Fixed fire systemsLesson 1 of 8
Fixed fire systems on board: what is required where
A map of which fixed fire system each space on a ship needs, how much extinguishing medium is enough, and where to find the rule.
15 minutes · Open to everyone · Rules checked 20 October 2026
Start here
Every ship carries fire systems that nobody on board chose. The shipyard fitted them because SOLAS chapter II-2 said so, and the Fire Safety Systems (FSS) Code said how they must perform. When you join as chief engineer, superintendent or surveyor, the first question is: what should be here, and is it all here? Port State control (PSC) inspectors start with the same question.
The answer depends on the space. An engine room, a container hold, a car deck, a cargo pump-room, a cabin corridor and a galley each carry a different fire risk, so the rules give each a different system. This lesson is the map. The rest of the course goes into each system in detail.
Try it
How much CO2 does the largest protected space need?
In plain words
Fire needs three things: fuel, heat and oxygen. A fixed system takes one or more of them away, automatically or at the push of a lever, without the crew having to walk into the fire.
- Gas systems (mostly carbon dioxide, CO2) fill a closed space with gas until there is too little oxygen for the fire. They work only if the space is sealed, and they are deadly to anyone inside.
- Foam systems cover burning oil with a blanket, or fill a whole space with light foam.
- Water systems (sprinklers, water spray, water mist) cool the fire and the air. Water mist uses tiny droplets that turn to steam and also push oxygen away.
- Detection systems do not put the fire out. They find it early and raise the alarm, which matters just as much.
- Passive protection (steel bulkheads, fire doors, fire dampers in ducts) keeps a fire inside the space where it started.
The rule book links each space to the systems it may use: an engine room may have CO2, high-expansion foam or water spray; cargo holds normally have CO2; a passenger ship’s cabins have sprinklers; a deep-fat fryer has its own small system. The calculator above shows how the amount of CO2 is worked out: a fixed percentage of the volume of the largest protected space.
In detail
The main rule: SOLAS II-2/10 and the FSS Code
SOLAS regulation II-2/10 says which spaces need fixed fire-extinguishing systems. The FSS Code, made mandatory by SOLAS, says how each type of system must be built and how much medium it needs. The FSS Code chapters you will use most are:
| FSS Code chapter | System |
|---|---|
| 5 | Fixed gas systems (CO2, and equivalents such as inert gas or clean agents) |
| 6 | Fixed foam systems (high-expansion and low-expansion) |
| 7 | Fixed pressure water-spraying and water-mist systems |
| 8 | Automatic sprinkler, fire detection and fire alarm systems |
| 9 | Fixed fire detection and fire alarm systems |
| 10 | Sample extraction smoke detection systems |
| 14 | Fixed deck foam systems (tankers) |
Machinery spaces of category A
Machinery spaces of category A (spaces with internal combustion machinery used for main propulsion, or for other purposes above a power threshold, or with oil-fired boilers or oil fuel units) must have one of three fixed systems: a fixed gas system (FSS Code chapter 5), a fixed high-expansion foam system (chapter 6) or a fixed pressure water-spraying system (chapter 7). Water mist is accepted as an equivalent water-based system when it is approved under MSC/Circ.1165, as amended.
On top of that, machinery spaces of category A above 500 m³ on passenger ships of 500 GT and over and cargo ships of 2,000 GT and over need a fixed local application system: a water-based system aimed at the hot spots (the fire-hazard parts of internal combustion machinery, boiler fronts, incinerators and purifiers for heated fuel oil). It must work without stopping the engines, evacuating the space or sealing it. For ships built on or after 1 July 2014 it covers the fire-hazard parts of all internal combustion machinery, not only main propulsion and power generation.
Portable foam is also required: at least one portable foam applicator unit and enough 45-litre foam extinguishers to reach any part of the fuel and lube oil pressure systems.
Cargo spaces
| Ship and space | Fixed system |
|---|---|
| Cargo ships of 2,000 GT and over, cargo spaces other than ro-ro and vehicle spaces | Fixed CO2 or inert gas system, or a system giving equivalent protection |
| Passenger ships of 1,000 GT and over, cargo spaces | Fixed CO2 or inert gas system, or high-expansion foam giving equivalent protection |
| Ships carrying dangerous goods | Fixed CO2 or inert gas system, or equivalent for the cargoes carried |
| Ro-ro and vehicle spaces that can be sealed (not special category) | Fixed gas, high-expansion foam or fixed water-based system |
| Ro-ro and vehicle spaces that cannot be sealed, and special category spaces | Fixed water-based system (MSC.1/Circ.1430/Rev.3 for new approvals) |
The Administration may exempt cargo spaces of a ship built and used only for ore, coal, grain, unseasoned timber, non-combustible or low fire-risk cargoes, provided it has steel hatch covers and can close all ventilators. The exemption must be recorded on an Exemption Certificate with the list of permitted cargoes. MSC.1/Circ.1395/Rev.7 lists the solid bulk cargoes for which a fixed gas system may be exempted, or is ineffective.
