On 23 August 2011, a shore-based service engineer was seriously injured on board the tug SD Nimble when six cylinders of carbon dioxide were accidentally discharged shortly after the tug had slipped from her berth in Her Majesty’s naval base in Faslane, Scotland.
The engineer was testing components of the vessel’s fixed carbon dioxide fire extinguishing system in the carbon dioxide cylinder room. The accidental discharge of carbon dioxide caused a depletion of oxygen levels in the cylinder room and aft hold causing the engineer to quickly lose consciousness. The tug was immediately manoeuvred back alongside and the service engineer was quickly recovered onto the open deck, where cardio pulmonary resuscitation was started. The engineer was subsequently transferred by helicopter to the Southern General Hospital in Glasgow where, following a long period of recuperation and therapy, he made a good recovery.
The findings of the MAIB investigation included:
- The release of the carbon dioxide occurred because the pilot lines from the system’s control cabinet had not been isolated.
- The failure to disconnect the pilot lines was likely to have been a mistake resulting from an incorrect plan of action rather than a mis-identification of the system’scomponents.
- The service engineer’s training and the monitoring of his performance were ineffective in some areas.
- The tug’s crew and the service engineers worked in isolation, which resulted in the service engineers entering a potentially dangerous space and, concurrently, the vessel sailing with her main machinery space fixed fire extinguishing system inoperable.
CO2 Control Station
CO2 Cylinder Room after the Accident
A recommendation has been made to Lloyd’s Register aimed at ensuring that, in consultation with ships’ crew, service suppliers agree and implement safe systems of work prior to commencing work on board vessels. A recommendation has also been made to Ocean Engineering (Fire) Limited, which is intended to improve the monitoring and safety of its engineers.
Source: MAIB
Officer of the Watch 
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