The 41-year-old seafarer had gone into the hold of the 4,200-dwt Lady Irina (built 1997) on Sunday, local media said.
Four colleagues went to look for him after he didn’t come back and they were also affected by gas.
Police said two of the four were placed in a pressure chamber in hospital, but all four recovered.
The vessel is operated by Wijnne & Barends Cargadoors of the Netherlands.
