A long-awaited report by the US Chemical Safety Board has concluded that malfunctions in the blind shear ram of the blowout preventer at BP's fateful Macondo well helped worsen the deadly 2010 explosion and spill.
The CSB report released on Thursday found that the shear ram, a last-resort mechanism in the blowout preventer designed to slice through the drillpipe to cut off the flow of oil, did indeed activate the night of the spill, earlier than estimated in other reports.
But the agency found that high pressure in the drill pipe caused it to buckle off-centre, and as a result the component did not work as planned.
"Instead of cleanly cutting and sealing the well’s drill pipe, the shear ram actually punctured the buckled, off-center pipe, sending huge additional volumes of oil and gas surging toward the surface and initiating the 87-day-long oil and gas release into the Gulf that defied multiple efforts to bring it under control," the CSB said in the investigation.
"The report concludes that under certain conditions, the 'effective compression' phenomenon could compromise the proper functioning of other blowout preventers still deployed around the world at offshore wells."
The agency also concluded that "two instances of miswiring and two backup battery failures" impacted the electronic and hydraulic controls of the blowout preventer.
The CSB produced a detailed animation of the findings, which can be found here.
A spokeswoman for UK supermajor BP said the CSB analysis agreed with its contention that multiple factors were to blame for the incident, but the latest report contained "theories based upon flawed assumptions".
"These theories ignore the physical evidence and testing performed during the BOP’s forensic examination and are contrary to the conclusions reached by other investigations.
"Moreover, no party other than Transocean has ever concluded that the AMF/deadman worked despite the maintenance deficiencies."
Transocean told Upstream the latest report affirmed its internal investigations as well as others completed by government and independent exports, according to spokesman Lou Colasuonno.
"The CSB report confirms that the Deepwater Horizon BOP had been tested successfully in accordance with regulatory requirements and activated as intended at the time of the incident, but was unable to seal the well because immense pressure buckled the drill pipe and prevented the blind shear ram from functioning as designed," Colasuonno said.
However Transocean said it disagreed with the CSB's criticism of its safety culture as well as its jurisdiction to evaluate the incident as the US National Transportation Safety board is chiefly tasked with marine spills.
Since the 2010 spill the US has overhauled its offshore regulatory regime, rolling out a raft of new regulations intended to strengthen safety practices, but the CSB contends additional action is needed.
“More must be done to ensure the correct functioning of blowout preventers and other safety-critical elements that protect workers and the environment from major offshore accidents,” CSB chairman Rafael Moure-Eraso said in a statement.
The US Bureau of Safety and Environmental Enforcement (BSEE) has been developing a blowout preventer rule for some time of which it intends to release a draft copy by year's end.
"The comprehensive reforms, which strengthen requirements for everything from well design and workplace safety to corporate accountability, are helping ensure that the United States can safely and responsibly expand development of its domestic energy resources," said BSEE chief of public affairs David Smith.