FACTBOX: How much radiation is dangerous

TOKYO: Japan has encouraged local authorities to make more frequent checks of the radiation after the explosions at two nuclear reactors, with reports of radiation levels at nine times the normal short detected in Kanagawa near Tokyo. Below are some facts about the health risks associated with higher levels of radiation.
* Japan Chief Cabinet Minister Yukio Edano said radiation levels near the affected plant in north-eastern coast up to 400 millisieverts (mSv) per hour, thousands of times higher than that of before the explosion. That would be 20 times the current annual level for some nuclear industry workers and uranium miners.
* Exposure to 350 mSv was the criterion for the resettlement of people following the Chernobyl accident,
According to the World Nuclear Association.
* People are exposed to natural radiation of about 2 mSv per year.
* Crew airline flights to New York, Tokyo polar route are up to 9 mSv per year.
* Exposure to 100 mSv per year is the lowest level at which any increase in cancer is evident. Cumulative 1000 mSv is probably the cause of fatal cancer many years later in five out of every 100 people exposed to it.
* One 1000 mSv dose causes radiation sickness such as nausea, but not death. A single dose of 5000 mSv would kill about half of those exposed to it for a month.
* "It is very acute radiation, like what happened in Chernobyl, and Japanese workers at nuclear power plants, it is unlikely for the population," said Lam Ching-Wan, chemical pathologist at the University of Hong Kong Kong.-Reuters