The Mobil Pegasus exploded in the South Atlantic on 21st June 1973
whilst changing ballast.
1C was being loaded with clean ballast.
The pipeline ran through the double bottom
and entered 1C facing upwards (rather than downwards onto the bottom plates).
Although there were baffles, the tremendous in-rush of water
(and consequential static) when the Chief Mate opened the 1C valve
must have ignited the explosive mixture in the tank.
The plating peeled backwards like a sardine can
virtually the width of the ship folding back upon the main deck.
The hole in the deck extended from the centre castle to the break of the focsle.
Fortunately, although we had many injured,
there were no deaths mainly
because of a fine Polish Doctor on a communist polish cargo ship
that came to our help -- long story.
The fire was extinguished by flooding the forward tanks.
Vessel limped back to Dakar for temporary repairs,
and thence to Lisbon escorted by tug at 5 knots.
Mobil Oil had carried out tests a year before (on the Mobil Pegasus!)
and knew about the dangers of static -
unfortunately they failed to tell the mariners at sea.
I know this because by luck I came upon (2 years ago)
the American who carried out the tests.