In a previous post, we discussed JL Daeschler’s comments suggesting that the emergency disconnect sequence (EDS) may have actuated the shear ram, but that the sequence aborted when the ram did not close fully. Another knowledgeable commenter, while requesting not to be named, noted that:
Whether the EDS-functions terminated before the sequence was completed is clearly a relevant question.
I agree and believe this possibility may have been dismissed without being fully considered. The DNV report claims that the EDS sequence never actually initiated, probably because of a loss of communication with the stack after the initial explosion. As evidence, the report offers the following:
There is an account of lights flashing, indicating that the EDS function had initiated. There are no accounts of any specific lights going steady, which would have indicated a function had been completed and confirmed by the subsea control pods.
Comment: Perhaps no light stopped flashing because the first step in the sequence, BSR actuation, was not concluded (i.e. the BSR never fully closed).
Reviewed ROV video indicated no evidence that the sequence had initiated; the LMRP remained latched to the BOP, the Blue and Yellow Control Pod stingers were not retracted.
Comment: This only tells us that the sequence terminated prior to unlatching he LMRP and retracting the pod stingers. It says nothing about the timing of the BSR closure.
Note that pages 166-167 of the DNV report indicate that the EDS was manually functioned (at the test facility) via surface control and that it functioned as intended.
The report also confirms that the accumulators were functional:
HP Shear Close, EDS, AMF/Deadman and Autoshear have a common reliance on the accumulator bottles (8 x 80 gallon) located on the BOP. Testing of these accumulators determined that they functioned as intended in the as-received condition.
The report goes on to say:
This is further indication the BSR’s were activated either by the Authoshear or possibly the AMF/Deadman functions. No further failure cause analysis was performed.
Comment: So why was the EDS ruled out as the trigger for the BSR activation? Also, if the shear ram was activated by the AMF, why did that sequence terminate after the ram closed (partly)?
Comment on the riser disconnect: While closure of the BSR is a critical first step in the EDS or AMF sequence, riser disconnect, which has received very little attention, is equally important. To prevent flow, you want the well sealed before you disconnect the riser and the column of drilling fluid contained within. However when an EDS is activated, there is a good chance that the well may already have started to flow. Under those circumstances, you need to quickly disconnect the riser so the workers can be removed from the threat. In the case of the Deepwater Horizon, the failure of the riser to disconnect is as significant as the failure of the BSR to seal the well. Although the EDS may have been activated too late to save the workers who lost their lives, they would likely have been safe if the rig had been disconnected from the well prior to the initial surge.
Bud's Offshore Energy (BOE) 