New Orleans (US), May 12 (DPA) Government regulators are not required to conduct independent reviews of an oil rig's blow-out preventer, the fail-safe mechanism that failed to seal off the well that is now spewing crude oil into the Gulf of Mexico, it was revealed Tuesday.

The blow-out preventer (BOP) became a hot topic during the first public hearings into what caused the April 20 explosion of the Deepwater Horizon oil rig off the Louisiana coast.

The BOP should have activated automatically following the blast, sealing the deepwater well's opening at the sea floor. It is unclear why the mechanism failed to activate.

Frank Patton, who reviews drilling permits in the New Orleans district for the Minerals Management Service (MMS), admitted that the government agency simply required oil companies themselves to certify that their blow-out preventer meets regulatory standards.

"They certify that they are in compliance" with the government's standards, Patton said, noting that he had rarely visited a rig to supervise tests of the BOP.

The acknowledgment prompted a rare moment of open critique from Hung Nguyen of the US Coast Guard, co-chair of the government's internal investigation into the explosion along with MMS.

"We have self-certification for some of these critical pieces of equipment," Nguyen complained, suggesting this might be one of the reforms put in place to prevent another disaster.

The public hearings in Kenner, Louisiana, near New Orleans, were part of an investigation ordered by President Barack Obama to uncover the cause of the April 20 disaster and recommend reforms.