At the end of a fatal accident inquiry into his death yesterday, Sheriff Annella Cowan said the medical evidence led during the hearing was nothing more than speculative.
She said it had been impossible for her to determine the cause of death any further than simply “death while saturation diving”.
Last night, Mr Robinson’s mother Carol said the family were “stunned” by the determination.
She said they had waited “two long years” to find out why her 33-year-old son had died and said that the outcome of the inquiry had left most of their questions unanswered.
Mrs Robinson said that it was too early for the family to decide on their next steps, but they would be discussing how to proceed.
She said: “The whole process, as you can imagine, has been deeply upsetting for all involved. We have never had to go through this process before and we hope we never have to again.
“What we really wanted to achieve was to find out what really happened to Russell. The information that has came to light has been a surprise to all of us.”
In her determination, Sheriff Cowan said she was confident that none of the equipment or the actions of Mr Robinson’s colleagues had contributed to his death.
She said: “It can now, in my view, safely be said that no part of the equipment; the saturation diving system; the habitation chamber; the bell; the umbilical; communications; air supply or the operation or configuration of any of these caused Mr Robinson’s death.
Last night a spokesman for Premier Oil said the firm was disappointed that the findings could not be more conclusive.
He said: “The thoughts of everyone at Premier Oil are very much with the family of Russell Robinson. In addition, we must pay tribute to Russell’s colleagues who fought tirelessly to help him yet, sadly, were unsuccessful.
“Naturally, we are disappointed that the findings of the inquiry could not be conclusive in determining what caused this tragedy, despite exhaustive investigations by all parties.”