Friday, September 20, 2013

CO2 Fixed Fire Fighting System: An Idiot's Guide!

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An Idiot's Guide to
CO2 Fixed Fire Fighting System

[Special Contribution by Gokul Rajaram from MEO Class IV Orals Group]

All about CO2 Systems: Requirements, System and Procedures!

Carbon Dioxide
Carbon dioxide is an effective fire suppression agent applicable to a wide range of fire hazards.  It has a high rate of expansion which allows it to work fast. When applied to a fire, CO2 provides a heavy blanket of gas that reduces the oxygen level to a point where combustion cannot occur. Since carbon dioxide is a gas, there is no clean-up associated with a system discharge which means minimal business interruption.

CO2 Critical Temp/Press
The critical temperature/pressure of a substance is thepress/temp at and above which vapor of the substance cannot be liquefied, no matter how much pressure is applied.
For CO2, Critical Temp= 31.2 deg C; Critical Pressure= 73 bar

Co2 System Requirements
  • Discharge Req:
  1. At Least 50% discharge @ 1 min.
  2. At Least 85% discharge @ 2 min.
  • Capacity Req:
  1. 30% of gross vol @ THE LARGEST PROTECTED cargo space
  2. 40% gross vol @ machinery space EXCLUDING CASINGS
  3. 35% gross vol for vessels GT < 20000 (WHEN CASINGS ARE INCLUDED)
  4. Total no of CO2 cylinders depend upon the highest gross vol out of points 1,2,3 in a particular ship
Major Other Requirements
  • Safety procedures against unauthorised use of the system
  • Machinery Space valve to be fitted with alarm (audio+visual) and blower trip
  • Alarm must trigger well before operation
  • Permanent piping arrangements
  • Distribution Manifold+ piping, pressure test @ 122 bar
  • Pipe D > 19mm
  • Cu and flex pipes allowed between cylinder outlet and Manifold
  • Pipes to Cargo Spaces, not to pass through E/R
  • Hydraulic Pressure Testing for bottles after 20 years from date of installation and thereafter every 5 years
  • Quantity of CO2 to check every 4 years which can be distributed as 25% of bottles annually, this must ensure checking of each bottle every 4 years
  • All Stop valves to check monthly to ensure their position and working
  • The installation must be checked monthly for leakages
  • All connection to cable operating system to inspect for tightness every 3 month
  • All control valves to inspect annually
  • Air blow through annually

CO2 Calculation Requirement

  • Quantity of CO2 shall be calculated at Density = 0.56 m3/kg
  • Mixing Ratio of CO2, 
  1. Gross vol of E/R including casing = 35%
  2. Gross vol of E/r excluding casing = 40%
  3. Gross vol of cargo holds = 30%
  • Quantity of CO2 = (gross vol x mixing ratio)/0.56
  • Required No of Cyl = (quantity of co2/45) [in case of 45kg cyl]
  • Refer to the example for CO2 calculation for better understanding
co2 requirement calculation with example
co2 calculation: sorry about poor picture quality


CO2 Precautions and Points to Remember


  • It is recommended that in the event of any fire breaking out onboard, including one that requires the fixed CO2 system to be activated, the nearest Coastguard to your position is informed as soon as practicable.
  • Carbon dioxide (CO2), a compound of carbon and oxygen, is a colourless gas with a slightly astringent smell causing coughing to occur when inhaled; at high concentrations it is acutely toxic. As it is about 50% heavier than air, it will form a blanket over a fire and smother it.
  • To obtain “total flooding” of an engine room, a CO2 concentration of about 35% by volume or more is required to be obtained within 2 minutes. This will reduce the oxygen content of the air in the space to less than 15% to extinguish the fire. At this CO2 concentration human life cannot be supported.
  • It is therefore essential that personnel leave the space as soon as the CO2 warning alarm sounds. CO2 should not be discharged into a space until all those within have left and a full head count has been taken.
  • Before a space is filled with CO2 it is essential that the compartment ventilation flaps are properly closed and sealed, ventilation fan emergency stops and all fuel and hydraulic oil remote quick closing valves are operated.
  • Masters, skippers and crew should be fully competent with the remote and local operation of the fixed CO2 fire extinguishing system for the isolation of fuel oil, hydraulic oil and ventilation systems from the space.
  • Typically, it takes about 15–20 seconds after release of CO2 before the concentration within the space reaches a dangerous level.
SAFETY PRECAUTION BEFORE CO2 RELEASE
  • Inform Bridge which inturn inform nearest Coast Guard
  • All personell evacuated and head count done
  • Ventilators & Fans Auto Stop upon opening the CO2 release cabinet
  • Dampers, Skylight & All Entry Doors Closed
  • M/E and other machinery stopped
  • All QCVs operated
  • All pumps stopped
  • Emergency Generator Run for using Emergency Fire Pump for boundry cooling (if required)
  • Fire mains Isolating Valve to be closed so that pressure is not lost by supplying water to deck line
SAFETY PRECAUTIONS AFTER CO2 RELEASE


