Ship Cargo Hold CO2 System: NFPA 12, SOLAS II-2 and Total Flooding

Cargo hold fires on container and general cargo ships are a serious risk — in the 2019 Maersk Honam incident the ship burned for a full month. NFPA 12 (Carbon Dioxide Extinguishing Systems) and SOLAS II-2 define fixed CO2 systems for cargo holds, engine rooms and pump rooms. The system discharges from a CO2 cylinder battery bank as total flooding. This article covers the backbone of shipboard CO2 design, concentration selection and the problems that arise by cargo type.

Total Flooding Concentrations

• General cargo hold: 30 percent
• Container hold: 30 percent
• Ro-Ro deck: 40 percent (gasoline vehicles)
• Engine room (diesel): 40 percent
• Engine room (gas turbine): 50 percent

CO2 Quantity Calculation

Typical calculation for a 5,000 m³ hold at 30 percent concentration:

• Gross volume x factor (NFPA 12 Table 5.3.3)
• 5,000 m³ × 0.56 kg/m³ = 2,800 kg CO2
• With 45 kg cylinders: 2,800 / 45 = 62.2, i.e. 63 cylinders
• Discharge time 1 min — up to 2 min for a deep-seated fire
• Hold time: concentration maintained for at least 20 min

Battery Bank and Manifold

• CO2 cylinder room: outside the protected space, in a fire-separated compartment
• Manifold: cylinders connected in parallel through check valves
• Pilot cylinder: for manual release and as backup
• Alarm: 20-second delay for personnel evacuation
• Pilot line: two release stations

Cargo-Type Challenges

• Container: CO2 cannot penetrate the container; it only inerts the hold void space
• Lithium battery container: CO2 does not stop thermal runaway — it only cuts oxygen while the reaction continues inside the battery
• Dangerous goods (IMDG): Class 3 and 4.1 cargo must be stowed on a separate deck or in a separate hold
• Hot hold: holds next to the engine room stay warmer, lowering the ignition threshold

2019 Maersk Honam Case

• Indian Ocean, 7,700 TEU container ship
• Calcium hypochlorite container — incorrect stowage
• CO2 flooding was ineffective because the fire was inside the containers
• 5 crew members died
• Stowage rules were subsequently revised at IMO MSC 101

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