Preliminary results of air samples Wednesday showed no nuclear or chemical contamination, and there is now very little chance the Las Conchas Fire will move onto Los Alamos National Laboratory property, officials said Wednesday.

"What we see in this fire is exactly what see in any fire across New Mexico," LANL Director Charles McMillan said during a midday news conference regarding samples taken from one high-volume air monitor. "To me, that is very encouraging."

Later in the day, the lab issued a news release stating that preliminary results of samples taken from seven high-volume air monitors showed no air contamination.

And Wednesday night, Los Alamos County Fire Chief Doug Tucker said t preventive burns just outside the western boundary of the lab had worked.

"In my professional opinion, there is a less than 10 percent chance of spot fires on lab property this evening, diminishing tomorrow," Tucker said.

The announcements came on a day when the Los Alamos facility found itself the subject of criticism from a well-known theoretical physicist who questioned how well the lab has stored nuclear materials.

Michio Kaku, a co-founder of string theory and host of Sci Fi Science on the Science Channel, in recent days has been quoted in stories by CNN and other news outlets questioning the lab's vigilance.

On one level, remarks by a scientist of Kaku's renown demonstrate how the Las Conchas Fire and its proximity to a lab so inextricably linked to the U.S.'s bomb-making program has grabbed national and international media attention in recent days. On Wednesday night, a story about the Las Conchas Fire was on the BBC website's home page.

On another level, Kaku's remarks formed part of an ongoing conversation among some who fear the fire's ability to march onto lab property and wreak havoc with materials most of humanity knows little about.

If the fire raged out of control and burned lab buildings, Kaku told one interviewer, plutonium particulates could spew into the atmosphere and contaminate the air.

"They have to do tests on plutonium, on radioactive isotopes, and that is a cause of concern because if the fire gets really out of control, even buildings that are totally locked down could suffer a breach," Kaku told KOAT-TV earlier this week. "That is something we have to take seriously."

Kaku also questioned how the lab was storing transuranic radioactive waste at Area G. About 10,000 of the containers of low-level waste are stored above ground under fabric domes, and 6,000 are "retrievably" buried, a lab official said earlier this week. The containers have not been tested for their ability to withstand a wildfire, but the area around the containers is barren and mostly paved.

Lab officials pushed back against Kaku's pronouncements, saying the nuclear materials are very well secured.

"We are considered the world's expert on nuclear storage," LANL spokesman Kevin Roark said. "People come to us about how to do it."

The lab stores plutonium at Technical Area 55, in what is "essentially a vault" underground, Roark said.

The materials are "stored in a variety of ways, including safety-rated canisters," Roark said. "It looks like a can. It's made out of stainless steel with a high-tech lid. They vary in sizes."

The "whole facility is protected against internal fire," Roark added.

The buildings storing this material, meanwhile, are "hard concrete buildings, very sturdy," Carl Beard, the lab's principal associate director for business and operations, said during a midday news conference in Los Alamos. "They can withstand fire."

The areas also have been cleared of brush and trees that the fire could use as fuel, Beard said.

"We don't count on one layer of defense. ... It's multiple layers of defense," he said.

Contact Trip Jennings at 986-3050 or at tjennings@sfnewmexican.com.

Visit http://tinyurl.com/3grw7ft for photos of the Las Conchas Fire.