Start hereRules checked 20 October 2026
A sprinkler head is a small valve held shut by a glass bulb. It may hang over a cabin bed for twenty years, wet on the inside with stagnant water and exposed on the outside to steam, paint and cleaning sprays. On the day of a fire it has to open at the right temperature and spray the right pattern. Sprinkler heads that are corroded or clogged from the inside do not, and on ships that problem became serious enough for IMO to write a special testing procedure.
Water mist systems are now common in engine rooms, both as the main fixed system and as the local application system that sprays the hot spots on diesel engines and purifiers without stopping them. Ro-ro and car decks rely on large water spray (drencher) systems. This lesson covers all three: how they are built, how they are approved, and how they are tested.
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In this lesson
- The annual sprinkler test on a seven-year-old cruise ferry
- In plain words
- In detail
- What the rules say
- Flag and class notes
- Key numbers
- What inspectors find
- Quiz: 6 questions
Try it
The annual sprinkler test on a seven-year-old cruise ferry
In plain words
All three systems use water, but in different ways.
- Sprinklers protect cabins, corridors and public spaces. The pipes are always full of water under pressure. Each head opens on its own when its glass bulb bursts in the heat, so only the heads over the fire spray. An alarm tells the bridge which section is spraying, and a pump starts automatically to keep the water coming.
- Water mist sprays very fine droplets at high or low pressure. The droplets absorb heat quickly, turn to steam and push the oxygen away near the fire. It uses much less water than sprinklers and is safe for people, so it can be used in an engine room without evacuating it.
- Water spray (deluge or drencher) systems have open nozzles. When a section valve is opened, every nozzle in that section sprays at once. They protect car decks and other large spaces.
Water in pipes causes its own problems: corrosion, scale, bacteria and slime. That is why IMO now asks for water quality checks in sprinkler systems and for regular function tests of a sample of real sprinkler heads.
In detail
Automatic sprinklers (FSS Code chapter 8)
- Wet pipe systems, with small dry pipe sections only where needed; saunas have dry pipe systems with heads rated up to 140°C.
- Heads operate between 68°C and 79°C in accommodation and service spaces; in drying rooms they may be rated up to 30°C above the maximum deckhead temperature.
- Sections of not more than 200 heads; on passenger ships a section serves at most two decks and one main vertical zone. Each section has one stop valve, a test valve that simulates one head opening, and a pressure gauge.
- A pressure tank of at least twice the standing charge of fresh water, the charge being one minute of pump output, with a glass level gauge. An independent sprinkler pump starts automatically on pressure drop and covers at least 280 m² at 5 l/m²/min. A connection to the fire main through a lockable screw-down non-return valve.
- Alarms for every section at the bridge or continuously manned control station, with test switches, and a plan of sections at each indicating unit.
- Spare heads: 6 for fewer than 300 heads, 12 for 300 to 1,000, 24 for more than 1,000, for all types and ratings fitted.
- Equivalent sprinkler systems (often low-pressure water mist in accommodation) are approved under IMO resolution A.800(19), as revised.
Water mist and water spray in machinery spaces
Water-based systems equivalent to the fixed systems of SOLAS II-2/10 in machinery spaces of category A and cargo pump-rooms are approved under MSC/Circ.1165, as amended by MSC.1/Circ.1237, MSC.1/Circ.1269 and MSC.1/Circ.1386. The main conditions: manual release; proven fire extinction in full-scale tests; water supply for at least 30 minutes; main and emergency power with automatic change-over; a redundant means of pumping able to replace any single pump; a permanent sea inlet so the system can run on seawater; controls outside the protected space; and an alarm in the space and at a manned station when any section valve opens.
The local application system required by SOLAS II-2/10.5.6 is approved under MSC/Circ.913 (revised by MSC.1/Circ.1387). It must work with the engines running and the space manned; in unattended machinery spaces it must have automatic as well as manual release, so its detection and release logic is part of the system to be tested.
Ro-ro, vehicle and special category spaces
Fixed water-based systems for these spaces are approved under MSC.1/Circ.1430; for systems installed on or after 1 January 2024, use Rev.3. SOLAS II-2/20.6.1.2 requires a pressure gauge on the valve manifold, clear marking of the spaces served by each valve, operating and maintenance instructions in the valve room and enough drainage valves. Because large amounts of water on a car deck can capsize a ship, the scuppers and drainage arrangements are part of the system and must be kept clear.
