LOS ALAMOS, N.M. -- A wildfire burning near the desert birthplace of the atomic bomb advanced on the Los Alamos laboratory and thousands of outdoor drums of plutonium-contaminated waste Tuesday as authorities stepped up efforts to protect the site and monitor the air for radiation.
Officials at the nation's premier nuclear weapons lab gave assurances that dangerous materials were safely stored and capable of withstanding flames from the 93-square-mile fire, which as of midday was as close as 50 feet from the grounds.
A small patch of land at the laboratory caught fire Monday before firefighters quickly put it out. Teams were on high alert to pounce on any new blazes and spent the day removing brush and low-hanging tree limbs from the lab's perimeter.
"We are throwing absolutely everything at this that we got," Democratic Sen. Tom Udall of New Mexico said in Los Alamos.
The fire has forced the evacuation of the entire city of Los Alamos, population 11,000, cast giant plumes of smoke over the region and raised fears among nuclear watchdogs that it will reach as many as 30,000 55-gallon drums of plutonium-contaminated waste.
"The concern is that these drums will get so hot that they'll burst. That would put this toxic material into the plume. It's a concern for everybody," said Joni Arends, executive director of the Concerned Citizens for Nuclear Safety, an anti-nuclear group.
Arends' organization also worried that the fire could stir up nuclear-contaminated soil on lab property where experiments were conducted years ago. Burrowing animals have brought that contamination to the surface, she said.
Lab officials said there was very little risk of the fire reaching the drums of low-level nuclear waste, since the flames would have to jump through canyons first. Officials also stood ready to coat the drums with fire-resistant foam if the blaze got too close.
Lab spokeswoman Lisa Rosendorf said the drums contain Cold War-era waste that the lab sends away in weekly shipments for storage. She said the drums were on a paved area with few trees nearby. As of midday Tuesday, the flames were about two miles from the material.
"These drums are designed to a safety standard that would withstand a wildland fire worse than this one," Rosendorf said.
Los Alamos employs about 15,000 people, covers more than 36 square miles, includes about 2,000 buildings at nearly four dozen sites and plays a vital role in the nation's nuclear program.
The lab was created during World War II as part of the Manhattan Project to build the atomic bomb. It produced the weapons that were dropped on Hiroshima and Nagasaki.
In the decades since, the lab has evolved into a major scientific and nuclear research facility. It works on extending the life of aging nuclear bombs, tests warheads, produces triggers for nuclear weapons and operates supercomputers and particle accelerators.
The lab also conducts research on such things as climate change and the development of a scanner for airports to detect explosive liquids. The lab's supercomputer was used in designing an HIV vaccine.
Lab officials gave assurances that buildings housing key research and scientific facilities were safe because they have been fireproofed over the years, especially since a 2000 blaze that raged through the area but caused no damage to the lab. Trees and brush were thinned over the past several years, and key buildings were surrounded with gravel to keep flames at bay.
Many of the buildings were also constructed to meet strict standards for nuclear safety, and aggressive wildfires were taken into account, lab spokesman Kevin Roark said.
"We'll pre-treat with foam if necessary, but we really want the buildings to stand on their own for the most part. That is exactly how they've been designed. Especially the ones holding anything that is of high value or high risk," said Deputy Los Alamos County Fire Chief Mike Thompson.
Teams from the National Nuclear Security Administration's Radiological Assistance Program were headed to the scene to help assess any hazards.
Lab officials said they were closely watching at least 60 air monitors for radiation and other hazards. The New Mexico Environment Department was also monitoring the air, and Udall said he asked the U.S. Environmental Protection Agency to do the same.
The lab has been shut down all week because of the fire, but authorities said the disruption is unlikely to affect any key experiments. The lab will be closed at least through Wednesday.
The wildfire has destroyed 30 structures near Los Alamos, stirring memories of a devastating blaze in May 2000 that wrecked hundreds of homes and other buildings. About 12,500 residents in and around Los Alamos have been evacuated, an orderly exit that didn't even cause a traffic accident.
Investigators do not know what sparked the fire, although suspicion has fallen on downed power lines.
The streets of Los Alamos were empty Tuesday with the exception of emergency vehicles and National Guard Humvees. There were signs that homeowners had left prepared: Propane bottles were placed at the front of driveways and cars were left in the middle of parking lots, away from anything flammable.
Some residents decided to wait out the fire, including Mark Smith, a chemical engineer at Los Alamos. He said he was not worried about flames reaching the lab's sensitive materials.
"The risk of exposure is so small," he said. "I wouldn't sit here and inhale plutonium. I may be crazy, but I'm not dumb."
Associated Press writer Barry Massey contributed to this report from Santa Fe, N.M.