The “bladder effect.”

That was the theory offered by BP’s top two supervisors who were onboard the Deepwater Horizon oil drilling rig on April 20, 2010, to explain why they didn’t react with alarm when they saw the results of a critical pressure test used to determine whether the ill-fated Macondo well was properly sealed.

It wasn’t, of course, and the men, Donald Vidrine and Robert Kaluza, were slammed in a 2012 federal indictment for misinterpreting the test results and ignoring clear warning signs that the well was in danger. A grand jury charged them with 11 counts apiece of seaman’s manslaughter and involuntary manslaughter, along with violating the federal Clean Water Act.

But U.S. District Judge Stanwood Duval Jr. last year dismissed the seaman’s manslaughter charges, ruling the statute is meant to be applied to a captain or someone tasked with operating and navigating a vessel, rather than supervisors of a drilling operation. In what could be a key legal skirmish, federal prosecutors on Wednesday will try to persuade a three-judge panel of the U.S. 5th Circuit Court of Appeals to reinstate the charges.

The murky status of the case against Kaluza and Vidrine, coupled with the recent setting aside of a guilty verdict against former BP engineer Kurt Mix, has revived questions about the federal government’s efforts to hold individuals criminally liable for the Gulf of Mexico oil spill disaster — which not only cost 11 lives but is considered the nation’s worst environmental disaster.

Legal experts note with disappointment that the years-long investigation netted only a handful of indictments, mostly against rank-and-file employees, and some of those appear to be on shaky ground.

“There are obviously multiple causes of the tragedy, but the most significant from my vantage point was the corporate culture at BP that emphasized profits and risk-taking over environmental protection and safety,” said David Uhlmann, a law professor at the University of Michigan and former head of the Justice Department’s Environmental Crimes Section.

Nonetheless, high-level BP executives who helped fuel the admittedly negligent practices that led to the disaster have remained mostly unscathed.

The only top executive in the government’s sights is David Rainey, BP’s former vice president of exploration for the Gulf, who awaits trial on obstruction charges for allegedly lying to Congress about how much oil was gushing from the busted well. But even Rainey’s alleged misdeeds, Uhlmann notes, had nothing to do with BP’s safety culture.

“It’s hard to understand how Robert Kaluza and Donald Vidrine are the primary individual culprits,” Uhlmann said. “They had supervisory authority on the rig, which is why their conduct should be scrutinized, but they had no role in creating the corporate culture that was the primary cause of the Gulf oil spill.”

Convenient fall guys?

When Vidrine and Kaluza were charged in November 2012, U.S. Attorney General Eric Holder boasted the indictments would serve as a warning to companies and their employees who play fast and loose with safety. But both men, as well as Mix, have maintained essentially the same defense: that the government needed someone to take the fall, and they were most convenient patsies.

In Uhlmann’s view, the federal government is “in a difficult position, because if all they do is bring charges against corporations, the question is fairly raised: Why is there no individual accountability?”

But he has some sympathy for Vidrine and Kaluza, too.

“When the individuals you charge are at such low levels at some of the largest corporations in the world, it’s fair to ask whether those individuals are scapegoats for conduct that took place above them in the corporate hierarchy,” he said.

Vidrine, who lives in Lafayette, refused to testify in hearings after the spill to assess what went wrong, citing medical problems. Kaluza invoked his Fifth Amendment right against self-incrimination. In court filings, both men have maintained their innocence.

Some experts believe the ultimate success of the government’s case against them will hinge on whether the seaman’s manslaughter charges are reinstated. That statute requires a lower burden of proof to show negligence, said Blaine LeCesne, a law professor at Loyola University who has analyzed the criminal and civil cases stemming from the disaster.

LeCesne believes the charges will be reinstated. Even though Kaluza and Vidrine weren’t in charge of navigating the rig, “they were responsible for the well-being of those in that vessel, and it was arguably their inattention that led to the deaths of those people,” he said. “They were at the epicenter of that flawed decision-making, and they had the final say with respect to what should’ve been done.”

A fatal decision

After the failed pressure test, the drilling rig’s crew began removing heavy drilling fluid from the riser — the mile-long pipe connecting the well at the ocean floor to the drilling platform on the surface — and replacing it with lighter seawater. It was a fatal decision, allowing oil and explosive natural gas to flow freely up the well and onto the rig floor. Before long, the well blew out, igniting the drilling rig and causing it to explode.

Eleven men were killed, and millions of barrels of crude oil were spewed into the Gulf of Mexico, into wetlands and onto beaches of the Gulf Coast.

Apart from the handful of individuals charged, the federal prosecution of the case has aimed largely at the companies involved, including BP; Transocean Ltd., which owned the rig and supplied the crew to BP; and Halliburton, hired to design and pump the cement to plug the well before it could be developed for production.

There’s little dispute that the failure by Vidrine and Kaluza to correctly interpret the pressure test had disastrous consequences. Their actions were the subject of much of the first phase of an eight-week federal civil trial in New Orleans, when attorneys and federal prosecutors argued over which of the firms involved in the ill-fated drilling project should be held liable.

Richard Heenan, an independent drilling consultant, testified during the trial on behalf of the federal government that the handling of the pressure test “was a gross and extreme departure from the standards of good oil field practices.”

The rig’s crew believed the test was in fact successful, based on the notion of a so-called bladder effect, which they said occurred when pressure on valves produced false readings in the drill pipe. But Heenan said in his expert report that the bladder effect — which the two men cited as a reason for not sounding the alarm — “has no technical basis, and the adoption of that theory demonstrates the abdication of responsibility of both BP and Transocean.”

The ‘well from hell’

Kaluza, who spent 35 years in the oil and gas industry, had been assigned to the Deepwater Horizon just four days before the blowout, filling in for its regular well-site leader, who left for training onshore. Kaluza had no idea what he was getting into, according to his lawyer, former federal prosecutor Shaun Clarke. “Unknown to Mr. Kaluza, he was being sent to what others had called the ‘well from hell,’ the ‘trouble,’ the ‘nightmare,’ ” Clarke wrote in a court filing.

Vidrine is also represented by a former federal prosecutor, Robert Habans Jr.

If convicted, each man faces a maximum of eight years for each count of involuntary manslaughter and up to a year in prison on the Clean Water Act count. Each count of seaman’s manslaughter carries a possibility of 10 years in jail.

Their appeals hearing comes a month after Duval ordered a new trial for Mix, a former BP engineer found guilty last year of obstruction of justice for deleting a string of text messages in an alleged effort to hamper the government’s criminal investigation of the oil spill. Mix was the first of five defendants charged in connection with the spill to be tried. So far, just one man has been convicted: Anthony Badalamenti, a former Halliburton manager who was sentenced to probation for destroying evidence in the wake of the accident.

Duval, in a strongly worded order, vacated Mix’s guilty verdict based on an interview Mix’s lawyer conducted with a juror after the trial, which revealed juror misconduct.

The same day that Vidrine and Kaluza were indicted, BP itself agreed to plead guilty to 11 counts of felony manslaughter, obstruction of Congress and a series of environmental crimes, and to pay a $4 billion fine.

Transocean has also agreed to pay $1.4 billion in civil and criminal fines and penalties, mostly to resolve federal Clean Water Act civil penalty claims, while Halliburton pleaded guilty to a misdemeanor charge of destroying evidence and will pay a maximum $200,000 fine, serve five years of probation and donate $55 million to the National Fish and Wildlife Foundation.

Follow Richard Thompson on Twitter, @rthompsonMSY.