Coming in for new ships: ro-ro passenger ships built on or after 1 January 2026 with weather decks for vehicles need fixed water monitors delivering at least 2.0 L/min per m² of the protected area, no monitor below 1,250 L/min, with nozzles at 5.0 L/min per m² for areas monitors cannot reach (FSS Code chapter 7, section 2.5, added by resolution MSC.555(108)).
Testing and inspection schedule (MSC.1/Circ.1432 as amended by MSC.1/Circ.1516)
| Interval | What |
|---|---|
| Weekly | Control panel indicators and alarms work; pump unit and fittings inspected; pump unit valves in position |
| Monthly | Control, pump unit and section valves in position; pressure tank water levels; automatic pump start tested; standby and air/gas pressure gauges in range; a sample of section valves flow-tested for alarm, chosen so all are tested within a year |
| Quarterly | Water quality in the header tank and pump unit assessed against the maker’s guidelines |
| Annual | Each section through its test valve; accessible components; high-pressure cylinders inspected and test dates checked; alarms; pump flow tests; antifreeze; cross-connections; relief valves; strainers; dry pipe sections blown through; emergency power change-over; all sprinklers visually inspected (especially saunas, spas, galleys, gyms, luggage areas); new obstructions; one section of each open-head water mist system flowed (all within 5 years); automatic heads function-tested to the flow chart, with water quality tests in each tested section |
| Five-yearly | Ro-ro deck deluge piping flushed, drained and purged with air; internal inspection of control and section valves; water quality tests in sections not tested in the last five years; batteries checked or renewed; new water quality baseline after any refill |
| Ten-yearly | Hydrostatic test and internal examination of gas and water pressure cylinders to flag guidelines or EN 1968:2002 + A1 |
The sprinkler head flow chart, step by step
MSC.1/Circ.1516 added a flow chart for testing automatic sprinkler heads and water mist nozzles. A type is each different maker’s model. A functional test shows the head opens and water flows; all tests are done at the system’s static (standby) pressure. The failure rate is the number failed divided by the number tested, times 100.
- System installed less than 5 years: test 2 random heads of each type. If one or more fail, the chart moves on to the 20-heads-per-type test in step 2.
- Installed 5 years or more: for each type, test 2 random heads per section in 10 sections (20 per type). Where both heads in a section fail, test 10 more heads in that section; if 2 or more of those fail, replace all heads in that section.
- A type with 3 or more failures out of 20 (15% or more) goes to extended testing. Case 1 (15% to 20%): 2 random heads per section, in all sections if fewer than 20, in 20 sections if 20 to 40, and in 50% of sections if more than 40. Case 2 (above 20%): 7 random heads in every section, unless the decision is taken to replace all heads of that type.
- After extended testing, a type failure rate above the chart’s limits means replacing all heads of that type (in the affected sections or throughout, as the chart sets out); otherwise the situation is monitored at the next annual survey.
Painted or visibly damaged heads are replaced and not counted in the sample. Use the spare heads, and replenish the spares.
