An investigator who examined the safety device that failed to prevent last year’s BP oil spill said Monday his firm did not skip critical tests under pressure to meet a deadline to file a report on what caused the contraption not to work.

Neil Thompson, a Det Norske Veritas vice president, told a federal investigative panel that tests that were removed would not have affected the determination of why the blowout preventer failed.

DNV’s March 23 report concluded the device failed because of faulty design and a bent piece of pipe.

“We don’t believe that conclusion would change,” Thompson said.

The report appears to shift some blame for the disaster away from the oil giant and toward those who built and maintained the 300-ton safety device. It was built by Cameron and maintained by Transocean.

At least one outside expert has said the findings cast serious doubt on the reliability of all other blowout preventers used by the drilling industry.

BP and the U.S. Chemical Safety Board argue more testing should have been done before conclusions were reached. Cameron argues backup data should have been given to the parties when the report was filed.

Documents emerged early in the probe showing that a part of the device had a hydraulic leak, which would have reduced its effectiveness. There were also concerns raised about batteries in the control pods used with the blowout preventer and a “deadman” trigger that is supposed to activate the device when power to the rig is lost.

Gary Kenney, the lead investigator assigned by DNV to handle the blowout preventer analysis, testified Monday that testing showed low battery function in one of the control pods and inconsistent power function to operate a component of the other control pod. But he said those issues were dismissed as primary contributing factors to the blowout preventer failure.

Kenney acknowledged that not all of the functions of the blowout preventer stack were tested.

Under intense cross-examination from a Cameron attorney, Thompson acknowledged that a final DNV computer model of where the pipe was believed to have lodged inside the blowout preventer was not completely accurate. He also acknowledged he has no operational experience on a drilling rig and had never laid eyes on a blowout preventer before being asked to participate in testing the device used with BP’s Macondo well.

Among other things, Thompson said DNV did not consider whether any damage to the side sealing packers on the blowout preventer may have contributed to the device’s failure.

The blowout preventer report by the Norwegian firm DNV was not the final word on the Deepwater Horizon disaster that killed 11 workers and led to more than 200 million gallons of oil spewing from a BP well a mile beneath the Gulf of Mexico.

Monday’s testimony came during the seventh round of hearings before the joint U.S. Coast Guard-Bureau of Ocean Energy Management Regulation and Enforcement investigative panel, which is looking into the causes of the April 20, 2010, rig explosion and oil spill off Louisiana. The panel expects to release some preliminary findings a few days before the anniversary of the disaster later this month.

Also Monday, Rep. Henry Waxman, D-Calif., and Rep. Diana DeGette, D-Colo., urged the Chemical Safety Board and BOEMRE to examine whether the length of time Transocean’s workers were on the rig at the time of the explosion contributed to the disaster.

They said documents they have been provided indicate that Transocean shifted from a 14-day-in-a-row rig worker schedule to a 21-day-in-a-row schedule in the months before the explosion. The members of Congress said they were told this was partially a cost-saving measure.

Neither of the federal agencies would comment. Transocean said in a statement that the 21-day schedule benefits employees and the company through continuity of operations, reduced crew travel and longer on-shore intervals that allow for more comprehensive training.