The Marine Accident Investigation Branch (MAIB), has issued a safety bulletin to highlight urgent safety lessons that have arisen in the early stages of its investigation into the mooring line failure on board LNG tanker, Zarga.
Zarga was working alongside South Hook LNG terminal, Milford Haven, when the mooring line failure resulted in serious injury to a deck officer on 2nd March 2015. The mooring line parted during a berthing operation and resulted in the deck officer being struck and obtaining severe head trauma.
Following the accident, the MAIB commissioned a series of tests and trials designed to measure the elongation and snap-back characteristics of the mooring lines used on board Zarga. When sections of the UHMPE rope were loaded to the point of failure the average maximum elongation was about two percent and minimal snap-back was observed.
When the trial was repeated with the Euroflex tail2 attached the elongation was significantly increased. Similar to the accident, it was the UHMPE section of the line that parted, and the failed end that was attached to the tail snapped back over 15m in less than one second. The other end of the UHMPE rope did not snap back.
MAIB suggested to following safety lessons:
• When connecting synthetic tails to UHMPE, HMPE and wire mooring lines, the energy introduced due to the elasticity of the tails can significantly increase the snap-back hazard.
• Elongation is proportional to the length of tail. Increasing the length of the tail will increase the amount of elongation and hence the amount of energy that can be stored in the line when under load.
• Ship owners/operators should ensure that the type of lines and tails used for mooring lines are suitable for the task and that the dangers of snap-back are fully considered.
• Mooring teams should be aware of the potential for snap-back in all types of mooring line, and the probable areas on the mooring deck that are not safe when lines are under load.
• Mooring lines led around roller pedestals and fairleads can lead to potentially complex snap-back zones. Ship operators and masters should conduct their own risk assessments to ensure potential snap-back zones are identified, and are reviewed at regular intervals.
• Notwithstanding the ongoing investigation into the nature of the failure of Zarga’s spring line, where doubt exists on the continued use of a mooring line, the vessel operator should obtain guidance from the rope manufacturer on the conduct of detailed line inspections.
The causes and contributing factors of Zarga’s mooring line failure are subject to an ongoing investigation and will be discussed in a full investigation report by the MAIB.
In the meantime, click to read the Zarga safety bulletin.