What the rules say
- FSS Code chapter 8, paragraph 2.3.1.1, requires sprinklers in accommodation and service spaces to operate within 68°C to 79°C, and paragraph 2.3.1.2 sets the spare heads at 6, 12 or 24 depending on the number installed.2
- FSS Code chapter 8, paragraph 2.4.2, limits each sprinkler section to 200 heads, with one stop valve and a test valve for the section alarm near the stop valve.2
- FSS Code chapter 8, paragraph 2.4.1.2, requires special attention to the water quality specified by the manufacturer to prevent internal corrosion and clogging of sprinklers.2
- MSC.1/Circ.1432, paragraph 3.4 as amended by MSC.1/Circ.1516, says the quality of water in automatic sprinkler systems “is of particular importance” and that records of water quality should be kept on board.1
- MSC.1/Circ.1432, paragraph 5.4, calls for monthly testing of automatic pump starting and of a sample of section valves for flow and alarm, so that all valves are tested within one year.1
- MSC.1/Circ.1432, paragraph 7.5 as amended, calls for an annual visual inspection of all sprinklers and function tests of automatic sprinklers and water mist nozzles according to the flow chart, with painted or damaged heads replaced and not counted in the sample.1
- MSC.1/Circ.1432, paragraph 7.5.16, calls for at least one section of each open-head water mist system to be flow-tested each year, so that all sections are tested within five years.1
- MSC.1/Circ.1432, paragraph 10.2, calls for a hydrostatic test and internal examination of gas and water pressure cylinders every 10 years, to flag guidelines or EN 1968:2002 + A1.1
- MSC/Circ.1165, paragraphs 10 to 24, requires equivalent water-based systems for machinery spaces to have manual release, a 30-minute water supply, redundant pumping, main and emergency power, controls outside the space, and an alarm when any distribution valve opens.3
- SOLAS regulation II-2/10.5.6.4 requires the activation of any local application system to give a visual and distinct audible alarm in the protected space and at continuously manned stations, indicating the specific system activated.4
- FSS Code chapter 7, section 2.5, added by resolution MSC.555(108), requires fixed water monitors for vehicle weather decks on ro-ro passenger ships built on or after 1 January 2026, at a combined capacity of at least 2.0 L/min per m² and no less than 1,250 L/min per monitor.5
Flag and class notes
- Marshall Islands (Marine Notice 2-011-14, Rev. Aug/2025) requires the ten-yearly hydrostatic test and internal examination of gas and water pressure cylinders to EN 1968:2002 + A1 or equivalent RO requirements, and lists records of water quality in automatic sprinkler systems among the records to be kept on board.6
- Panama (Merchant Marine Circular MMC-281, October 2025) adopts the MSC.1/Circ.1516 amendments into its national rules, including the quarterly water quality assessment of the header tank and pump unit.7
- Hong Kong (Merchant Shipping Information Note 55/2023) applies MSC.1/Circ.1430/Rev.3 to fixed water-based systems for ro-ro and special category spaces installed on or after 1 January 2024.8
- Water mist and sprinkler systems are type approved; class surveyors check that the nozzle types and positions on board match the approval and that no new obstructions (ducts, cable trays, machinery) have been added in a refit. Ask the maker for the water quality limits for your system.1
Key numbers
| What | Value |
|---|---|
| Sprinkler operating temperature (accommodation) | 68°C to 79°C2 |
| Sauna heads (dry pipe) | Up to 140°C2 |
| Heads per section, maximum | 2002 |
| Spare heads | 6 (<300 heads), 12 (300-1,000), 24 (>1,000)2 |
| Sprinkler pump design area | 280 m² at 5 l/m²/min2 |
| Water mist water supply (machinery spaces) | At least 30 minutes3 |
| Section valve flow and alarm test | Monthly sample, all valves within a year1 |
| Open-head water mist sections flowed | One per year per system, all within 5 years1 |
| Basic test sample, system under 5 years | 2 heads per type1 |
| Basic test sample, system 5 years or older | 20 heads per type (2 in each of 10 sections)1 |
| Extended testing trigger | Failure rate of 15% or more (3 of 20)1 |
| Water quality check | Quarterly, plus with every function test1 |
| Cylinders hydrostatic test | Every 10 years (EN 1968:2002 + A1)1 |
| Ro-ro passenger weather deck monitors (new ships from 2026) | 2.0 L/min per m², at least 1,250 L/min per monitor5 |
What inspectors find
- Sprinkler heads painted over, damaged, or blocked by new ceilings, ducts or stored goods, especially after refits; MSC.1/Circ.1516 names saunas, spas, galleys, gyms and luggage areas as places to look first.1
- Section valves found closed or not locked, and pressure tanks with low water level or no air cushion.1
- No records of water quality, or water quality never tested although the system has been refilled.6
- In the 2012 Paris and Tokyo MOU fire safety campaign, the sprinkler section alarm failed its test in 2.1% of the inspections where the question applied.9
- Local application systems switched to manual only in an unattended engine room, or with detectors disconnected after false alarms.4
FAQ
Can the crew do the sprinkler head function tests?
