[AndyTheBear]

Millisieverts are measurments of external radiation over time. Also in the news are measurments of microsieverts which are a 1000 times weaker and hardly matter so should not be confused with millisieverts. From my own recently acquired layman's understanding 4000 millisieverts is very deadly, 1000 will make you sick and a few hundred is not very good for you and will increase your chance of getting cancer later in life by some non conclusive amount.

[Rudder]

Thanks.
I'm ignorant of this stuff, so I'm dependent on what I get from web search. e.g., According to the NRC regulations, any individual member of the public should not receive more than 100 millirem per year In actuality, the effect on the public is usually less than 1 millirem per year. For comparison, a worker is allowed to receive up to 5000 millirem per year.