Since we are working offshore and the ATM of pressure that comes with deep water would account for a catastrophic gas bubble at surface.
A small bubble at depth when it rises would EXPAND to huge proportions.
The talk has been that the cement was not set, gas came up through the cement and when it neared surface expanded to a huge FLASH.
The only thing that can be said for the missing men, is that it hit so hard and fast, they never knew what happened.
Prayers to all who work in and around a wellhead, whether it is on the surface of 5000 feet below the surface of water.
IT IS NATURE, it is something that man has tried to tame, control, collect and distribute.
As for the BOPS, it is easy to think it was the expendables that gave way, but from some investigations of BOP failure, many other things have to be considered. If the BOPS had seen a bunch of H2S on other jobs, the BOP may have been pitted (damaged internal or structurally) and wouldn’t have made it self apparent during a 7 minute HOLD test in a shop. That test looks for obvious leaks.
It will be interesting to find out:
Where the BOPS third party rentals? The last intrinsic test performed, and whether or not the BOPs had seen too much H2S?
Also will be curious as to the last time the rams had been replaced.
H2S can cause pitting, but with sea water already in play, I would assume the appropriate measures were taken into consideration. A more common issue with HS2 is embrittlment, but that is generally a pipe issue and would bake out between jobs.
I suspect (as noted by other posters) someone used the wrong O-ring. The doors on the BOP will open and close just a smidge with cycles of pressure and an improper ring (say a round one on a square door) will creep in and get “eaten” —— no loss of control until you have a catastrophic loss of control.