Ships monitoring BP's broken oil well stood fast Friday as the remnants of Tropical Storm Bonnie blew toward the spill site, threatening to force a full evacuation that would leave engineers clueless about whether a makeshift cap on the gusher was holding.
Vessels connected to deep-sea robots equipped with cameras and seismic devices would be among the last to flee and would ride out the rough weather if possible, retired Coast Guard Adm. Thad Allen said.
"If conditions allow, they will remain through the passage of the storm," Allen said in New Orleans.
Bonnie made landfall south of Miami early Friday as a feeble tropical storm with top sustained winds of 64 kph. It broke apart as it crossed Florida and was a tropical depression as it moved into the Gulf, but forecasters expected it to strengthen slightly and roll over the spill site around midday Saturday.
The ships holding the robots would be among the first to return if forecasts force them to leave, but they could be gone for up to two days, said Allen, the federal government's spill chief.
The mechanical plug that has mostly contained the oil for eight days will be left closed, Allen said, but if the robots are reeled in, the only way officials will know if the cap has failed will be if satellite and aerial views after the storm passes show oil pooling on the surface.
Audio surveillance gear left behind could tell BP whether the well is still stable, but scientists won't be able to listen to the recordings until the ships return to the area.
Allen expressed increasing confidence in the experimental cap despite a few leaks that initially worried government experts. Scientists say even a severe storm shouldn't affect the plug, nearly 1.6 kilometres beneath the ocean surface 64 kilometres from the Louisiana coast.
"There's almost no chance it'll have any impact on the wellhead or the cap because it's right around 1,524 metres deep and even the largest waves won't get down that far," said Don Van Nieuwenhuise, director of professional geoscience programs at the University of Houston.
Crews of other vessels, including one boring the tunnel meant to kill the flow of crude for good, spent Friday pulling up their gear and getting out of the storm's way. Workers were pulling up 1.6 kilometres of pipe in 12-metre to 18-metre sections and laying it on deck of the drilling rig so they could move to safer water, probably to the southwest flank of the storm.
"Preservation of life and preservation of equipment are our highest priorities," said Allen, a veteran of the Coast Guard's rescue mission after Hurricane Katrina.
Shell Oil was also evacuating its operations in the Gulf, moving out more than 600 workers and shutting down production at all but one well sheltered safely in Mobile Bay.
At the spill site, the water no longer looks thick with gooey tar. But the oil is still there beneath the surface, staining the hulls of boats motoring around in it.
Strong winds and waves could help break up the oil further, but a storm surge also might push it into sensitive marsh areas along the coast.
"Those are two opposite consequences and we're prepared to move out and aggressively attack this once the threat has passed through," he said.
The foul weather has stalled progress toward killing the well and could delay until mid-August the sealing of the nearly 3.2-kilometre underground shaft using mud and cement, Allen and BP say. BP had hoped to finish drilling a relief tunnel Friday, but had to plug it Wednesday to prepare for the storm.
Before the cap was attached and closed a week ago, the broken well spewed 355 million litres to 696 million litres into the Gulf after the BP-leased Deepwater Horizon rig exploded April 20, killing 11 workers.
Also Friday, an electronics technician told an investigative panel that an alarm system was partially shut down the day the ill-fated oil rig Deepwater Horizon exploded in the Gulf of Mexico.
Later, the House Energy and Commerce Committee, which is investigating the spill, asked Transocean Ltd. for documents concerning safety and the condition of equipment on the rig. Transocean owned the rig, which was being leased by BP PLC. BP is responsible for cleaning up the millions of gallons of oil that have seeped into the Gulf.
Technician Mike Williams told the panel that the alarm system was turned on to monitor for fire, explosive gas and toxic gas but that its sound and light alarms had been disabled. Williams said he was told the company didn't want a false alarm waking people at night.
