In February 2017 the crew of the passenger cruise ship Emerald Princess were re-pressurising the gas cylinders after maintenance, when the cylinder burst below its normal operating pressure, causing the death of a nearby crew member. The cylinder had been weakened by corrosion. The inquiry report highlights a lack of global minimum standards for inspection, testing and rejecting pressure cylinders for stored energy systems on lifeboat launching installations – a system common on cruise ships.
Executive summary
On 9 February 2017, the crew of the Bermuda-flagged passenger ship Emerald Princess were conducting maintenance on one of the lifeboat launching systems while the ship was berthed at Port Chalmers, Dunedin.
The maintenance was completed and the crew were restoring pressure to a bank of high-pressure nitrogen-gas cylinders that formed part of the launching davit ‘stored energy’ system. One of the nitrogen bottles burst, fatally injuring a crew member who was standing close by.
The Transport Accident Investigation Commission (Commission) found that the nitrogen cylinder burst at below its normal working pressure because severe external corrosion had reduced the wall thickness to about 30% of its original thickness.
The failed nitrogen cylinder and several other pressure cylinders within the stored energy system, despite having been surveyed about two weeks earlier, were not fit for purpose and should not have been left in service.
The Commission also found that there is an urgent need for consistent and proper standards to be developed at a global level for maintaining, inspecting, testing and, where necessary, replacing high-pressure cylinders associated with stored energy systems on board ships.
The operator took a number of immediate safety actions to prevent a recurrence of the accident on any of its ships.
The Commission issued an interim report with early recommendations to the equipment manufacturer, the International Society of Classification Societies, the Cruise Lines International Association and Maritime New Zealand to alert their members and surveyors as appropriate to the circumstances of the accident and to have the condition of similar installations checked.
The Commission made two additional recommendations: one for the manufacturer to improve training for its surveyors; and one for Maritime New Zealand to raise, through the appropriate International Maritime Organization safety committee for its consideration, the implications for maritime safety of not having adequate minimum standards for the inspection, testing and rejection of pressure vessels that are part of stored energy systems.
A key lesson arising from this inquiry is:
- any sign of corrosion on high-pressure cylinders should be fully investigated by a person competent in examining high-pressure cylinders before any remedial work is undertaken and the cylinders are allowed back into service.
Related Recommendations
The nitrogen cylinders that formed part of the stored energy system on board the Emerald Princess were stowed in a harsh marine environment and had significant external corrosion. The nitrogen cylinders were inspected annually by the manufacturer’s authorised technician. The most recent inspection was two weeks prior to the accident. On each occasion the cylinders were judged to be in satisfactory working condition.
The cylinder failed at below its normal working pressure because severe external corrosion had reduced the wall thickness from 4.81 mm to 1.45 mm (about 30% of its original thickness). The failed nitrogen cylinder and several other pressure cylinders within the stored energy system were not fit for purpose and should not have been in service. There is an urgent need for consistent and proper standards to be developed at a global level for maintaining, inspecting, testing and, where necessary, replacing high-pressure cylinders associated with stored energy systems on board ships.
On 10 April 2017 the Commission recommended to the International Association of Classification Societies that it inform all of its members about the circumstances of this accident and advise them to alert their surveyors to pay special attention to any corroded nitrogen cylinders or other pressure vessels when conducting their Class or Flag State surveys, particularly when inspecting pressure vessels stored in an open marine environment.
On 10 April 2017 the Commission recommended to the Director of Maritime New Zealand that he inform all New Zealand surveyors and port state control officers about the circumstances of this accident and advise them to pay special attention to any corroded nitrogen cylinders or other pressure vessels when conducting their Class or Flag State surveys, particularly when inspecting pressure vessels stored in an open marine environment.
On 10 April 2017 the Commission recommended to the Cruise Lines International Association that as a matter of urgency it contact members, informing them about the circumstances of this accident and warning them to have the systems inspected immediately by a competent person. Any corroded nitrogen cylinders or other associated pressure vessels should be removed for further assessment.
On 10 April 2017 the Commission recommended to the manufacturer that, as a matter of urgency, it contact all known ship owners that have the same or similar emergency launching and recovery systems installed on their vessels, informing them about the circumstances of this accident, and advising them to have the systems inspected immediately by a competent person to check whether the nitrogen cylinders and other pressure vessels associated with the systems are fit for purpose. Any nitrogen cylinders deemed unfit due to corrosion should be removed for further assessment