The last person to leave Total’s Elgin platform after the leak was discovered said he had difficult decisions to make when the alarm was raised.
Offshore installation manager William Andrew Cardno was one of 19 men who stayed on board the stricken installation when it started leaking on March 25.
The rest of the 238 workers were evacuated immediately.
Mr Cardno said: “Even though we train for this, and we train regularly with drills every week, I never thought this would happen.
“When the first alarm was sounded we had the helicopter on-scene within one hour.
“And within an hour after that we had 107 people evacuated. An hour after that we had the full 220 people evacuated.
“We deliberately kept 19 people on board the platform to evaluate the situation and to see if there was anything we could do and really to maintain the systems.
“We knew once we turned the key to switch everything off all that was lost. That information was invaluable in trying to determine what the cause of the incident was.
“The hardest decision was when we had 19 people on board, we had to make a call about whether we had to go or whether we could stay.
“If we had any escalation at all on the platform we were absolutely confident we could have been off the platform in five minutes by lifeboat.
“We all practiced our lifeboat drill and we checked the lifeboat and strapped ourselves into it. The weather was good, the sea state was calm. It wasn’t an unacceptable risk to go by boat.
“I think this demonstrated that our procedures are good and our process is good.
“Although we never want these things to happen, when it does happen this clearly demonstrates that the safety of the people is our paramount priority.”
Total announced on Monday that it was facing a bill of nearly £350million to halt the gas leak.
And the French firm said the emergency shutdown was costing nearly $1.5million (£940,000) a day.
That is likely to rise by another $1.5million a day when work to drill the two relief wells begins.
At one point, the leak wiped more than £5billion off Total’s share price.