COC ORAL EXAM PREPARATION (PART – 16): CO2 FLOODING SYSTEM

 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:

• Spaces for storage of cylinders or tanks for extinguishing gas should not be used for other purposes.
• These spaces should not be located in front of the forward collision bulkhead.
• Access to these spaces should be possible from the open deck.
• Spaces situated below the deck should be directly accessible by a stairway or ladder from the open deck.
• The space should be located no more than one deck below the open deck.
• Spaces where entrance from the open deck is not provided or which are located below deck are to be fitted with mechanical ventilation.
• The exhaust duct (suction) should be lead to the bottom of the space.
• 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):

• 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.
• 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)

Machinery Space (Engine Room) CO2 Flooding Procedure:

CO2 System operation in Machinery Spaces:
A Co2 system of machinery spaces consists of a bank of Co2 bottles that can be operated from a remote place located away from the machinery spaces. The system also consists of pilot Co2 cylinders which control the activation of the bank of Co2 bottles. The Pilot cylinders are contained in a control box and are normally kept disconnected. The system is connected to the pilot cylinders and the control box with the help of steel wires or flexible pipes. All these pipes are fitted with a quick action coupling.

• When the system is to be activated, the coupling in plugged into the corresponding socket. The valves of the pilot cylinders will be opened with the help of the levers in the main CO2 control system.
• The CO2 from the pilot cylinders will open the system’s main stop valve.
• The main stop valve has a piston which gets depressed due to the Co2 gas pressure and allows the pilot gas to flow to the bank of CO2 cylinders.
• This pilot gas operates the cylinders’ valves. All these valves have an actuator which gets operated by the pilot pressure.
• The detection of fire is done by various sensors installed in the machinery spaces.Though the opening of control box operates an alarm, the main decision for CO2 flooding is taken by the Chief engineer, after due consultation with the master of the ship.
• Before releasing Co2 into the fire affected space, it should be made sure that everybody is out of the place and total head should be counted.
• The place is fully enclosed i.e all skylights & ventilators are closed air-tight and pumpsumps supplying fuel oil should also be stopped in order to prevent re-ignition.
• Separate levers for each and every space are present inside the main controlling cabinet. The operating of a particular lever activates the pilot bottles, which helps in releasing the complete bank of bottles designated for that place.
• With the opening of the master valve, Co2 is flooded inside the fire affected space, which then smothers the fire with the help of blanket effect.
• Boundary cooling should be carried out.

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.

Machinery space fire fighting: by CO₂ flooding system:

1. CO₂ flooding to machinery space must be done by master’s order.
2. CO₂ must be released by competent engineer, CE.
3. When cabinet door is opened alarm will sound and all ER fans will be stopped.
4. Before releasing, all ER crew to be counted.
5. All openings must be shut [ventilator flaps, fire damper].
6. All fuel pumps and quick closing valves of fuel tanks and fuel transfer line must be shut from remote control position.
7. After opening the cabinet door, master valve must be opened first.
8. Pull the operating handle of pilot cylinders.
9. CO₂ , released from pilot cylinder, operate the gang release bar so that all CO₂ from quick release or total flooding cylinders will be released to machinery space.
10. By regulation, 85% of the capacity must be able to be released within 2 minutes.

Cargo Hold CO2 Flooding System :

• 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.
• For detection of fire in cargo hold, a sample of air is drawn from all the cargo holds by an extractor fan.
• This sample of air is passed through a cabinet wherein a set of smoke sensitive sensors analyze the sample.
• 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.
• 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.
• 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.