  • It is strongly recommended that expert advice should be obtained from ashore before ventilation of the space or any attempt at re-entry is made. The nearest Coastguard to your position may be contacted who will assist in trying to obtain this advice. Unless specifically requested, this will not be interpreted by the Coastguard as a request for on-scene fire-fighting assistance.
  • Immediately after activation of the CO2 system checks should be carried out to ensure that the gas has been correctly released from the cylinders. This can be achieved by feeling the CO2 cylinders which should be cold to the touch and visually checking the individual cylinder release valves to ensure they are in the open position.
  • Crew should keep well clear of the ventilation flaps to prevent the inhalation of noxious gases.
  • Ventilation of the space should not be resumed until it has been definitely established that the fire has been extinguished. This is likely to take several hours
  • Entry into a space that has contained CO2 should only be attempted by trained personnel wearing breathing apparatus with safety lines attached and sufficient back-up immediately available should difficulties arise.
  • An attendant should be detailed to remain at the entrance to the space whilst it is occupied.
  • An agreed and tested system of communication should be established between any person entering the space and the attendant at the entrance.
  • Should an emergency occur to the personnel within the space, under no circumstances should the attendant enter the space before help has arrived and the situation has been evaluated to ensure the safety of those entering the space to undertake the rescue.
  • In the event that the ventilation system fails any personnel in the space should leave immediately.


CO2 Fixed Installation Explanation+Procedure 

[Unitor Example Used: All Rights Reserved to Unitor]

Unitor CO2 System is designed as total flooding system

co2 high pressure ffs line diagram
co2 ffs high pressure system


Unitor CO2 System consists of a high pressure cylinder bank with either manual or pressure operated cylinder top valves, with one or more pressured CO2 cylinders connected via a common manifold.
Wilhelmsen Technical Solutions has a type of pressure operated cylinder valve, which only requires a small quantity of gas to release the system and therefore it is fast operating and applicable to operate in big series. Automatically closes when evacuating the pilot gas.
The cylinder bank and unique manifold will be stored in a well-ventilated and insulated room, and the pressure operated valves are connected to the manifold using flexible high pressure hoses.
From the main manifold, CO2 is led through the distribution valves to the protected spaces.
From main distribution valves, a piping system is used to distribute the gas to the discharge nozzles which are places uniformly throughout the protected spaces.

Activation of the system

When releasing the system, the main distribution valve opens. The pilot gas to the pressure operated CO2 cylinder top valves is delayed for a specified time.
After the delay, the cylinder top valves open the gas are discharged through the piping and nozzles into the protected space.
There are several methods for system activation:
·        Quickly release the system by pressure operated cylinder top valves 
·        Manually release the CO2 cylinders individually one by one or by group in sequence depending upon the state of fires

CO2 is a colourless, non-corrosive gas that causes no chemical reaction to metals, electrical equipments, oil and has no mechanical damage to applied surfaces. It is commonly compressed to the liquid state in high pressure cylinders for storage and it can be stored for an indefinite time.
After the Unitor CO2 System is released, CO2 concentration quickly increases in the space and it suppresses the oxygen content to successfully extinguish the fire. It is proven to be a fast acting fire extinguishing agent and is effective on deep seated fires in cargo holds. In addition, it leaves no residue to clean up so your vessel can be back in operation almost straightaway.
At the same time, CO2 is also highly suffocative. It must be avoided by personnel when released. The Unitor CO2 system is designed with a pre-alarm system and a time delay function to allow the evacuation of the hazard area and avoid danger to the crew.
Thats All Folks :)

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1 comment:

  1. nowadays co2 bottles in a systems are not dedicated to engine room. same set of bottles can be used for cargo hold as well.Therefore, drawings done for the examination purposes may indicate the facility for using the bottles for the cargo holds or pumprooms as required.

    ReplyDelete

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