Tankers
Tankers carry a fixed deck foam system (FSS Code chapter 14) for the cargo deck. Cargo pump-rooms need CO2, high-expansion foam or pressure water spray, operated from outside the pump-room. Where CO2 is used, a notice at the controls must say it is for fire extinguishing only and not for inerting, because of the electrostatic ignition hazard, and its alarms must be safe in a flammable atmosphere.
Accommodation, service spaces and galleys
- Passenger ships carrying more than 36 passengers: an automatic sprinkler, fire detection and fire alarm system in control stations, accommodation and service spaces, including corridors and stairways.
- Cargo ships: an automatic sprinkler system only where protection method IIC is chosen; methods IC and IIIC rely on detection.
- Paint lockers: CO2 for 40% of the gross volume, dry powder at 0.5 kg/m³, water at 5 l/m²/min, or an equivalent, all operable from outside.
- Deep-fat cooking equipment and galley exhaust ducts: their own fixed systems (lesson 5).
How much CO2: the formula behind the calculator
The FSS Code, chapter 5, paragraph 2.2.1, sets the free-gas volume as a percentage of the gross volume of the largest space the system protects:
| Space | Free CO2 volume |
|---|---|
| Cargo spaces | 30% of the gross volume of the largest cargo space |
| Machinery spaces | The larger of 40% of the gross volume excluding the casing above the level where its horizontal area is 40% or less of the space, or 35% of the gross volume including the casing |
| Vehicle and ro-ro spaces (not special category) that can be sealed | 45% of the gross volume of the largest such space |
Free gas is converted to mass at 0.56 m³/kg:
CO2 mass (kg) = percentage × gross volume (m³) ÷ 0.56
Worked example. An engine room is 5,000 m³ including the casing and 4,000 m³ without the upper casing. 40% of 4,000 = 1,600 m³; 35% of 5,000 = 1,750 m³. The larger figure governs: 1,750 ÷ 0.56 = 3,125 kg. With cylinders of 45 kg each (a common size, used here only as a rule of thumb), that is 70 cylinders. The volume of the starting air receivers, as free air, must be added to the machinery space volume unless their safety valves discharge to open air.
The system must also be able to deliver the gas fast enough: 85% into a machinery space within 2 minutes, and at least two thirds into a container or general cargo space within 10 minutes (20 minutes for a solid bulk cargo space). Cargo hold controls must allow one third, two thirds or the whole quantity to be released, depending on how full the hold is.
What has changed and what is coming
- Halon (1211, 1301, 2402) and perfluorocarbon systems are prohibited for new installations. A few old ships still have halon; some flags, such as the Bahamas, allow refilling a discharged existing system while strongly advising replacement.
- PFOS foam: since 1 January 2026, SOLAS II-2/10.11 bans the use or storage of fire-extinguishing media containing perfluorooctane sulfonic acid (PFOS) on new ships. Ships built before then must comply by the first survey on or after 1 January 2026 (lesson 3).
- Ro-ro passenger ships built on or after 1 January 2026 need a fixed water-based system with monitors for weather decks used for vehicles (FSS Code chapter 7, section 2.5), and new alarm presentation rules for detection (FSS Code chapter 9).
- IMO is working on better fire detection and fire-fighting for containers on and under deck. No amendment had been adopted by 20 October 2026; watch the reports of the Sub-Committee on Ship Systems and Equipment (SSE).
