14.2 Fixed Fire-Extinguishing Systems: CO2, Water Mist & Hi-Expansion Foam

14.2 Fixed Fire-Extinguishing Systems: CO2, Water Mist & Hi-Expansion Foam

When a major fire erupts in a ship's machinery space—fueled by ruptured fuel oil pipes, boiler blowbacks, or scavenge conflagrations—portable and mobile fire extinguishers are rapidly overwhelmed. In such catastrophic scenarios, ship survival depends upon fixed fire-extinguishing systems. Trainee General Purpose (GP) Ratings must thoroughly understand the engineering architecture, smothering mechanisms, operating sequences, and critical life-safety interlocks of the three primary fixed systems: High-Pressure Carbon Dioxide ($\text{CO}_2$) Total Flooding, Local Application Water Mist (Hyper-Mist), and High-Expansion Foam.

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1. Fixed High-Pressure Carbon Dioxide ($\text{CO}_2$) Total Flooding System

High-pressure $\text{CO}_2$ remains the most widely installed total flooding medium for engine rooms, pump rooms, and cargo holds on merchant ships. Because carbon dioxide is an inert, non-conductive gas that leaves no chemical residue, it extinguishes three-dimensional liquid spray fires without damaging electrical switchboards or delicate turbo-machinery.

                 FIXED HIGH-PRESSURE CO2 TOTAL FLOODING SYSTEM

      +-------------------------------------------------------------+
      | CO2 BATTERY ROOM (Dedicated deckhouse outside engine room)   |
      |                                                             |
      |   [Cyl] [Cyl] [Cyl] [Cyl] [Cyl] [Cyl] [Cyl] [Cyl] [Cyl]     |
      |     |     |     |     |     |     |     |     |     |       |
      |   +-----------------------------------------------------+   |
      |   | High-Pressure Distribution Manifold                 |   |
      |   +--------------------------+--------------------------+   |
      |                              |                              |
      |                     +--------v--------+                     |
      |                     | Main Stop Valve |                     |
      |                     +--------+--------+                     |
      |                              |                              |
      |   PILOT RELEASE CABINET      |                              |
      |   +---------------------+    |                              |
      |   | [Door Microswitch]  |    |                              |
      |   | (Alarm Initiation)  |    |                              |
      |   | [Pilot Gas Bottle]  |----+                              |
      |   | [Release Levers]    |    |                              |
      |   +---------------------+    |                              |
      +------------------------------|------------------------------+
                                     |
                                     | Distribution Pipe to Engine Room
                                     v
      +-------------------------------------------------------------+
      | MACHINERY SPACE (ENGINE ROOM)                               |
      |                                                             |
      |    (Nozzle)                  (Nozzle)             (Nozzle)  |
      |       v                         v                    v      |
      |    * * * *                   * * * *              * * * *   |
      |   * * * * *                 * * * * *            * * * * *  |
      |  * * * * * *               * * * * * *          * * * * * * |
      |  Tank Top Bilges         Cylinder Tops        Purifier Room |
      +-------------------------------------------------------------+

System Layout and Storage Architecture

1. $\text{CO}_2$ Battery Room:
   • Located outside the engine room boundaries, typically on the open boat deck or upper superstructure deck, with direct access from the open weather deck.
   • Keep the room within the system’s approved ambient-temperature limits. SOLAS requires bottom-extract mechanical ventilation of at least six air changes per hour for storage spaces below deck or without access from the open deck. High-pressure storage is distinct from refrigerated low-pressure CO2 storage.
   • Housed with dozens or hundreds of high-tensile seamless steel cylinders (each typically $45\text{ kg}$ or $67.5\text{ liter}$ capacity) pressurized with liquid $\text{CO}_2$ at approximately $57\text{ bar}$ at $20^\circ\text{C}$.
   • Cylinders are fitted with siphon dip-tubes extending to the cylinder bottom, ensuring liquid $\text{CO}_2$ is forced out under its own vapor pressure when released.
2. Distribution Manifold & Directional Valves:
   • Each cylinder is connected to a common high-pressure manifold via high-pressure flexible loops and non-return check valves.
   • Directional distribution section valves direct the gas charge to specific compartments: Engine Room, Auxiliary Boiler Space, Purifier Room, or Cargo Holds.
3. Discharge Nozzles:
   • Orifice and horn-type nozzles strategically distributed across three elevations: (1) beneath floor plates over bilge wells and pipe trenches, (2) over middle platform auxiliary machinery, and (3) around the upper deckhead casing.

Extinguishing Mechanism & SOLAS Performance Criteria

• Oxygen Displacement (Smothering): Atmospheric air contains approximately $20.95\%\text{ O}_2$. Hydrocarbon liquid fires require at least $15\%\text{--}16\%\text{ O}_2$ to sustain open combustion. When discharged, high-pressure $\text{CO}_2$ gas—which is $1.5\text{ times heavier than air}$—expands rapidly across the space, diluting the oxygen available for combustion to suppress the fire. Retain the extinguishing concentration and keep the space closed while hot machinery cools; premature ventilation can cause re-ignition.
• FSS Code Chapter 5 Performance Requirement:

Release Preparations, Controls & Safety Interlocks

CO2 flooding creates a life-threatening atmosphere. Follow the ship’s emergency plan and the operating instructions posted at the release station. The Master, or the responsible officer authorized by the ship’s procedures, directs release after the safety preparations have been verified.

