Much of the area burned in the massive fire that blazed through the area in 2000, and no elevated levels of radiation were detected then.
The Los Alamos facility -- the birthplace of the atomic bomb -- was shrouded in secrecy long before it was surrounded by smoke after the Las Conchas fire began Sunday.
"It contains approximately 20,000 barrels of nuclear waste," former top security official Glen Walp said. "It's not contained within a concrete, brick-and-mortar-type building, but rather in a sort of fabric-type building that a fire could easily consume.
"Potential is high for a major calamity if the fire would reach these areas," he added.
The flames from the 108-square-mile fire reportedly have reached as close as 50 feet from the grounds. With a wildfire so close, lab officials, along with government officials such as New Mexico Gov. Susana Martinez, are trying to reassure the public of the plant's safety.
"I'm confident in saying that they are committed to making it safe," Martinez told ABC News.
Thousands Evacuated, Some Remain
After a mass evacuation, the city of Los Alamos remains a ghost town. Most of its 12,000 residents were evacuated Monday, with some leaving their sprinklers on to protect their homes.
Still, according to Police Chief Wayne Torpy, about 150 die-hard residents have stayed behind, unfazed by the danger presented by their nuclear neighbor.
"I know the laboratory is secure and they're ready for this kind of emergency situation," Stephanie Chavez, a resident of Los Alamos, told ABC News.
Firefighters have made progress in the past few days, and have said that the risk of the flames reaching radioactive material is slim. Still, they cautioned that winds Wednesday could change, as could their level of confidence.
"It's a lot better that it's down," said Doug Tucker, chief of the Los Alamos Fire Department. "But we can't relax. It's better, but we can't relax quite yet."
The fire began around 1 p.m. Sunday, according to a report by InciWeb, which provides the "incident information system" and compiles information from government agencies. The report indicated that Sunday's weather conditions included high temperatures, low humidity and high winds, all of which contributed to the inferno.