Canadians on the West Coast are becoming more concerned about potential radioactive contamination after authorities in Japan raced to combat the threat of multiple reactor meltdowns in the quake- and tsunami-damaged northeastern coast of the country.

Officials in protective gear check Sunday for signs of radiation on children who are from the evacuation area near the Fukushima Daini nuclear plant. (Kim Kyung-Hoon/Reuters)

More than 170,000 people have been ordered out of the region, where officials fear one reactor at a power plant in Fukushima prefecture, 270 kilometres north of Tokyo, has already experienced a partial meltdown.

But an American government body just south of British Columbia has issued a statement suggesting that those on the West Coast of North America have little to fear.

The Washington State Board of Health in Olympia said on Saturday that the "nuclear event" in Japan poses no human risk in Washington state, and that officials are conducting precautionary monitoring.

"The nuclear plant incident in the wake of the earthquake in Japan has raised concerns among some people in Washington about windblown radiation coming to our state," the statement said.

"The state Department of Health is conducting ongoing air monitoring for radiation to see if the nuclear plant incident in Japan has affected radiation levels in Washington."

There have been no elevated readings so far, it said.

Even in the event of a significant release from the reactor, radiation would be diluted before reaching the West Coast, the health agency said.

"Levels would be so low no protective action would be necessary," it said.

The director of the Center for Radiological Research at Columbia University also believes that the West Coast is facing very little risk.

"It's impossible to imagine any significant radioactivity reaching the West Coast of the U.S., because it's going to get so dispersed," said David Brenner, who studies radioactive dosing and works with groups involved in planning responses to nuclear disasters.

David Measday, a nuclear physicist at the University of British Columbia, also said that even in the event of a large-scale meltdown, the radiation would dissipate over distance.

Vancouver is far enough away to avoid serious complications, he said.

Local impacts

However, it's a different story for those near the reactor site.

According to Reuters, Japanese authorities have told the United Nations Atomic Energy Commission the government is preparing to hand out iodine to residents to help protect them from exposure to radioactive iodine particles, which concentrate in the thyroid.

Besides direct exposure to radiation, the inhalation of radioactive particles poses a significant danger.

In this video image taken from NTV Japan, smoke rises from the Fukushima Daiichi nuclear power plant's Unit 1 in Okumamachi, Japan. (NTV Japan/Associated Press)

"People in the danger zones have been told to cover their mouths and noses with wet cloths," said freelance reporter Craig Dale, speaking to CBC News on Saturday.

He added there were also instructions for residents to be aware of the possibility of "internal exposure" and to avoid eating fruits and vegetables until they get the all-clear from authorities.

An explosion on Saturday at Unit 1, a reactor in the complex, injured at least four workers and destroyed the building housing the reactor, leaving only its metal frame standing. It also raised concerns that the plant would suffer a major failure.

Not Chornobyl

Though the chances of localized radioactive contamination around Fukushima is now high, nuclear physicists are saying that a Chornobyl-grade meltdown is unlikely and the likelihood of contamination reaching Canada is remote.

Brenner, on the phone from New York, said that using the word "meltdown" at all is problematic because of the range of potential meltdown events.

"Meltdown can mean different things. It could mean that just a very small amount of the top of the core has been exposed, or it could mean a lot of the core was exposed. It doesn't tell us very much to use the phrase 'meltdown,'" Brenner said.

The Fukushima crisis is a long way from a "Chornobyl," he said, because the construction and operation of the plants is different.

The Chornobyl accident 25 years ago in Ukraine spewed radiation over much of Europe after a nuclear reactor exploded and caught fire.

"The issue in Chornobyl is that they weren't able to actually stop the reactor, whereas in Japan, the reactors were certainly stopped," Brenner said.

"The other issue is that the containment vessel in Chornobyl was a lot less rugged than the ones in Japan."

The three reactors at the Tokyo Electric Power Company plant in Fukushima lost their cooling functions in the aftermath of the quake and tsunami because of a power outage.

If the Japanese are able to restore electricity and get coolant to the reactor core, the reaction will stop, Brenner said. If not, the core could breach its containment vessel and release a significant quantity of radioactivity into the environment.

"That's the thing we're most afeared of at this point," he said. "How much would depend on the actual details of how the containment core was breached."

The most likely scenario at this point is an event on the scale of the Three Mile Island accident, where a coolant failure resulted in a partial meltdown of one core in a nuclear plant in Pennsylvania in 1979.

The Chornobyl accident was the equivalent of a million Three Mile Island accidents and is still a highly unlikely scenario for a "worst case" in Fukushima, Brenner said.

The situation in Fukushima would likely fall somewhere between the two if the core containers are breached — but even then, the most severe effects would be felt only very locally.