CO2 Fire Suppression in Engine Rooms: Precautions, Actions, and Quantity Determination

Releasing CO2 into a ship's engine room for fire suppression is a critical procedure that demands strict adherence to safety protocols due to the asphyxiating nature of CO2. This section outlines the necessary precautions before release, actions to take immediately after release, and the factors determining the required quantity of CO2.

Before activating the CO2 fire suppression system in an engine room, paramount importance is placed on the safety of personnel and the effectiveness of the system. The following precautions are essential:

1. Evacuate and Account for All Personnel: This is the most crucial step. Ensure everyone has evacuated the engine room and conduct a thorough headcount to confirm no one remains inside. CO2 at fire suppression concentrations is lethal due to oxygen displacement.
2. Seal the Engine Room: All openings, including doors, hatches, ventilation flaps, and skylights, must be tightly closed and sealed. This prevents CO2 leakage and helps maintain the necessary concentration to smother the fire effectively.
3. Shut Down Machinery and Isolate Fuel: Stop the main engine, generators, and boiler within the engine room. Crucially, operate the remote quick-closing valves for fuel oil, hydraulic oil, and lubricating oil tanks and transfer lines. This prevents these combustibles from continuously feeding the fire.
4. Stop Ventilation Fans: Ensure all ventilation fans and blowers are stopped. This prevents fresh air from entering the engine room, which would counteract the CO2's smothering effect by reintroducing oxygen.
5. Verify System Readiness: Confirm that the CO2 system is in good working order and ready for activation. This includes checking the discharge nozzles, detectors, and ensuring the correct CO2 battery (bank of cylinders) is selected.
6. Inform Relevant Authorities: The nearest Coastguard should be notified as soon as practically possible when a fire incident requires CO2 system activation.

Why These Precautions Are Critical:

• Crew Safety: The primary reason is to protect the crew from the lethal effects of CO2. Failure to evacuate and account for personnel could result in fatalities from oxygen deprivation.
• Effective Fire Suppression: Properly sealing the engine room and stopping ventilation ensures that the CO2 can achieve and maintain the necessary concentration to effectively smother the fire by reducing the oxygen level.
• Preventing Re-ignition: Isolating fuel and oil supplies prevents the fire from being sustained and significantly reduces the risk of re-ignition after CO2 discharge.
• System Effectiveness: A well-maintained and ready CO2 system, coupled with properly secured openings, maximizes the chances of successful fire extinction with a single discharge, preventing further damage and potential loss of the vessel.

Once CO2 has been released into the engine room, immediate actions are necessary to manage the situation effectively and prevent re-ignition:

1. Confirm Release: Verify that the CO2 has been discharged by listening for the distinctive discharge sound, checking the temperature of the cylinders (they will feel cold), and visually inspecting the cylinder valves for activation.
2. Continue Cooling: Keep cooling the boundaries of the engine room (e.g., bulkheads, deckheads) from outside the space. This prevents the fire from spreading to adjacent areas due to heat transfer.
3. Avoid Re-entry: Do not re-enter the engine room immediately after CO2 release. The atmosphere will be critically oxygen-deficient and hazardous to life.
4. Delay Ventilation: Wait several hours before attempting any ventilation of the engine room. This extended waiting period ensures the fire is completely extinguished and the space has cooled sufficiently, minimizing the risk of re-ignition.
5. Seek Expert Advice: It is highly recommended to consult shore-side experts (e.g., technical managers, fire specialists) before attempting ventilation or re-entry. Their guidance is crucial for a safe and controlled recovery.
6. Plan for Safe Re-entry: When re-entry is deemed safe, it must only be done by trained personnel equipped with Self-Contained Breathing Apparatus (SCBA), safety lines, and with backup personnel standing by outside the space.
7. Thorough Ventilation: Before allowing normal entry without SCBA, ensure the engine room is thoroughly ventilated and tested for safe oxygen levels (approximately 21%). This may involve using portable fans or activating the ship's ventilation system at a low setting initially.
8. Prevent Re-ignition: During re-entry, avoid introducing any potential ignition sources. Combustible gases or hot spots might still be present, and introducing a spark could lead to re-ignition.

The effectiveness of CO2 fire suppression depends on achieving a sufficient concentration to displace oxygen and smother the fire. The required quantity of CO2 is primarily determined by:

• Volume of the Space: The total enclosed volume of the engine room or the specific protected area is a key factor.
• Type of Fire: While CO2 is effective against most Class B (flammable liquids) and Class C (electrical) fires common in engine rooms, the specific type might theoretically influence concentration requirements.
• Engine Room Specifics: Features like engine casings and other fixed structures within the engine room can impact the effective free volume and thus the amount of CO2 needed to achieve the desired concentration.

According to IMO regulations (specifically the FSS Code), the CO2 system must provide a minimum free gas volume. This is typically calculated based on the following criteria, with the largest calculated volume dictating the system size:

• At least 40% of the gross volume of the machinery space, excluding engine casings.
• For vessels under 20,000 GT (Gross Tonnage), at least 35% of the gross volume of the machinery space, including casings.
• If applicable (for cargo spaces protected by the same system), at least 30% of the largest cargo space volume.

The number of CO2 bottles required is determined by this highest volume requirement. As a general rule of thumb, one kilogram of liquid CO2 yields approximately 0.56 cubic meters of gas. Standard CO2 bottles typically hold 45 kg of liquid CO2. Therefore, the total number of bottles can be calculated using a formula based on the required total gas volume and the capacity of each bottle.

Furthermore, regulations also mandate a rapid discharge of the CO2, ensuring that the critical concentration is reached quickly to suppress the fire before it can spread further.