I think the oil rig explosion will be found to have been a surge of highly pressurized gas that entered the pipeline (remember the depths that we're talking about) and was larger than the equipment could handle.
Other than never being 100% certain of what the subsurface looks like, I'm betting that this took the workers by surprise. I think they were following procedurs by the book, but they got hit by that that 0.001% uncertainty that still exists when don't know for sure what it looks like under the surface.
-PJ
A bit like that mine explosion that killed about 30 people. Inherently dangerous, like a soldier going to war or a surgeon operating on someone’s heart, or a ship moving ay high speed among icebergs. Every great endeavor sometimes ends in failure. Our task is not to lose heart.