News yesterday that California received minuscule amounts of radiation identified as being from Japan heightened concern over the crisis’ potential for far-reaching effects. Here are a few common questions:

Question: If radiation from Japan has reached California, what does that mean for Hawaii?

Answer: No radiation above normal background levels has been detected in Hawaii, the EPA said. Even in California the amount of radiation of Japa­nese origin was miniscule — about one-millionth of the dose that a person normally receives from the environment, the EPA said.

Q: What level of radiation is considered harmful?

A: The federal government has set an occupational limit of 5,000 millirems per year. The average person is exposed to about 600 millirems a year from watching TV, flying in airliners and from the ground itself. Cher­no­byl plant workers in 1986 received 80,000 to 1.6 million millirems; many died.

Q: If there is a severe meltdown in Japan, would people in Hawaii be at risk?

A: One expert, Donald Olander of the University of California at Berkeley, said even if there is a Cher­no­byl-like meltdown, the amount of radioactive fallout in Hawaii or the West Coast would be "barely readable" and not life-threatening because of the distance from Japan.

Q: Should I stock up on potassium iodide?

A: No, says the state Department of Health. All states have access to national stockpiles of emergency medicines and supplies. And taking potassium iodide, which is used to block absorption of radioactive iodine, is useful only if ingested close to the time of radiation exposure and could have serious side effects.