CO2 fire extinguishing installations for cargo ship machinery spaces

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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.

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

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.

Figure :CO2 cutter type quick 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 63°C. 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:

Fire main system & related mechanism

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CO2 fire extinguishing installation

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Fire fighting equipments

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Details of fire detectors

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Machinery space fire & use of Walter Kidde CO2 system

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Fire protection system for cargo holds

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Low pressure CO2 storage

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Halon system

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Multi-spray system for the machinery spaces

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Automatic sprinkler system

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Details various portable extinguishers & how to use ?

.....more

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