The maintenance plan decides. MSC.1/Circ.1432 says competent crew members who have completed advanced fire-fighting training can do some work, but sampling, removing and refitting heads on a pressurised system is usually done by the maker or a service supplier, with the results given in a report.
What counts as a "type" of sprinkler head?
Each different manufacturer model. Two heads from the same maker but with different temperature ratings or response may be different models; check the part numbers on the heads and in the system documentation.
Our water mist system uses fresh water from a tank. Why must it have a sea inlet?
MSC/Circ.1165 paragraph 17 requires a permanent sea inlet so the system can run continuously on seawater once the fresh water is used up. After any seawater use, flush the system with fresh water.
Do we test the local application system by spraying the main engine?
Usually not with the engine running. Follow the maker’s procedure; tests normally prove detector inputs, release logic, alarms and valve operation, and the flow of water through a test line or a selected section with the area made safe.
Quiz6 questions
Sources
- 1
IMO MSC.1/Circ.1432, Revised guidelines for the maintenance and inspection of fire protection systems and appliances (31 May 2012), as amended by MSC.1/Circ.1516 (8 June 2015, new paragraph 6.5, revised paragraphs 3.4, 7.5 and 9.3 and the sprinkler test flow chart), annex, paragraphs 4.7, 5.4, 6.5, 7.5, 9.3 and 10.2 (consolidated copy annexed to Cayman Islands Shipping Notice 01/2014 Rev 2). https://www.cishipping.com/system/files/notices/documents/CISN%202014_01%20Rev%202%20with%20Annex.pdf
- 2
International Code for Fire Safety Systems (FSS Code), chapter 8, Automatic sprinkler, fire detection and fire alarm systems, paragraphs 2.1 to 2.5 (resolution MSC.98(73), as amended). https://wwwcdn.imo.org/localresources/en/KnowledgeCentre/IndexofIMOResolutions/MSCResolutions/MSC.98(73).pdf
- 3
IMO MSC/Circ.1165, Revised guidelines for the approval of equivalent water-based fire-extinguishing systems for machinery spaces and cargo pump-rooms (10 June 2005), annex, paragraphs 10 to 26; amended by MSC.1/Circ.1237, MSC.1/Circ.1269 and MSC.1/Circ.1386. https://www.register-iri.com/wp-content/uploads/MSC.1-Circ.1165.pdf
- 4
IMO Resolution MSC.99(73), revised SOLAS chapter II-2 (adopted 5 December 2000), regulation II-2/10.5.6, as amended by resolution MSC.338(91). https://wwwcdn.imo.org/localresources/en/KnowledgeCentre/IndexofIMOResolutions/MSCResolutions/MSC.99(73).pdf
- 5
IMO Resolution MSC.555(108), Amendments to the FSS Code (adopted 23 May 2024, in force 1 January 2026), annex, chapter 7, new section 2.5. https://wwwcdn.imo.org/localresources/en/KnowledgeCentre/IndexofIMOResolutions/MSCResolutions/MSC.555(108).pdf
- 6
Republic of the Marshall Islands Maritime Administrator, Marine Notice 2-011-14 (Rev. Aug/2025), sections 9 and 12. https://www.register-iri.com/wp-content/uploads/MN-2-011-14.pdf
- 7
Panama Maritime Authority, Merchant Marine Circular MMC-281 (October 2025), paragraphs 4.2.4 and 4.5.5. https://flagadmin.com/upload/userfiles/Panama/MMC-281-OCTOBER-2025-CM.pdf
- 8
Hong Kong Marine Department, Merchant Shipping Information Note 55/2023 (4 September 2023), on MSC.1/Circ.1430/Rev.3. https://www.mardep.gov.hk/en/msnote/pdf/msin2355.pdf
- 9
Tokyo MOU, Report of the 2012 Concentrated Inspection Campaign (CIC) on Fire Safety Systems (November 2013), section 3, question 7. https://www.tokyo-mou.org/wp/wp-content/uploads/Final-Tokyo-MOU-Report-FSS-CIC-public-web-site.pdf
Rules checked 20 October 2026. VSL Safety is not an approved training provider and doesn't issue certificates. These lessons don't replace STCW training, or the manufacturer's training and certification that service technicians need.