What the rules say
- SOLAS regulations II-2/10.4.1.1, 10.5.1.1 and 10.5.2.1 require category A machinery spaces with oil-fired boilers, oil fuel units or internal combustion machinery to have a fixed gas, high-expansion foam or fixed pressure water-spraying system complying with the FSS Code.1
- SOLAS regulation II-2/10.5.6 requires a fixed water-based local application system in category A machinery spaces above 500 m³ on passenger ships of 500 GT and over and cargo ships of 2,000 GT and over, with automatic and manual release in periodically unattended spaces.12
- SOLAS regulation II-2/10.4.1.3 states that systems using “Halon 1211, 1301, and 2402 and perfluorocarbons shall be prohibited”.1
- SOLAS regulation II-2/10.4.3 requires CO2 stored outside the protected space to be kept in a room used for no other purpose, with outward-opening doors and, if below deck or without access from open deck, mechanical exhaust ventilation of at least 6 air changes per hour from the bottom of the space.1
- SOLAS regulation II-2/10.7.1.3 requires cargo spaces of cargo ships of 2,000 GT and over, other than ro-ro and vehicle spaces, to be protected by a fixed CO2 or inert gas system or an equivalent system.1
- SOLAS regulation II-2/10.7.1.4 allows the Administration to exempt cargo spaces of ships solely intended for low fire-risk cargoes, provided the ship has steel hatch covers and an Exemption Certificate lists the permitted cargoes.16
- SOLAS regulation II-2/20.6.1, for ships built on or after 1 July 2014, requires a fixed gas, high-expansion foam or water-based system in ro-ro and vehicle spaces that can be sealed, and a fixed water-based system in spaces that cannot be sealed and in special category spaces.27
- FSS Code chapter 5, paragraphs 2.2.1.1 to 2.2.1.5, sets CO2 at 30% of the largest cargo space, 45% of the largest sealable ro-ro or vehicle space, and the larger of 40% (without casing) or 35% (with casing) of the largest machinery space, calculated at 0.56 m³/kg.3
- FSS Code chapter 5, paragraph 2.2.1.6, requires that 85% of the gas can be discharged into a machinery space within 2 minutes; paragraph 2.2.1.7 requires two thirds within 10 minutes for container and general cargo spaces and within 20 minutes for solid bulk cargo spaces.3
- SOLAS regulation II-2/10.11, added by resolution MSC.532(107), prohibits the use or storage of extinguishing media containing PFOS; ships built before 1 January 2026 must comply by the first survey on or after that date.4
Flag and class notes
- Bahamas (Marine Notice 79, version 2.2, November 2025) accepts non-asphyxiating clean agents such as “Novec 1230” and “FM 200” (HFC-227ea) in machinery spaces for which SOLAS prescribes no specific system, on conditions agreed case by case and only where the space is not connected to accommodation. It also accepts replenishment of a discharged existing halon system but strongly recommends a replacement plan, and warns that a ship may be detained where local law forbids halon refilling.5
- Marshall Islands (Marine Notice 2-011-14, August 2025) accepts water delivered by equivalent means under SOLAS II-2/19.3.1.2 where a fixed gas system has been found ineffective for the cargoes listed in MSC.1/Circ.1395, subject to verification by the recognised organisation (RO).8
- Class (IACS): Unified Interpretation SC132 says “conventional cargo spaces” (cargo spaces other than ro-ro spaces or container holds with integral reefer containers) need not have the automatic release alarm, and SC252 requires the sequence of the two CO2 release controls to be enforced by a mechanical or electrical interlock, not by procedure.3
Key numbers
| What | Value |
|---|---|
| CO2 for cargo spaces | 30% of gross volume of largest cargo space3 |
| CO2 for machinery spaces | Larger of 40% (excl. upper casing) or 35% (incl. casing)3 |
| CO2 for sealable ro-ro and vehicle spaces | 45% of gross volume of largest such space3 |
| Free-gas conversion | 0.56 m³ per kg of CO23 |
| Machinery space discharge | 85% within 2 min3 |
| Container and general cargo hold discharge | Two thirds within 10 min3 |
| Solid bulk cargo hold discharge | Two thirds within 20 min3 |
| Pre-discharge alarm before release | At least 20 s3 |
| CO2 room exhaust ventilation (below deck) | At least 6 air changes per hour1 |
| Local application required in category A machinery spaces | Above 500 m³; passenger ships 500 GT+, cargo ships 2,000 GT+1 |
| PFOS foam ban, existing ships | By first survey on or after 1 January 20264 |
What inspectors find
- In the 2012 joint Paris and Tokyo MOU campaign on fire safety systems, the question “Are the fire protection systems, fire-fighting systems and appliances maintained ready for use?” was answered “no” in 11% of 6,606 Tokyo MOU inspections, the worst result in the campaign.9
- In the same campaign, the fire main isolating valves were not marked, maintained or easily operable in 5.9% of inspections, and the fixed gas pre-discharge alarm failed its test in 1.4%.9
- In the 2023 joint campaign on fire safety, Tokyo MOU inspectors found 2,860 deficiencies on 1,287 ships in 7,190 campaign inspections and detained 88 ships for campaign items. Of the fire drills witnessed during the campaign, 8.44% were unsatisfactory.10
- Items the annual inspection and PSC checks are meant to catch: openings left in the boundaries of CO2-protected spaces, CO2 rooms used as storerooms, and maintenance plans that miss systems in the SOLAS II-2/14 list.11
Questions people ask
Can a water mist system replace CO2 in an engine room?
Yes, if it is approved as equivalent to the fixed systems in SOLAS II-2/10 under the IMO guidelines (MSC/Circ.1165, as amended), and the approval covers your engine room’s volume and layout. Water mist is also the usual choice for the local application system.
