CHARLESTON, W.Va. (AP) — Speed doesn't appear to have been a factor in an oil-train derailment in southern West Virginia, a federal transportation official said Thursday.

The CSX train was going 33 mph at the time of Monday's crash in the town of Mount Carbon. The speed limit was 50 mph, said Federal Railroad Administration acting administrator Sarah Feinberg.

"We can see from event recorders that the train was traveling below speed limit and starting to accelerate at time of derailment," Feinberg said.

The train had gone through the town of Montgomery minutes earlier where the speed limit was 30 mph, she said.

The derailment shot fireballs into the sky, destroyed a house, leaked oil into a Kanawha River tributary and forced nearby water treatment plants to temporarily shut down. The owner of the destroyed home was treated for smoke inhalation. No other injuries were reported.

The cause remains unknown. Investigators had reviewed video from cameras on the front and rear of the locomotives as well as a train coming from the opposite direction. But the footage showed nothing significant.

"You can clearly see and hear where the derailment takes place," Feinberg said.

Twenty-seven of the 107 tank cars derailed, and 19 of those were involved in the fires, which continued smoldering Thursday.

The small fires have prevented investigators from gaining full access to the crash scene. Feinberg said it might be necessary to use a dry chemical to douse the fires, out of worry that using water or spray foam would wash oil into the river.

Robert C. Lauby, the railroad agency's chief safety officer, said oil must first be pumped out of damaged tank cars before they can be removed — a process slowed by weather-frozen hoses and pumps. The removal of the damaged cars is likely to start Friday, he said.

No rail cars entered the river and no oil has been detected in river water samples, according to a joint statement from several agencies that have responded to the derailment. Water treatment systems were brought back online Tuesday, and a boil-water advisory for area residents expired Thursday.

A road leading to the derailment site remained closed, preventing about 225 people from returning to 100 homes, said Coast Guard Lt. Scott McBride, speaking on behalf of the agencies.

"We're working on a plan to possibly reopen that road because residents are getting itchy to get back to their homes," he said.

Amtrak, whose Chicago-to-New York Cardinal route travels along the same tracks where the derailment occurred, has been told by CSX that the tracks won't reopen until early next week, said Amtrak spokesman Marc Magliari in Chicago.

The CSX train was bound for an oil-shipping depot in Yorktown, Virginia, along the same route where three tank cars plunged into the James River in Lynchburg, Virginia, last year, prompting an evacuation.

"We at the Department of Transportation and in the administration understand the gravity of this issue," U.S. Transportation Secretary Anthony Foxx told The Associated Press on Thursday.

That's why the department chose to craft a rule that not only deals with the question of tank car design, but also with operational issues that could prevent accidents, such as lower speeds and better braking and emergency response after an accident occurs, he said.

"It's an approach that pushes the country forward on all fronts," Foxx said.

The department finished drafting final rules and sent them to the White House budget office earlier this month. The budget office is supposed to complete reviews of regulations within 120 days, but often takes many months longer. Federal officials are prohibited from publicly discussing the details of the proposals until the rules are made final.

Some of these measures would cost billions more and have been strongly opposed by the oil and rail industries.

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Associated Press writers Joan Lowy in Durham, North Carolina, and Matthew Brown in Billings, Montana, contributed to this report.