Foam and CO2 Systems

How CO2 and foam put out fires

A CO2 total flooding system fills a closed space with carbon dioxide until the oxygen level is too low for combustion. The concentration that does this is lethal to people. The space must be evacuated before release, so the system has two separate release controls, a time delay and a pre-discharge alarm. Under the FSS Code the alarm sounds for at least 20 seconds before the gas is released.

A foam system mixes concentrate with firewater through a proportioner and expands it with air. The foam blankets a burning liquid, cuts off oxygen and stops vapour release. Low-expansion foam suits helidecks and fuel areas. High-expansion foam fills an enclosed machinery space.

Configurations

Key specifications

Standards and service intervals

Chapter 5 of the FSS Code covers CO2. For machinery spaces, 85 percent of the gas must discharge within 2 minutes. IMO MSC.1/Circ.1318/Rev.1 sets CO2 maintenance:

• Contents of each cylinder checked every two years by weight or level gauge
• At ten years, at least 10 percent of cylinders internally inspected and hydrostatically tested, rising to 50 percent and then all if any fail
• Every cylinder hydrostatically tested before its 20th anniversary and every ten years after
• Flexible hoses replaced at the maker's interval and at least every ten years

Foam systems fall under FSS Code chapter 6 for machinery spaces, chapter 14 for deck foam and chapter 17 for helicopter facilities. MSC.1/Circ.1312 requires the first lab test of concentrate no more than three years after supply, then every year. On UK helidecks, CAP 437 applies and the 2009 MODU Code has its own helicopter facilities chapter.

PFOS and PFAS rules for foam

From 1 January 2026, SOLAS chapter II-2 as amended by MSC.532(107) bans using or storing extinguishing media containing PFOS above 10 mg/kg. Removed media goes to a shore reception facility. The EU Regulation (EU) 2025/1988 restricts all PFAS in firefighting foams, with transition periods by use. Older AFFF and film-forming fluoroprotein concentrates are now a disposal liability. A fluorine-free replacement may need a different induction rate, nozzles or approval, so confirm the system is approved with it.

Failure modes and inspection

• Cylinder corrosion at the base and under the brackets
• Leaking cylinder valves, found by weight loss
• Release cabinet switches, pull cables, pilot cylinders and time delay
• Manifold check valves and directional valves
• Foam concentrate out of specification on lab test
• Proportioners and monitors seized from seawater and salt
• Foam tank internal coating and bladder condition

Documentation

• Cylinder test certificates with serial numbers and stamped dates
• Last contents check and service report
• System approval, calculation and drawings
• Foam concentrate type, batch, supply date and last lab report
• PFOS-free certificate for any foam concentrate

Integration and compatibility

A replacement cylinder must match the valve type, pilot actuation and manifold of the installed bank. Check CO2 room space, ventilation and floor loading. Foam skids need a firewater supply that covers the foam demand plus other systems running at the same time. Monitors and nozzles must match the helideck size and the concentrate approval.

Recertification and buying used

Used CO2 cylinders with recent test stamps are worth buying as like-for-like replacements. Older banks will need hydrostatic testing soon after purchase. Unused surplus foam skids and monitors from cancelled projects are good buys if they suit a fluorine-free concentrate. Old fluorinated concentrate is worth less than its disposal cost. Naventr can arrange an inspection of a cylinder bank or foam skid on request. Kidde and Minimax supply CO2 and foam systems. For gas and mist alternatives, see fixed fire suppression.