explained below.)
5.  Head assembly consist of a pressure operated cylinder valve. This pressure operated cylinder valve prevents CO2 from bottle coming to the common manifold. As CO2 reaches the head assembly from pilot bottle, pneumatic actuator in the head moves and opens the pressure operated cylinder valve. Then CO2 from main bottle escapes to the common manifold via non return valve as shown. 
6. Each of the main CO2 cylinder have a head assembly and non return valve. The pilot CO2 line is connected to all these heads. All the CO2 from the main bottles now release to common manifold. Since the master valve is already open before, CO2 from manifold is released to the protected space through distribution pipe lines and nozzles.

Machinery space minimum requirement:

1. Two nos. of fire hydrants with hoses, minimum.
2. 10 ft³ of sand and sawdust with scoops.
3. One fixed installation of CO₂ or foam or Halon.
4. Portable extinguishers of at least 2 nos. of 2 ½ gallon (11.37 litres) foam or CO₂, depending on BHP.
5. Semi-portable extinguishers of 45 kgs of CO₂.
6. Drip pans and trays for every F.O. and L.O. tanks.
7. Monitoring, detection and alarm system.
8. Emergency fire pump.
9. 2 nos: of main fire pumps.
10. International shore connection.
11. Inert gas system.

Cargo Hold CO2 Flooding System :

1. The release mechanism of CO2 system in cargo spaces is same as that of the machinery spaces. The only difference is that the cargo spaces have a different type of fire detection system.
2. For detection of fire in cargo hold, a sample of air is drawn from all the cargo holds by an extractor fan.
3. This sample of air is passed through a cabinet wherein a set of smoke sensitive sensors analyze the sample.
4. The sensors will detect any presence of smoke in the sample. As soon as the sensor detects smoke in the sample, it activates the CO2 alarm system of the ship.
5. A part of the sample is also discharged to the wheelhouse in order to cross-check the presence of smoke in the sample. This can be done by smelling the smoke. The sample is later vented to the air.
6. In order to check whether the extractor is extracting samples from the holds, a small indicator propeller is fitted, which ensures that the samples are taken.

Cargo hold fire fighting: by CO₂ flooding system:

1. Remote detector fitted at the bridge can detect concerned cargo space.
2. This operation must be done by master’s order.
3. After ensuring no person left in cargo space, seal off the cargo space [closing of ventilation fan, fire damper, hatch cover].
4. Before discharging, change 3-way valve to CO₂ discharge line so that connection to smoke detector is isolated.
5. Open the quick opening valve so that alarm will automatically initiated.
6. Manual operation procedure and amount of CO₂ bottle to be released is stated in CO₂ room.
7. By master’s order, release the correct amount to concerned cargo space.
8. Topping up procedure must be followed at port arrival.

Safety devices on CO2 flooding system

1. Master valve with alarm switch.
2. Relief valves at manifold.
3. Stop valve and pull handle are in lock release cabinet and alarm switch.
4. Safety bursting disc at each CO2 bottle.
5. Leakage detecting pressure switch on manifold.
6. Non return discharge valves after CO2 bottles.

Requirements of CO2 bottles:

1. All bottles stamped at 52 bar pressure.
2. Bursting disc fitted, operates at 177~ 193 bar at 63 °C
3. Store in temperature less than 55 °C
4. Recharge if 5 % loss.
5. Clamped against movement and vibration(by wooden plank).
6. Remote and manual operation possible.
7. Hydraulically tested to 228 bar.
8. Level tested (by radio active level indication).
9. if > 10 years internal and external examination required.

General inspections in CO2 room:

1. Check emergency light and all other lights.
2. Check exhaust fan / ventilation.
3. Check all bottles overall condition, clamps, valves etc.
4. Check operating wire condition.
5. Check CO2 alarms.
6. CO2 room key should be in position.
7. Check the operating instructions.
8. Inspection to be recorded in log book and Saturday safety routine book.

Survey on CO2 flooding system:

1. Check CO2 weight every 2 years.
2. Testing of cylinder at 228 bars.
3. Blow through the lines
4. General inspection on Instructions, Key, Emergency lights, Ventilation, Alarms etc.

Advantages:

1. Can permeate throughout the space.
2. After discharging, it leaves no residues and no damage to other parts.
3. No hazard for electrical equipment.

Disadvantages:

1. Only suitable for confined space, and needs total sealing of the space.
2. Fatal to life.
3. Re-ignition can occurs after fire is completely died out.
4. No cooling effects, only extinguished by smothering and inhibition.