Green patina on mist nozzles is a sign of corrosion, warns The Nautical Institute in a new Mars Report. In the case described, the malfunctioning of the mist nozzles was uncovered during a US Coast Guard inspection.
The Nautical Institute gathers reports of maritime accidents and near-misses. It then publishes these so-called Mars (Mariners’ Alerting and Reporting Scheme) Reports (anonymously) to prevent other accidents from happening. This is one of these reports.
A passenger vessel was undergoing a US Coast Guard inspection, including a test of the high-pressure water mist nozzles (part of the HI-FOG fire suppression system). The high-pressure water mist nozzles are designed to hold the standard line pressure of 25 bar (363 PSI).
When the glass bulb thermal actuator reaches a certain temperature, it breaks, activating the release mechanism which allows water to flow through the nozzle at the standing pressure. The system then senses the drop in pressure and automatically activates the high pressure pumps, increasing the pressure to 140 bar (2,031 PSI). This increased pressure is required for the system to achieve an effective release of water as a mist.
Due to past failures, the manufacturer (Marioff) released a Service Bulletin (001/2012) recommending that if a nozzle fails to release at the standing pressure of 25 bar after the glass bulb is broken, the high-pressure pumps must be manually energised to raise the pressure to 140 bar. This should activate the release mechanism, allowing water to flow through the nozzle. During the examination this recommended action was taken, but did not activate the release mechanism of the nozzles as expected.
Upon closer inspection, it was found that the high-pressure water mist nozzles had accumulations of green patina, a sign of corrosion, which rendered them unable to release water after the glass bulb broke, even with 140 bar pressure.
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Advice from The Nautical Institute
- Does your vessel have high-pressure water mist nozzles? Check for green patina!
- Sprinklers at the highest risk of corrosion include sprinklers more than ten years old and those located in high moisture and corrosive atmospheres. Areas of high moisture could include outer decks, spas, pool areas, galleys, or even normal passenger and crew areas close to external doors.
- Contact the manufacturer if any signs of green patina build-up are observed on high-pressure water mist nozzles. Consider replacing the affected nozzles.
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Mars Reports
This accident was covered in the Mars Reports, originally published as Mars 202545. A selection of the Mars Reports are also published in the SWZ|Maritime magazine. The Nautical Institute compiles these reports to help prevent maritime accidents. That is why they are also published (in full) on SWZ|Maritime’s website.
More reports are needed to keep the scheme interesting and informative. All reports are read only by the Mars coordinator and are treated in the strictest confidence. To submit a report, please use the Mars report form.
Picture by The Nautical Institute.
