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DNV’s forensic examination found that the main failure of the Deepwater
Horizon BOP stack was caused by a portion of the drill pipe being trapped
outside of the blind shear ram cutting surfaces, which prevented the blind shear
rams from fully closing and sealing. DNV was able to reconstruct the segments
of recovered pipe through analysis of the segments of pipe and tool joints that
were located throughout the BOP and riser, including analysis of wear patterns,
drill pipe dimensions, damage and deformation markings, sheared ends of
recovered drill pipe, and physical differences between the two recovered joints of
drill pipe. DNV also determined that a tool joint had been located in the upper
annular while flow was present. DNV also noted the as‐received condition of
many BOP stack components, i.e., blue and yellow pod battery voltages and
various ram positions. DNV’s report is included at Appendix D.

1. Sequence of Events Related to the Blind Shear Rams

There are two possible scenarios for how the blind shear rams were
activated and closed: (1) the autoshear circuit was activated on April 22, by
cutting the poppet valve between the LMRP and lower BOP stack; or (2) the
automatic mode function had been activated by loss of the multiplex and
hydraulic lines on April 20. In its reports prepared for BOEMRE, DNV presented
findings with respect to both of these scenarios. However, DNV concluded that
the most likely scenario for the activation of the blind shear ram was from the
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autoshear circuit.

By the time the BSR was activated and closed, the drill pipe was
positioned outside of the BSR blade surfaces. As the BSR closed, this portion of
the drill pipe became trapped between the ram block faces and prevented them
from fully closing and sealing. This resulted in a 2.8 inch gap between the
blocks, as estimated by a DNV model.

DNV concluded that, at the time of the blowout, there was a drill pipe tool
joint located between the closed upper annular and the closed upper VBR, which
the Panel concluded were properly spaced out. The Panel believes that the rig
crew manually closed the upper VBR because the upper VBR cannot be remotely
activated from the hot stab panel. During the post‐blowout well intervention

341 In its report, DNV stated that it could not rule out the possibility that the BSRs were closed
through activation of the AMF circuits.

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