"I saw mud falling on the back of my boat, sort of a black rain," said Alwin Landry, standing watch on the support vessel Damon B. Bankston.
Landry told a federal inquiry into the April 20 explosion and the deaths of 11 crewmen that he immediately radioed the bridge of the rig when the mud rained down and was told something had gone wrong.
"I was advised they were having trouble with the well ... I heard the concern in the voice of the operator," Landry said, and he ordered his crew to disconnect a hose tethering his ship to the Deepwater Horizon.
Suddenly, a green flash on the main deck of the rig behind the derrick caught his eye, then the concussion of the initial blast.
Crewmen of the Bankston were able to rescue the 115 surviving workers from the Deepwater, including some who leaped into the Gulf to escape the flaming rig.
One of the last off the rig, Landry said, was Curt Kuchta, the Deepwater Horizon's captain, who told him he'd try to hit a "kill" switch, a device that would shut down dangerous systems prone to combustion.
"He pressed it and didn't know if it worked or not," Landry said.
Anthony Gervaso, the engineer aboard the Bankston, said he learned from his captain that rig workers had advised they were going to start "displacing the riser," meaning it would be removing mud that helped contain pressure deep in the drillshaft.
If true, that would be an unusual move because, commonly, two plugs are cemented into the hole to contain pressure before mud is removed. In the Deepwater Horizon well, only one cement seal had been set.
Gervaso described how he was part of the rescue effort from a smaller boat, driving around the rig and plucking survivors from the water. Later, he testified, he overheard some Deepwater Horizon crewmen on the deck who thought a dome of explosive gas had come out of the derrick, settled over the rig on the calm night and got sucked into machinery, leading to the ignition.
"Because it was so calm out, it accumulated in the engine room, that the engine room had caught fire, blown up," he said.
Earlier, Kevin Robb, a civilian Coast Guard rescue specialist, told investigators that crews following computer generated search patterns spent 80 hours after the blast looking for survivors in the 67-degree water before calling off the search.
"What you're looking for is roughly the size of volleyball, a person's head," Robb said.
Coast Guard ships and helicopter criss-crossed a grid roughly the size of Connecticut in the search, Robb said.