Plans to put a salvage team on board an oil rig grounded on the Western Isles have been called off due to safety fears.
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 Isle of Lewis 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 the Alp Forward during towing from Norway to Malta and the weather prevented the line being reconnected.
A Marine Accident Investigation Branch investigation has begun into the loss of tow and grounding.
The Maritime and Coastguard Agency (MCA) said on Friday plans to put an eight-strong salvage team on board were called off as conditions prevented safely winching down.
The agency said it is impossible to board the rig by sea and is looking at bringing in additional air assets.
The team had been expected to conduct a further damage assessment after an initial inspection on Wednesday found half the rig’s four fuel tanks had been damaged. They were also due to
examine the emergency generator to establish what power is available.
A Maritime and Coastguard Agency spokeswoman said: “Salvors will determine the quantity of diesel remaining in those tanks during the course of the salvage operation.
“Diesel is a light and non-persistent oil which presents much lower environmental risks than heavy black crude oil.”
Hugh Shaw, the Secretary of State’s representative for maritime salvage and intervention, said: “There needs to be a comprehensive assessment of the state of the rig before a salvage plan can be
drawn up and put it into place.”
He 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, telling BBC Radio Four an air search of the coastline found “no trace of oil”.
A “low level” of pollution was detected by tests on Monday, Western Isles Council said, but daily shoreline inspections by the Scottish Environment Protection Agency have indicated no visible sign of pollution.
No-one was on board the rig when it grounded at Dalmore beach near Carloway.
People are being urged to stay away from the beach as teams continue to work and a temporary 300-metre (980ft) exclusion zone has been set up at sea.
Environmental groups have raised concerns while it is expected to take “some time” to refloat the rig as it came ashore at high tide with a storm surge.
Scotland’s Environment Secretary Roseanna Cunningham said serious questions need to be asked as to why the rig was being towed during severe weather and Deputy First Minister John Swinney had raised the point with the UK Government.