                    CO2 RELEASE — CHECK THE SHIP’S INSTRUCTIONS
  Evacuate protected space -> Account for everyone / verify headcount
                              |
                              v
  Stop ventilation -> Close dampers, skylights and other gas/air openings
                              |
                              v
  Stop affected machinery/pumps -> Isolate fuel/oil feeds as directed
                              |
                              v
  Authorized release -> Confirm correct space and pre-discharge warning
                              |
                              v
  Open distribution valve -> Release CO2 from the storage cylinders

1. Evacuate and Account for Personnel: Leave by safe escape routes and muster as directed. Confirm that everyone has left the protected space and complete the headcount before discharge. Report anyone missing immediately.
2. Isolate Ventilation and Close the Space: Operate the remote fan stops and close the relevant dampers, skylights and other openings that admit air or allow gas to escape. Verify closure; do not assume a release-cabinet switch has stopped every fan.
3. Stop Machinery and Fuel Feed: Stop the machinery and oil pumps in the affected space and operate the designated quick-closing valves under the emergency plan. Prevent continued fuel or oil supply to the fire.
4. Select and Check the Release Station: Confirm that the controls serve the correct space. If the release box is locked, the FSS Code requires its key in a conspicuous adjacent break-glass enclosure. Follow the installed controls and instructions.
5. Pre-Discharge Warning: The audible and visual alarm starts automatically, for example when the cabinet door opens. It must sound for the time needed to evacuate, never less than 20 seconds before discharge. The alarm is an immediate escape signal; it does not replace the evacuation and headcount check.
6. Operate the Two Release Controls: First open the distribution valve to the selected protected space, then discharge the storage cylinders. Approved interlocks ensure the correct sequence. Pilot-gas actuation is a common arrangement, but the exact levers and controls are those shown in the ship’s instructions.

Asphyxiation, Cryogenic & Post-Discharge Hazards

• Lethal Exposure Hazard: Carbon dioxide is colourless and odourless. High concentrations have direct toxic effects as well as reducing available oxygen, and can rapidly cause unconsciousness and death. Never rely on symptoms or a supposedly safe delay: evacuate before release, account for personnel, and prevent unauthorized re-entry.
• Cryogenic Temperatures & Static Electricity: Discharge can produce very cold gas and dry-ice particles. At atmospheric pressure, dry ice sublimes at $-78.5^\circ\text{C}$. Avoid skin contact with cold discharge equipment and liquid or solid CO2 because of frostbite risk. Maintain the system’s bonding and earthing arrangements.
• Post-Discharge Waiting Period & Re-Entry Protocol:

2. Local Application Water Mist Systems (Hyper-Mist)

Local application water-based systems can suppress a fire at its source promptly, while preparations for any necessary total flooding continue. Unlike CO2 flooding, activation does not require prior shutdown, sealing or evacuation of the whole space.

SOLAS II-2/10.5.6 applies to passenger ships of 500 GT and above and cargo ships of 2,000 GT and above. Machinery spaces of category A above 500 m³ require an approved fixed water-based or equivalent local application system, in addition to the main fixed system. Water mist is a common solution; high-pressure equipment is one example.

                 LOCAL APPLICATION WATER MIST — EXAMPLE  

     +--------------------+   +-----------------------+
     | Fresh Water Supply |---> High-Pressure Plunger |
     | Storage Tank       |   | Pump (100 to 140 bar)  |
     +--------------------+   +-----------+-----------+
                                          |
                                          v High-Pressure Stainless Main
   +--------------------------------------+-----------------------------------+
   |                          |                           |                   |
   v Section Valve A          v Section Valve B           v Section Valve C   v
+--------------------+   +--------------------+   +--------------------+  +---+
| MAIN ENGINE TOPS   |   | DIESEL GENERATORS  |   | PURIFIER ROOM      |  |BOI|
| Micro-Nozzles      |   | Micro-Nozzles      |   | Micro-Nozzles      |  |LER|
| [Atomized Droplets]|   | [Atomized Droplets]|   | [Atomized Droplets]|  |   |
| (50-100 microns)   |   | (50-100 microns)   |   | (50-100 microns)   |  |   |
+--------------------+   +--------------------+   +--------------------+  +---+

Local Protection Areas

Local application systems protect selected hazards rather than flooding the entire engine room. Instead, specialized micro-nozzles are positioned directly above specific high-risk fire zones:

1. Main engine cylinder heads, fuel injection pumps, and high-pressure fuel rails.
2. Auxiliary diesel generator cylinder tops, exhaust lines, and turbochargers.
3. Marine auxiliary boiler burner fronts, fuel valve manifolds, and furnace doors.
4. Purifiers for heated fuel oil; other oil-treatment hazards may also be covered by the approved design.
5. Waste incinerator burner fronts and fuel pumps.

