A DECK officer was seriously injured on a tanker at South Hook LNG after a mooring line failed according to the Marine Accident Investigation Branch (MAIB).

The MAIB has today issued a safety bulletin for all vessels following the incident in March which resulted in a man being struck by a mooring line that broke during a berthing operation at the Milford Haven LNG terminal causing severe head injuries.

He was working on the Zarga tanker which had been declared “all fast” alongside the terminal around 40 minutes before the accident and the attending tugs had left.

Gusty winds moved the vessel out of position while the mooring teams fitted chafing guards to the line and crew were tasked with tensing the “forward spring lines to warp Zarga back into the correct position”.

One of the lines parted from the winch and “the section of the line between the break and the port-shoulder roller fairlead struck the officer in charge on his head as it whipped back before going overboard through the fairlead”.

The MAIB is continuing to investigate the incident, with a full investigation report due to be prepared, but its initial findings are linked to ‘elongation and snap-back’ of the mooring lines.

It found that snap-back zones had not been marked on the Zarga’s mooring decks although the danger had been identified in the vessel’s risk assessments.

Elongation of lines introduce stored energy which can caused a broken line to recoil back towards its anchor point at high speed – referred to as snap-back.

Wire and high modulus synthetic lines have low elasticity and therefore low snap-back when they fail but it can make them “prone to failure under peak dynamic loading.

The preliminary MAIB report states: “On board Zarga, 11m tails were originally fitted to reduce peak dynamic loading, but these were replaced with 22m tails after peak dynamic loads were experienced that had led to a series of line failures. However, the 22m tails had much greater elasticity and this, and the routeing of the line, introduced a significant snap-back hazard to the outer section of the failed UHMPE mooring line.

“Because UHMPE mooring lines were fitted, the perception among members of the crew was that, in the event of a mooring line failure under load, the ends of a parted line would simply fall to the deck. In this case, the inboard section of the failed line recoiled a short distance towards the base of the winch.”

Tests were carried out following the accident to measure the elongation and snap-back of the mooring lines on the Zarga.

A number of safety lessons have been issues including reminding ship owners/operators that types 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 nap-back in all types of mooring line, and the probable areas on the mooring deck that are not safe when lines are under load and ship operators and masters should conduct their own risk assessments to ensure potential snap-back zones are identified, and are reviewed at regular intervals.