UN’s Yemeni oil tanker operation: What you need to know

A UN-led operation years in the making to prevent a large-scale oil spill from occurring off Yemen’s Red Sea coast has made major gains.

The replacement vessel Nautica sailed from Djibouti, arriving at Yemen’s Hodeidah port Saturday evening, the vessel to which over 1.1 million barrels of oil will be transferred from the decaying FSO Safer supertanker.

The operation, the first of its kind, is a risky one – but the potential leaking of the remaining oil in the deteriorating tanker that the Yemeni government purchased in the 1980s is even more so.

Observers have worried for years that the FSO Safer could crack or explode; The ensuing oil spill would have the potential to wipe out one of the world’s largest marine ecosystems.

Here’s what you need to know about the operation to prevent what could be “one of the worst oil spills in history” according to the UN.

How long has the tanker been stranded and why?

The 47-year-old supertanker was left abandoned and has been out of service since the civil war broke out in Yemen eight years ago.

The FSO Safer is anchored near the Ras Isa oil terminal controlled by Yemen’s Houthi movement who in 2015 seized large parts of the country.

Why does the oil have to be transferred?

The tanker has not been properly maintained since it was left abandoned and is situated in an area littered with mines, according to Mohammed Mudawi from United Nations Development Programme (UNDP) Yemen, whose team has been working to prevent the build-up of flammable gases.

“We have many concerns that it can explode because of the gases,” Mudawi told Al Jazeera.

The supertanker could also fall apart since the lack of maintenance has weakened its structural integrity.

What damage could an oil spill do?

According to the UN, a major spill would destroy coral, mangroves and other sea life; expose millions of people to highly polluted air; devastate fishing communities; force nearby ports to close; and disrupt shipping through the Suez Canal.

“A major spill from the vessel would result in an environmental and humanitarian catastrophe,” the UN’s Yemen team said in a statement.

The cost of the clean-up alone is estimated at $20bn.

“A spill would be a disaster. It would spread across the Red Sea, all the way to the Gulf of Aden, disrupting movement through the Suez Canal, and wiping out one of the world’s richest marine ecosystems,” said Al Jazeera’s Hashem Ahelbarra, reporting from Hodeidah.

As it stands, the likelihood of a massive oil spill is high and could potentially have an impact greater than one of the largest oil spills in history, the 1989 Exxon Valdez disaster, since the FSO Safer carries four times the amount of oil, according to the UN.

How would the oil transfer take place?

The oil from the supertanker will be pumped into the replacement vessel Nautica, a ship-to-ship transfer that is expected to take two weeks, according to the UN.

Once the oil is off-loaded, the delivery and instalment of a catenary anchor leg mooring (CALM) buoy will take place, the UN said.

The buoy will then be secured to the seabed, which in turn will be used to secure the replacement vessel, a process that must be completed by September, the international body adds.

A technical support vessel from the Dutch-based company Boskalis/SMITis would be ready to step in should any oil leaks occur during the operation.

What would happen to the oil once it’s transferred?

The Houthis and Yemen’s internationally-recognised government backed by a Saudi-led coalition are in dispute over who owns the ship and who has the right to sell the oil once it is unloaded.

As a result, the salvage operation cannot be paid for by the sale of the oil because it is not clear who owns it, the UN said.

The operation has an estimated budget of $148m, with the UN having raised $118m so far.

Zaid al-Wushali, from the FSO Safer committee, hopes that Yemen’s oil exports would continue following the operation.

“Oil is a wealth that belongs to all of Yemen,” he told Al Jazeera.