Good insights. Thanks. What puzzles me is that atmospheric pressure water tanks are open to the atmosphere at top (right?). The openings are covered with a screen to keep out debris and animals. So one would think that would prevent an explosive regime from being reached, wouldn’t it? Especially because most of the resulting hydrocarbon gases are less dense than air.
It’s puzzling why a side seam didn’t fail first, but all the bolts or welds at the connection between the sidewalls and floor let go simultaneously. That is what suggested to me corrosion problems at the floor/sidewall junction.