These things Stephen Davis cannot banish from his memory from that night of chaos aboard the Deepwater Horizon: the sensation of being flung into a wall by a powerful explosion, the desperate, muddy scramble on a deck lit only by the reflections from a huge pillar of flame; the look in men's eyes before they jumped 18 metres (60ft) into the water.

"You could taste the fumes, that godawful taste in your mouth," he said. "It was hard to breathe. The oxygen was being sucked out of the living quarters.

"Then all of a sudden – just boom. It was the biggest explosion I ever heard in my life."

Davis was hurled 5 metres into a wall.

"The whole rig was vibrating and shaking," he said. "It's like we walked straight into hell."

One month on from the 20 April explosion on the offshore drilling rig, the true scale of the environmental and economic destruction wrought by a gushing oil well in the Gulf of Mexico has yet to entirely unfold.

Scientists have yet to establish a firm estimate of how much oil and gas is spewing into the Gulf from the geyser on the ocean floor, or to determine its future course.

Stephen Davis survivor of the Deepwater Horizon oil platform explosion. Photograph: guardian.co.uk

Heavy patches of crude reached the marshes of Plaquemines, Louisiana this week and the Obama administration admitted the oil had got caught up in the powerful loop current, where it could reach the coral reefs of the Florida Keys.

Once in the current, the oil could travel as far as Mexico or Cuba, Frank Muller-Karger, an oceanographer at the University of South Florida, told Congress this week.

For Davis, the events of that night, when the rig exploded killing 11 of the 126 crew, was only the beginning of his ordeal. He says he and other survivors were to spend the next 40 hours in isolation – barred from phoning their families – while his lawyers believe Transocean, the owners of the rig, readied its legal defences. Seventeen crew members were seriously injured in the incident.

For Barack Obama, whose officials are being held to account for their oversight of offshore drilling in congressional hearings this week, the disaster could be the defining event of his presidency.

For the companies involved in the disaster – BP, the well owner, Transocean, the rig owner, and subcontractors Halliburton and Cameron – that night was only the beginning of what lawyers predict will be one of the longest and most complicated court battles the US has ever seen.

"This will be one of the biggest torts probably in the history of the United States," said Anthony Buzbee, a Houston lawyer who is representing Davis and nine other survivors who are seeking $5.5m (£3.7m) each in damages from Transocean and other firms. "These cases will be going on for many, many years." He said he was preparing litigation against two other firms who supplied equipment to the rig.

The day of 20 April had started like any other for Davis, a 36-year-old native of San Antonio, Texas. He spent most of his 12-hour shift in the centre of the rig, welding the transporter platform for the blowout preventer (BOP).

Investigators see the failure of that safety device, which sits on the ocean floor, as one of the causes of the disaster. As Davis went off shift, he overheard an engineer say he was going to try to relieve the pressure on the BOP.

Davis ate dinner, phoned his fiancee and son, worked out in the gym and returned to his quarters in the lower level of the rig.

During all that time – about three hours – he heard loud hisses as engineers worked to reduce the pressure building up from the ocean floor. Later, this would strike him as odd as relieving pressure is usually achieved quickly.

He had been in bed watching TV for about 15 minutes when he heard the first bang. Initially he thought a crane might have dropped a piece of casing or a boom. Then the rig started shaking and the lights went out. He put a lifejacket on over his shorts and T-shirt, grabbed his tennis shoes and ran into the hallway.

Davis has been working on offshore rigs for seven years but had only been on the Deepwater Horizon four days. He did not know his way around. "My comfort zone was really small," he said. He had made it part way up the stairs towards the lifeboats on the middle deck when the walls caved in.

Davis found another staircase. On deck, screaming workers were sliding through mud, looking for their designated lifeboats. The reserves of helicopter fuel and diesel caught fire and exploded.

"People were panicking," he said. "They would look at you and just jump into the water. You could understand why if you looked behind you and saw all these explosions, you would think you were either going to burn up or jump."

Davis made it to lifeboat No 1. It was an 18 metre drop to the water and the lifeboat was overloaded, but the vessel did not capsize and its pilot guided it safely to the rig's supply vessel, the Damon Bankston. He watched the Deepwater Horizon burn from there.

"We actually watched the derrick [a lifting device] melt from the starboard side of the rig as they airlifted the guys out. It was horrid, it was overwhelming, it was unbelievable."

By Davis's estimate, it took 12-15 minutes to get from the rig to the work boat, but it would take another 36-40 hours before they were to return to shore – even though there were dozens of boats in the area and Coast Guard helicopters airlifting the most severely injured to hospital.

Some of the men were openly furious, while others, like Davis, were just numb. He says they were denied access to the onboard satellite phone or radio to call their families.

When the ship finally did move, it did not head for shore directly, stopping at two more rigs to collect and drop off engineers and coast guard crew before arriving at Port Fourchon, Louisiana.

The company was ready for the men then, with portable toilets lined up at the dock for drug tests. The men were loaded on to buses, given a change of clothing and boxes of sandwiches, and taken to a hotel in Kenner, Louisiana, where finally they were reunited with their families.

Lawyers say the isolation was deliberate and that Transocean was trying to wear the men down so they would sign statements denying that they had been hurt or that they had witnessed the explosion that destroyed the rig.

"These men are told they have to sign these statements or they can't go home," said Buzbee. "I think it's pretty callous, but I'm not surprised by it."

Davis had been awake nonstop for about 50 hours by that point. He signed. Buzbee says most of the men did.

But that is unlikely to limit the lawsuits against the companies involved in the disaster. In addition to survivors, Buzbee is representing more than 100 oystermen, fishermen and seafood packers who are seeking economic damages.

"Anyone whose livelihood depends on the water is going to have some sort of damage," he said. Dozens of other lawyers are also assembling cases.

For Davis, though, it is still too early to think about his next step. Will he ever set foot on a rig again? He can't say. "For now, I'm just numb."