Lessons Learned: CO2 systems should be always maintained

UK MAIB, in its latest Safety Digest, discusses a CO2 gas release from the engine room’s fixed fire extinguishing system of a roro passenger ferry, highlighting that amongst the possible factors that caused the release was the fact that the service supplier overhauled the cylinder valves, instead of returning them back to the manufacturer and acquire new ones.

The Incident

The CO2 discharge alarm on a ro-ro passenger ferry alerted the engineers that there might be a potential release of CO2 gas from the engine room’s fixed fire extinguishing system.

An engineer when approaching the CO2 room, heard a loud hissing noise. He opened the door and found that one of the cylinder outlets had frosted up around the junction of the flexible outlet hose and the main gas manifold, and a white cloud was forming in the space.

The main control valve to the engine room remained closed and no gas had been released into the engine room.

In light of the incident the crew informed the service supplier, who was responsible for maintaining the CO2 systems, and arrived on the vessel. Donning a breathing apparatus, he entered the CO2 room and disconnected the flexible outlet hoses from all 26 cylinders.

All the cylinders were subsequently landed ashore and weighed. It was established that all but the two master cylinders had discharged either partially or completely.

Probable Causes

1. The main manifold had been pressurised, as a result of a leaking discharge valve on one of the cylinders.
2. When the pressure in the main manifold rose above 4.5 bar the release mechanism was activated, causing the entire system to discharge.
3. The main manifold pressure alarm, which should have alerted the crew at a very early stage to the leakage into the manifold, was damaged and did not function as intended.
4. The manifold was not fitted with any vent valves that would release any minor gas leakage into the manifold before it led to a build-up of pressure, although these were available from the cylinder valve manufacturer.
5. It’s common that service suppliers overhaul the cylinder valves, despite the manufacturer’s instructions requiring all cylinder valves to be returned to them for refurbishment.
6. During servicing the service supplier would typically apply service air from the ship’s compressed air reservoirs to the manifold instead of using dry air or nitrogen as recommended.

Lessons Learned