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CO2 fire extinguishing installations for cargo ship machinery spaces

Fire extinguishing installations employing CO2 stored under pressure at ambient temperature are extensively used to protect ships' cargo compartments, boiler rooms and machinery spaces. When released the CO2 is distributed throughout the compartment, so diminishing the relative oxygen content and rendering the atmosphere inert.

The quantity of CO2 required is calculated from the gross volume of the largest cargo space or machinery compartment, whichever is the greater of the two. Additional CO2 may be required for machinery spaces containing large air receivers. This is because air released from the cylinders through fusible plugs or over pressure release, would increase oxygen content in the space.

The high pressure carbon dioxide (CO2) system shown (Figure 14.11) is supplied from storage bottles of CO2 which are opened by a servo-piston operated gang release. A safety feature to protect against accidental release is provided by the master valve on the pipe to the engine room distribution nozzles.

Carbon dioxide system
Figure : Carbon dioxide system

The CO2 system is used if a fire is severe enough to force evacuation of the engine room or to prevent entry. An alarm is sounded by an alarm button as the CO2 cabinet is opened and in some ships there is also a stop for the engine room fans incorporated (Figure 14.12). Before releasing the CO2, personnel must be accounted for and the engine room must be in a shut down condition with all openings and vent flaps closed. It is a requirement that 85% of the required quantity of gas is released into the space within two minutes of actuating the system release.

Figure 14.12

CO2 cabinet alarm
Figure : CO2 cabinet alarm

In the installation shown, the actuating handle opens pilot cylinders of CO2 and the gas from these pushes the piston in the servo-cylinder down, to operate the gang release for the other bottles. To avoid sticking, all the handles must be in good alignment. The bottle valves may be of the quick-release type (Figure 14.13) where the combined seal and bursting disc is pierced by a cutter. The latter is hollow for passage of liquid CO2 to the discharge pipe. An alternative type of quick release valve (Figure 14.14) is held in place by a hinged linkage arrangement until released.

CO2 cutter type quick release
Figure :CO2 cutter type quick release

Valve type release
Figure :Valve type release

Bottle pressure is normally about 5 2 bar (750lb/in2) but this varies with temperature. Bottles should not be stored where the temperature is likely to exceed 55 deg C. The seal/bursting discs are designed to rupture spontaneously at pressures of 177 bar produced by a temperature of about 63C. The master valve prevents CO2 released in this way from reaching the engine room. Gas is released by the relief arrangement on the manifold, into the CO2 space where, in the event that the release was caused by a fire in the compartment, the fire would be extinguished.



Rapid injection of CO2 is necessary to combat an engine room fire which has attained such magnitude that the space has to be evacuated. Hence the rule that 85% of the gas must be released within two minutes. The quantity of gas carried (a) must be sufficient to give a free gas volume equal to 40% of the volume of the space except where the horizontal casing area is less than 40% of the general area of the space, or (b) must give a free gas volume equal to 35% of the entire space, whichever is greater. The free air volume of air receivers may have to be taken into consideration.

The closing of all engine room openings and vent flaps will prevent entry of air to the space. All fans and pumps for fuel, can be shut down remotely as can valves on fuel pipes from fuel service and storage tanks.

CO2 bottles are of solid drawn steel, hydraulically tested to 22 8 bar. The contents are checked by weighing or by means of a radioactive level indicator. Recharging is necessary if there is a 10% weight loss.

Pipework is of solid drawn mild steel, galvanized for protection against corrosion. The syphon tube in the bottle ensures that liquid is discharged from the bottles. Without the syphon tube the CO2 would evaporate from the surface giving a very slow discharge rate and, taking latent heat, would probably cause the remaining CO2 in the bottle to freeze.



Summarized below general cargo ship fire protection equipments & guideline:
  1. Fire main system & related mechanism

  2. The fire main extends to the full length of the ship and from the machinery spaces to the highest levels. Hydrants served by the main, are situated so that with suitable hoses any area on the ship can be reached. .....more

  3. CO2 fire extinguishing installation

  4. Fire extinguishing installations employing CO2 stored under pressure at ambient temperature are extensively used to protect ships' cargo compartments, boiler rooms and machinery spaces. When released the CO2 is distributed throughout the compartment, so diminishing the relative oxygen content and rendering the atmosphere inert. ...... more

  5. Fire fighting equipments

  6. Two independently powered pumps must be provided in all cargo ships of 1000 tons gross and over and in passenger ships of less than 4000 tons gross. Larger passenger vessels and passenger ferries must have three such pumps. The pumps are fitted with non-return valves if they are of the centrifugal type, to prevent loss of water back through open valves when not running. ..... more

  7. Details of fire detectors

  8. A variety of devices are available for detecting fire in unmanned machinery spaces but each has an ability to detect basically only one aspect. Thus, smoke detectors based on the ionization chamber are able to recognize combustion products but will not register radiation from a flame or heat. .....more

  9. Machinery space fire & use of Walter Kidde CO2 system

  10. Walter Kidde CO2 system employs pilot CO2 cylinders to open the distribution system main stop valve and subsequently the valves on the individual CO2 cylinders. .....more

  11. Fire protection system for cargo holds

  12. Holds for general cargo, have been protected against fire by fixed installations which deliver inert gas from an inert gas generator based on combustion of fuel (similar to the system available for inerting oil tankers) and halon systems. .....more

  13. Low pressure CO2 storage

  14. In some installations, the CO2 is stored in low pressure refrigerated tanks. The cylindrical storage vessels are fabricated to the pressure vessel requirements of the authorities. The tanks are of low temperature steel, fully tested and stress relieved. They are mounted on supports designed to withstand shock from collision. ..... more

  15. Halon system

  16. Halon 1301 has the chemical formula CF3 Br being known as bromo-trifluoromethane. It is a colourless, odourless gas with a density five times that of air and extinguishes fire by breaking the combustion chain reaction. .....more

  17. Multi-spray system for the machinery spaces

  18. This system is similar to the sprinkler used in accommodation areas but the spray heads are not operated automatically. The section control valves (Figure 14.20) are opened by hand to supply water to the heads in one or more areas. Ready to use hoses can also be supplied. Fresh water is used for the initial charging and the system is brought to working pressure by means of the compressed air connection. .....more

  19. Automatic sprinkler system

  20. A network of sprinkler heads is arranged throughout the spaces to be protected. Each sprinkler head is normally kept closed by a quartzoid bulb which is almost filled with a liquid having a high expansion ratio. .....more

  21. Details various portable extinguishers & how to use ?

  22. The first line of defence against fire in any area of the ship, is the portable fire extinguisher. Some common portable extinguishers that have been used at sea are described. .....more



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