LOS ANGELES — The first radioactive fallout from Japan’s crippled nuclear plant reached Southern California early today, but the readings indicate levels far below a level that could endanger people, according to a diplomat.

The ambassador, who has access to United Nations radiation tracking of the Comprehensive Test Ban Treaty Organization, cited data from a California-based measuring station of the CTBTO.

Initial readings are “about a billion times beneath levels that would be health threatening,” the diplomat told The Associated Press. He asked for anonymity because the CTBO does not make its findings public.

U.S. government experts also insist there’s no threat to public health from the plume.

“Radiation is one of those words that get everybody scared, like ‘plague,'” said Dr. Jonathan Fielding, director of public health for Los Angeles County. “But we’re 5,000 miles away.”

The amount of any fallout that wafts across the Pacific Ocean to the U.S. coast will be so diluted that it will not pose any health risk, officials say. Wind, rain and salt spray will help clean the air over the vast ocean between Japan and the United States.

Nuclear experts say the main elements released are radioactive cesium and iodine. They can combine with the salt in sea water to become cesium chloride and sodium iodide, which are common and abundant elements and would readily dilute in the wide expanse of the Pacific, according to Steven Reese, director of the Radiation Center at Oregon State.

“It is certainly not a threat in terms of human health” added William H. Miller, a professor of nuclear engineering at the University of Missouri.

Earlier this week, the U.S. Environmental Protection Agency deployed extra radiation detectors throughout the country to allay public concerns. On Thursday, President Barack Obama said “harmful levels” of radiation from the damaged Japanese nuclear plant are not expected to reach the U.S.

The radiation stations will send real time data via satellite to EPA officials, who will make the data available to the public online. The monitors also contain two types of air filters that detect any radioactive particles and are mailed to EPA’s data center in Alabama.

That information, as well as samples that numerous federal agencies are collecting on the ground and in the air in Japan, also will be sent to the Department of Energy’s atmospheric radioactivity monitoring center in California, where teams are creating sophisticated computer models to predict how radioactive releases at Fukushima could spread into the atmosphere.

Inside Lawrence Livermore National Laboratory near San Francisco, scientists, engineers, and meteorological experts were analyzing those charts and maps to help policymakers predict where radioactive isotopes could travel.

“The models show what happens if the situation gets worse, if the winds change, or if it rains to predict what could happen,” National Nuclear Security Administration spokesman Damien LaVera said. “The Nuclear Regulatory Commission has said they see no radiation at harmful levels reaching the United States, and we’re not seeing anything that is inconsistent with that.”

An arm of the United Nations earlier this week made a forecast of the possible trajectory of the radioactive fallout from Japan. The forecast only showed how it might move, but does not have information about radiation levels.

The South Coast Air Quality Management District is monitoring radiation levels at its three stations every hour and planned to post daily updates on its website.

In the unlikely event that the situation escalates, the California Emergency Management Agency would coordinate emergency response efforts with state public health officials and local officials.

“Worst-case scenario, there is no threat to public health in California,” said the agency’s acting secretary, Mike Dayton.

The California Department of Public Health, which set up a hotline for concerned residents, also has its own network of eight monitors sampling the air, water, and soil for harmful substances, including radiation, said agency spokesman Ron Owens.

Farther north, in Alaska, people also have been asking where they can buy potassium iodide pills. Greg Wilkinson, a spokesman for the state Department of Health and Social Services, said the state doesn’t monitor or track private inventories, but he also said it has seen no indication that potassium iodide will need to be taken by Alaskans in response to events in Japan.

Health officials throughout the western U.S. have said there’s no need to take them.