Operating Principles & Dual Extinguishing Kinetics

• High-Pressure Example: A plunger pump can deliver water through stainless steel piping at $100\text{--}140\text{ bar}$. Actual pressure, supply and nozzle arrangement are those of the approved system; a local section may share a suitably designed water-based main system.
• Micro-Droplet Atomization: Specialized micro-orifice spray nozzles shatter the high-pressure water stream into a dense, fog-like mist with droplet diameters of $50\text{--}100\text{ microns}$ ($0.05\text{--}0.1\text{ mm}$).
• Extinguishing Action 1: Enormous Surface Cooling:
  • By atomizing $1\text{ liter}$ of water into 50-micron droplets, the total water surface area is approximately $120\text{ square meters}$.
  • These micro-droplets absorb the high latent heat of vaporization of water ($2,260\text{ kJ/kg}$) instantly, cooling the flame zone and adjacent fuel surfaces below ignition temperatures.
• Extinguishing Action 2: Localized Oxygen Starvation (Steam Expansion):
  • As the micro-droplets vaporize, they expand $1,700\text{ times}$ in volume into water steam.
  • This sudden steam expansion displaces oxygen in the immediate vicinity of the hotspot, helping suppress the fire locally. This does not make the surrounding fire atmosphere safe to breathe.

Activation and Watchkeeper Safety

• Immediate Local Suppression: Activation does not require prior engine shutdown, personnel evacuation, ventilation shutdown or sealing of the space. This allows prompt attack on a developing fire.
• Fire Hazards Remain: Smoke, heat, steam and oxygen depletion can still endanger personnel. Follow the alarm and emergency plan, escape when required, and use suitable breathing apparatus for firefighting. Do not interpret water discharge as an all-clear.
• Release Modes: Periodically unattended machinery spaces require both automatic and manual release; continuously manned spaces require manual release. Automatic systems use approved detection arrangements, such as two flame detectors or a flame-and-smoke combination. Know the installed controls and section indications.

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3. High-Expansion Foam Systems

High-expansion foam systems represent another powerful total-flooding alternative, particularly on roll-on/roll-off (Ro-Ro) vessels, tanker pump rooms, and specialized container engine rooms.

                 OUTSIDE-AIR FOAM GENERATOR — EXAMPLE     

   Water Main (Fire Pump) + Foam Concentrate Tank
                |
                v Proportioner (Injects 2% to 3% Concentrate)
      +-------------------------------------------------------------+
      | Foam Solution Delivery Pipeline                             |
      +-----------------------------+-------------------------------+
                                    |
                                    v
                     +-----------------------------+
                     | HIGH-EXPANSION FOAM GEN     |
                     |                             |
     Fresh Air Duct  |   [ Spray Nozzles ]         |
     ==============> |          |  |               |
     (Air Fan Driven)|          v  v               |
                     |   [ Fine Wire Mesh Net ]    |
                     |      O O O O O O O O        |
                     |     O O O O O O O O O       |
                     +--------------+--------------+
                                    |
                                    v
           Continuous Blanket of Featherweight Bubbles (500:1 to 1000:1)
           Submerges Entire Machinery Space from Tank Top to Overhead!

Foam Expansion Ratios & Mechanics

• Expansion Ratio: Defines the volume of expanded foam generated from a given volume of liquid water-concentrate solution. Typical high-expansion systems may produce expansion ratios of $500:1\text{ to }1000:1$ (one cubic meter of liquid yields 500 to 1,000 cubic meters of foam).
• Foam Generation: The proportioner mixes water and the system’s approved concentrate at its specified concentration. In an outside-air system, a fan forces fresh air through a screen wetted by the foam solution. Inside-air systems instead generate foam using air from the protected space. Use the matched generator/concentrate arrangement and the ship’s operating instructions.

Fire Suppressing Mechanism

1. Smothering: The rapid buildup of foam completely blankets all bilge surfaces, pipes, and fuel tanks, sealing off liquid fuel surfaces from atmospheric oxygen.
2. Cooling: As the bubble lattice contacts hot metal, the thin water film vaporizes, cooling the steel and generating steam that further dilutes oxygen.
3. Thermal Insulation & Smoke Scrubbing: The foam blanket acts as a thermal barrier, blocking radiant heat transfer to unignited fuel tanks and trapping toxic soot and smoke particles within the bubble structure.

Escape and Post-Discharge Hazards

Evacuate on the pre-discharge warning; foam can obscure exits and impair hearing and orientation. If caught during discharge:

• Don an EEBD immediately if available and continue along the escape route.
• Keep contact with a handrail or bulkhead to maintain direction; clear foam from the face as needed to escape.
• Do not rely on air in foam bubbles for breathing: the blanket may contain oxygen-deficient air and toxic combustion products.
• Re-entry after discharge requires a controlled plan and suitable breathing apparatus. Do not enter to search for a casualty without the trained team and back-up arrangements.