A blown-out natural gas well blazing off Louisiana's coast poses fewer environmental dangers than past offshore accidents because it appears to primarily involve gas that disperses relatively easily, scientists said Wednesday.

"A gas well's not going to result in any kind of major pollution — perhaps not even significant pollution if it's burning," said Ted Bourgoyne, the former chair of Louisiana State University's petroleum engineering department. He now runs the consultancy Bourgoyne Enterprises Inc.

Federal inspectors said a light sheen was spotted around the rig on Wednesday evening, though authorities said it quickly dissipated and the fire aboard the rig continued to be fed by natural gas. A sheen was spotted shortly after the blowout began on Tuesday but it, too, quickly dissipated.

Gas wells often also have oil or other hydrocarbons as well as natural gas. Officials and scientists agree the latest mishap shouldn't be nearly as damaging as the BP oil spill that famously sent crude oil oozing ashore in 2010.

The fire broke out late Tuesday hours after the blowout, authorities said. Forty-four workers were evacuated from a drilling rig at the site, and no injuries were reported.

By Wednesday evening, the derrick and drill floor structure had collapsed. A fireboat was pumping water on the rig in an effort to keep as much of it as cool as possible.

University of Georgia marine scientist Samantha "Mandy" Joye also said the pollution and health dangers posed by a gas well are quite different than those posed at the well where the Deepwater Horizon rig blew up in 2010, killing 11 people and spewing millions of gallons of oil for weeks.

"The biggest danger from gas is that it is extremely flammable. At high concentration, gas exposure can cause health issues (vomiting, headaches, and worse) but such high levels are not likely to be reached in warm, shallow waters," Joye said in an email response to questions.

That's not to say there were no dangers. The Coast Guard maintained traffic restrictions within 500 metres of the site and the Federal Aviation Administration restricted aircraft up to 610 metres over the area.

Tuesday's blowout occurred at a drilling rig adjacent to a natural gas platform that wasn't producing gas at the time about 89 kilometres south of the coast. The rig was completing a "sidetrack well," which drills into the same well hole under the platform. Industry experts say such wells are used to remedy an obstruction or other problem with the original bore, or to access a different part of the gas reserve.

Gas spewed throughout the day and ignited late Tuesday night. The cause of the blowout was under investigation being overseen by the federal Bureau of Safety and Environmental Enforcement.

Rig owner Hercules Offshore Inc. said the plan to stop the flow of gas may include drilling a relief well to divert the gas from the accident site, which could take weeks.

"We are singularly focused on coming up with an action plan that would regain control over the well," said James Noe, an executive with Hercules, which was operating the rig for Walters Oil & Gas, an exploration and production company.

BSEE said the plan could be submitted for its approval as soon as Wednesday night. How long it would take to plug the well was uncertain.

Natural gas — mostly methane — is far more soluble than oil, meaning it more easily dissolves, dilutes and disperses than crude oil, said Donald Boesch, president of the University of Maryland's Center for Environmental Science and a member of the federal panel that investigated the BP oil spill. That means concentrations would be are far less lethal to the marine environment, he said.

Joye said the accident, the second blowout off the Louisiana coast this month, does raise concerns about whether more regulation is needed.

"I believe that BSEE is taking rig safety very seriously, but more active rigs gives rise to more opportunity for problems. Accidents can happen," she said.

Officials on the mainland were also concerned about whether the well fire would affect this weekend's Grand Isle Tarpon Rodeo. The major tourist event for the barrier island community of Grand Isle was cancelled after the 2010 BP oil spill.

"It's important for tourism and for the island's economy. We won't cancel it unless we have to," said event co-ordinator Angela Dorvin. Jefferson Parish Council member Chris Roberts said he expected the rodeo to go on.

Environmentalists in Louisiana said the accident proves the need for strong oversight of offshore operations.

"We won't have the oil like we did in 2010, but still this is something we need to watch closely," said Darryl Maleck-Wiley of the Sierra Club. "Once again this is highlighting the dangerous nature of oil and gas operations in the Gulf and that we need aggressive inspection programs of these operations by the federal government."