The blaze has been growing by tens of thousands of acres a day. It’s close to surpassing New Mexico’s largest fire, the Dry Lakes fire. That blaze charred more than 94,000 acres in the Gila National Forest in 2003.

Crews have managed to contain only 3 percent of the fire near Los Alamos. They’re bracing for winds that could gust up to 40 mph Thursday afternoon.

Fire information officer Sandra Lopez says crews are dealing with rugged, steep country, hot temperatures and erratic winds.

Officials at the nuclear laboratory that created the first atomic bomb say it could be a few days before they know how experiments have been affected by a shutdown forced by the wildfire. Teams will quickly figure out where things stand as soon as they're able to return, said Charles McMillan, the lab director at the Los Alamos National Laboratory, which sits atop desert mesas in eastern New Mexico. There was no word on when it will reopen, but it was expected to remain idle at least through Friday.

The lab has been shut down since Monday, when all of the town of Los Alamos and some of its surrounding areas — 12,000 people in all — were evacuated.

The government sent a plane equipped with radiation monitors over the lab. Samples analyzed so far from some of the lab's monitors show nothing abnormal in the smoke. Authorities and outside experts on nuclear engineering expressed confidence that the blaze would not scatter radioactive material. “The nuclear materials are secure,” said Penn State University nuclear engineering professor Barry Scheetz, who has served on National Academy of Sciences nuclear review boards and has been to Los Alamos several times.

“There's multiple redundancy in the protection of this material.”

Anti-nuclear groups have sounded the alarm about thousands of 55-gallon drums containing low-grade nuclear waste — gloves, tools, even paper notes and other contaminated items — about 3 km from the fire.

Lab officials said it was highly unlikely the blaze would reach the drums, and that the steel containers can in any case withstand flames and will be sprayed with fire-resistant foam if necessary.

The lab works on such topics as renewable energy and particle physics, solar flares, forensics on terrorist attacks, and studying the AIDS virus at the molecular level to help scientists develop strategies for developing vaccines.

The lab also did early work on the human genome project.

At quadrillions of calculations per second, the Cielo supercomputer has enough computing power to simulate nuclear explosions based on models from previously collected data.

“When we get fine enough resolution we start to see physics occurring that we know has to be there,” McMillan said.

McMillan said he's limited on details of most of the experiments because they involve work to secure the US nuclear stockpile.

Meanwhile, the economic impact of shutting down the town was already weighing on the minds of Los Alamos officials and business owners. Following a major wildfire in May 2000, the federal government paid out tens of millions to hundreds of businesses to compensate for financial and property loss.

Gov. Susana Martinez said the state is helping by delaying collection of sales taxes from business affected by the fire.