Why is the CO2 quantity based on the largest space and not the total?
The system is designed to fight one fire at a time. One set of cylinders can serve several spaces through normally closed section valves, so it only needs enough gas for the space that demands the most (FSS Code chapter 5, paragraph 2.1.1.1).
Does a bulk carrier need CO2 in its holds?
Not always. SOLAS II-2/10.7.1.4 lets the Administration exempt holds of a ship built and used only for low fire-risk cargoes such as ore, coal or grain. The exemption must be on an Exemption Certificate with the list of permitted cargoes, and the ship must have steel hatch covers and closable ventilators.
Check yourself
5 questions. Pass with 60% to mark the lesson as done.
Sources
- 1 IMO Resolution MSC.99(73), Adoption of amendments to SOLAS 1974 (revised chapter II-2, adopted 5 December 2000, in force 1 July 2002), annex, chapter II-2, regulation 10 (paragraphs 4, 5, 6 and 7), as later amended. Consolidated text: IMO SOLAS publication. https://wwwcdn.imo.org/localresources/en/KnowledgeCentre/IndexofIMOResolutions/MSCResolutions/MSC.99(73).pdf
- 2 IMO Resolution MSC.338(91), Amendments to SOLAS 1974 (adopted 30 November 2012, in force 1 July 2014), annex, amendments to regulations II-2/10.5.6.3 and II-2/20.6.1. https://wwwcdn.imo.org/localresources/en/KnowledgeCentre/IndexofIMOResolutions/MSCResolutions/MSC.338(91).pdf
- 3 International Code for Fire Safety Systems (FSS Code), resolution MSC.98(73), chapter 5 as replaced by resolution MSC.206(81) and amended by resolution MSC.339(91) (in force 1 July 2014), paragraphs 2.1.1, 2.1.3, 2.2.1, 2.2.2 and 2.4; with IACS Unified Interpretations SC132 (Rev.4) and SC252. https://wwwcdn.imo.org/localresources/en/KnowledgeCentre/IndexofIMOResolutions/MSCResolutions/MSC.339(91).pdf
- 4 IMO Resolution MSC.532(107), Amendments to SOLAS 1974 (adopted 8 June 2023, in force 1 January 2026), annex, new regulations II-2/1.2.10 and II-2/10.11. https://wwwcdn.imo.org/localresources/en/KnowledgeCentre/IndexofIMOResolutions/MSCResolutions/MSC.532(107).pdf
- 5 Bahamas Maritime Authority, Marine Notice 79, Firefighting Equipment, version 2.2 (20 November 2025), sections 7, 8 and 12. https://www.classnk.or.jp/hp/pdf/activities/statutory/solas/solas_treaty/fire_protection/circular/ci_fi_bahama.pdf
- 6 Liberian Registry, IMO MSC 110 meeting summary (2025), listing MSC.1/Circ.1395/Rev.7, Lists of solid bulk cargoes for which a fixed gas fire-extinguishing system may be exempted or for which a fixed gas fire-extinguishing system is ineffective. https://www.liscr.com/marketing/liscr/media/liscr/online%20library/maritime/msc-110-meeting-summary.pdf
- 7 Hong Kong Marine Department, Merchant Shipping Information Note 55/2023 (4 September 2023), on MSC.1/Circ.1430/Rev.3, Revised guidelines for the design and approval of fixed water-based fire-fighting systems for ro-ro spaces and special category spaces (applies to systems installed on or after 1 January 2024). https://www.mardep.gov.hk/en/msnote/pdf/msin2355.pdf
- 8 Republic of the Marshall Islands Maritime Administrator, Marine Notice 2-011-14, Maintenance, testing and inspection of fire protection systems and appliances (Rev. Aug/2025), section 5.5. https://www.register-iri.com/wp-content/uploads/MN-2-011-14.pdf
- 9 Tokyo MOU, Report of the 2012 Concentrated Inspection Campaign (CIC) on Fire Safety Systems (November 2013), section 3, questionnaire results. https://www.tokyo-mou.org/wp/wp-content/uploads/Final-Tokyo-MOU-Report-FSS-CIC-public-web-site.pdf
- 10 Tokyo MOU, Annual Report on Port State Control in the Asia-Pacific Region 2023, results of the 2023 CIC on Fire Safety, as summarised by SAFETY4SEA. https://safety4sea.com/tokyo-mou-psc-annual-report-2023
- 11 IMO MSC.1/Circ.1318/Rev.1, Revised guidelines for the maintenance and inspections of fixed carbon dioxide fire-extinguishing systems (25 May 2021), annex, section 5.1; and MSC.99(73), regulation II-2/14.2.2.3. https://www.mardep.gov.hk/en/msnote/pdf/msin2136anx1.pdf
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