A scaffolder fell 39m (130ft) from an oil rig docked at Invergordon after he stepped on to corroded grating, a fatal accident inquiry (FAI) has heard.
Lewis MacDonald, 35, was working on the Ocean Princess when he died on 28 November 2008.
Ch Insp Matthew Reiss, of Northern Constabulary, told the inquiry the grating, which had wooden boards over it, had given way.
The FAI before Sheriff David Sutherland at Tain Sheriff Court continues.
Mr MacDonald, of Milnafua, Alness, was part of a squad helping to refurbish the semi-submersible docked at the harbour in the Cromarty Firth.
The grating had been exposed after a tool shed, which had been sitting on top of it since 1997, was dismantled.
A scaffolding barrier was set up around the corroded grating, while wooden planks were placed on the majority of the exposed patch.
The court heard that Mr MacDonald had been in the process of adjusting scaffolding when he stepped on to an uncovered part of the grating.
He hit a metal cross beam on his fall into the sea. Rescuers went to his aid and pulled him from the water.
Ch Insp Reiss, the first officer on scene, said: "He was on the quay side underneath the rig.
"Once I realised there was nothing I could do for Mr MacDonald I cordoned off the scene at the top of the rig."
HSE inspector John Sutherland said he would not have expected an experienced scaffolder such as Mr MacDonald to "have exposed himself to the risk of falling".
He said the workman had gone into an area he considered to have been adequately made safe by barriers.
The inquiry continues.