Police have been questioning the Russian master of a container ship over the North Sea collision, with salvors planning to board the second stricken vessel to assess the damage.
The 59-year-old mariner was in custody in East Yorkshire after being arrested on suspicion of gross negligence manslaughter over the crash, which left a member of his crew feared dead.
The vessel he was captaining, the Solong, hit a US-flagged tanker, Stena Immaculate, carrying jet fuel for the American military. The Stena Immaculate was anchored while waiting for space at a port in the Humber after travelling from the Peloponnese region of Greece.
The Maritime and Coastguard Agency (MCA) said on Wednesday that fires onboard the Solong had “greatly reduced” and that it was being held in a safe position off the coast of Yorkshire, having broken free of the Stena Immaculate on Monday night.
Coastguard officials had hoped to board the Stena Immaculate to carry out an initial damage assessment on Wednesday before salvors could begin a full review of the wreckage.
The Solong was sailing from Grangemouth in Scotland to Rotterdam in the Netherlands at a speed of about 16 knots, equivalent to 18mph, when it collided with the tanker.
Both vessels caught fire after several explosions. Thirty-six crew were rescued, including Americans from the Stena Immaculate and the Russian and Filipino nationals that made up the Solong’s crew.
Investigators said nothing was being ruled out, but added there was nothing at this point to suggest there was Russian state involvement in the incident.
It was initially feared the Solong, a container ship with a Portuguese flag, was carrying the highly toxic chemical sodium cyanide but its owner, the Hamburg-based maritime firm Ernst Russ, said four containers that had previously held the substance were empty.
Air quality sampling carried out onshore had shown no toxins and modelling from the Met Office indicated no threat to the public, HM Coastguard said.
Though the Solong drifted at least 2 miles south of the collision, it Solong is no longer expected to sink and is anchored with support from a tugboat. The Stena Immaculate is also being held in place by tugboats.
Some of the jet fuel that was on the tanker, equivalent to 220,000 barrels in total, will have burned in what was described as a “massive fireball” but it remains likely some has spilled into the sea, causing possible environmental damage.
On Tuesday evening, the assistant chief coastguard John Craig said the fire on the Stena Immaculate, which continued to burn throughout the second day, had “greatly reduced”.
He said: “A comprehensive counter-pollution response is in place and HM Coastguard continues to make preparations for any pollution that may occur as a result of the damage to the vessels.
“We continue to engage actively with Humberside police, salvors, the port authorities and other agencies to protect the public and the environment as far as possible while continuing to respond to the developing situation.”
While it will take the Marine Accident Investigation Branch some time to fully investigate the causes of the crash, Humberside police launched a parallel investigation into the mariner’s suspected death.
On Tuesday Ernst Russ confirmed to the Guardian that the ship’s master had been detained by Humberside police, adding: “The master and our entire team are actively assisting with the investigations. Out of respect for the investigation and all involved we will not comment further at this time.”
The senior investigating officer, DCS Craig Nicholson, said on Tuesday: “Extensive work has already been carried out, and we are working closely with our partners to understand what happened, and to provide support to all of those affected.
“The man arrested remains in custody at this time whilst inquiries are under way, and we continue speaking with all those involved to establish the full circumstances of the incident.”
