A salvage team was last night expected to spend the night on the grounded oil rig on Lewis after finding a safe access in difficult weather conditions.
The Transocean Winner rig was carrying 280 tonnes of diesel – more than 300,000 litres – when it was blown ashore in severe weather conditions on the western side of the island early on Monday.
The rig is believed to have leaked more than 50,000 litres of fuel, most of which is thought to have evaporated.
The semi-submersible installation detached from its tug during towing from Norway to Malta. Bad weather has meant the salvage team has only briefly been able to board for checks but teams used sea ropes to partially climb the structure on Saturday.
Rope access technicians have now created a safe alternative access after the prevailing weather made it too difficult to winch the team down to the installation. A team of eight salvors will assess the rig and make it habitable so that they can remain on it overnight.
The Maritime and Coastguard Agency said: “The team from Transocean and Smit will look at the diesel oil tanks, looking at how they might start procedures to transfer any fuel to other unbreached tanks within the rig so that it will be in a safe location well above the waterline, before any operation to refloat the rig commences. There’s also work going on in close proximity to the Transocean Winner to carry out a multi-beam survey looking to identify the safest route to move it when the time comes.
“An additional aircraft is going to be brought in to help with the work.
“An exclusion zone of 300 metres remains in place around the rig covering the sea and the air, which means no drones will be permitted in the area.” Hugh Shaw, the secretary of state’s representative for maritime salvage and intervention, said the “worst case scenario” is that about 52 tonnes, more than 50,000 litres, of oil has leaked into the environment. However, no oil has been seen on the surface of the sea and Mr Shaw said most of the escaped diesel would have evaporated.