The ship was a CTL, and scrapped.
A French source agrees six killed,
but says 3 were refinery people.
Inert gas would almost certainly have made a big difference.
She may have also been doing the post discharge cargo survey,
in which case at least some of the ullage lids would have been open.
This is consistent with the French report
which says half the casualties were refinery people,
maybe the cargo surveyors?