I've never sailed on these types. There are some very strict procedures
that must be followed when loading/discharging these ship.
If you look at a number of examples of tanker explosions (barring war)
you'll see most occur during tank cleaning, gas freeing, repairs.
When VLCC's and ULCC's first came into existence there were a number of
explosions during tank cleaning. It was found that due to the size of the
tanks, when cleaning a condition much like a thunderstorm was created in
the tanks and when the oxygen gas mixture got correct.....boom. Hence the
reason for IG (inert gas) and COW (crude oil washing).

I hear offloading an LNG ship is the most worrisome time.

Scotty