The state Health Department said yesterday it was monitoring radiation levels in Hawaii as conditions worsened at Japan’s damaged nuclear reactors, and one expert warned of the possibility of airborne radiation reaching Hawaii and the West Coast in the event of a fuel rod meltdown.

The Health Department said it had not detected any elevated radiation readings in Hawaii as news came that a fourth reactor was on fire and a containment structure may have been compromised.

"I think there is a risk, certainly (to Hawaii and the West Coast)," said Paul Carroll, program director at the Ploughshares Fund, a nonprofit group that seeks a nuclear-weapons-free world.

That risk presupposes a full or partial meltdown before the Japanese succeed in getting the reactors under control.

If there is close to a full meltdown of reactor rods, "you are talking about a lot of heat," Carroll said. "You are talking about a huge, almost molten fire."

The greater the heat, the higher radiation could rise in the atmosphere, said Carroll, who has worked on nuclear weapons production and waste management issues for nearly 20 years.

"So when you get up there really high, the jet stream can catch (that radiation)," he said. "It can travel quite a distance. Ultimately, it will collect in clouds, it will precipitate to rain, and that’s what will expose you — the raindrops will carry these radionuclides down to earth."

The jet stream fluctuates in the path it takes on an easterly route, but "generally speaking, things from Japan and the Korean Peninsula are coming your way," Carroll said, meaning Hawaii.

The chairman of the Nuclear Regulatory Commission, however, said yesterday that there was a "very low probability that there’s any possibility of harmful radiation levels in the United States, or in Hawaii or in any other U.S. territories" from the Japanese reactor releases.

"You just aren’t going to have any radiological material that, by the time it traveled those large distances, could present any risk to the American public," the NRC’s Greg Jaczko said in a briefing at the White House.

Jaczko was asked to clarify that even with a reactor core meltdown — which hadn’t happened as of yesterday — there would be no chance of harmful radiation reaching Hawaii or the West Coast.

"I don’t want to speculate on various scenarios, but based on the design and the distances involved, it is very unlikely that there would be any harmful impacts," he said.

Toufiq Siddiqi, who has a doctorate in nuclear physics and is an adjunct senior fellow at the East-West Center, said yesterday that he felt that at the moment, the risk to Hawaii from the Japanese nuclear reactor radiation leaks was minimal.

"What would be the greatest concern, really, is if the containment vessels broke. Then it would be a much larger concern," Siddiqi said. "But at the moment, it seems that it is holding out."

The Health Department said it has a system in place for ambient monitoring for radioactive dust in partnership with the U.S. Environmental Protection Agency.

The system, called RADNET, looks at particulate sampling from monitors on Oahu and the Big Island that are analyzed by the Health Department and at a laboratory in Alabama. The Health Department said the "relatively small" radiation release as of yesterday was not expected to pose a public health risk to the state.

"However, should the situation change, the department is making preparations by coordinating with national and statewide partners and ensuring medical stockpiles are readily available," the Health Department said.

Department spokeswoman Janice Okubo said the state has access to the federal Centers for Disease Control and Prevention’s strategic national stockpile of medical supplies that are intended to protect the American public in the event of a health emergency.

Radioactive iodine, one concern in the event of a radiological event, can be inhaled and be absorbed by the thyroid gland. Potassium iodide can be used to block the radiation absorption in the thyroid.

Okubo said Hawaii can get a partial supply of CDC-stockpiled medicine within 12 hours and a full supply within 24 hours.