Flaws in safety equipment and procedures used on Gulf of Mexico (GoM) rigs persist four years after 11 workers died in an explosion aboard the Deepwater Horizon that led to the largest offshore oil spill in U.S. history.

Drillers and regulators misunderstand the limits of BOPs, which are supposed to pinch pipes and prevent oil and natural gas from escaping a well in an emergency, the U.S Chemical Safety and Hazard Investigation Board said in a report made public June 5. The BOPs on BP’s Macondo well failed, causing millions of gallons of oil to spew into the GoM in April 2010.

Industry practice and federal safety rules currently in place in the GoM may not prevent another catastrophic spill, according to the report. U.S. regulations fall short of standards used for drilling off the coasts of Norway, Australia and the U.K., which require more rigorous, regular and independent safety-equipment checks, the agency said.

“Vital aspects of effective safety critical element management have not been established in the U.S. offshore,” the report concluded. “Deficiencies identified during the failure analysis of the Deepwater Horizon BOP could still remain undetected in BOPs currently being deployed to well heads.”

Each system in the five-story-tall BOP must be tested individually so that a properly operating backup system doesn’t mask failure of another, according to the report. A pre-deployment test of the Deepwater Horizon BOP failed to reveal that two backup systems were wired improperly, investigators said.

Government reaction

The government halted deepwater exploration drilling in the GoM for five months after the Macondo disaster. The agency that oversaw offshore drilling was split to improve safety and enforcement and regulations were strengthened to prevent recurrence.

“There’s nothing here that hasn’t already been exhaustively addressed by regulators and the industry,” Brian Straessle, a spokesman for industry group the American Petroleum Institute, said in an e-mail. “The report ignores the tremendous strides made to enhance the safety of offshore operations.”

The safety board, which typically investigates chemical and refinery disasters, found that well-control manuals still in use by BP and Transocean Ltd. recommend a procedure that can cause drill pipe to buckle and jam the blowout preventer, as happened at Macondo.

BP costs

“We respectfully disagree with other findings in the report, including and especially the CSB’s assertions regarding Transocean’s operational and safety culture,” Lou Colasuonno, a spokesman for Transocean, said in a statement. Ellen Moskowitz, a spokeswoman for London-based BP, didn’t immediately respond to an e-mailed request for comment.

BP booked $42.7 billion of expenses after the blowout aboard Transocean Ltd.’s drilling rig. Last month, the London- based company lost an appeal seeking to erase disputed payments connected to a $9.2 billion settlement with most private parties. It still faces as-yet unassessed fines for the spill and environmental damage.

The report was done at the request of House lawmakers to probe the causes of the Macondo disaster.