The internet is alive with questions and concerns about radiation poisoning that could result from the Japanese nukes that were damaged by the Tsunami. So to put this into perspective, perhaps some background would be helpful. Wikipedia discusses the relative exposure and dangers from release of radiation in the following:
The sievert (symbol: Sv) is the SI derived unit of dose equivalent radiation. It attempts to quantitatively evaluate the biological effects of ionizing radiation…. It is named after Rolf Sievert, a Swedish medical physicist…..
Most of you know how to read mSv but just a review for the uninitiated: mSv=0.001Sv or 1X 10^-3 or stated as milli Sv. Below you will see that eating a banana is said to dose a person with 0.0001 mSv. That is equivalent to 0.0000001Sv. If a lethal does of radiation is 10Sv, you would have to eat something like 100 million bananas in one setting.
At the other end of the scale, the lethal dose for a period of one day is 10Sv.
Single dose examples
Eating one banana: 0.0001 mSv
Dental radiography: 0.005 mSv
Avg. dose within 16 km of TMI accident: 0.08 mSv; maximum dose: 1 mSv
Mammogram: 3 mSv
Brain CT scan: 0.8–5 mSv
Chest CT scan: 6–18 mSv
Gastrointestinal series X-ray investigation: 14 mSv
Yearly dose examples
Living near a nuclear power station: 0.0001–0.01 mSv/year
Living near a coal power station: 0.0003 mSv/year
Sleeping next to a human for 8 hours every night: 0.02 mSv/yr
Cosmic radiation (from sky) at sea level: 0.24 mSv/year
Terrestrial radiation (from ground): 0.28 mSv/year
Natural radiation in the human body: 0.40 mSv/year
Radiation from granite of the US Capitol building: 0.85 mSv/year
New York-Tokyo flights for airline crew: 9 mSv/year
Atmospheric sources (mostly radon): 2 mSv/year
Total average radiation dose for Americans: 6.2 mSv/year
Smoking 1.5 packs/day: 13-60 mSv/year
Current average limit for nuclear workers: 20 mSv/year
Lowest clearly carcinogenic level: 100 mSv/year
Elevated limit for workers during Fukushima emergency: 250 mSv/year
Wiki makes clear that the severity of exposure is a function of time and amount. The following shows the effect of high levels of radiation exposure over a one day period with the likely consequences:
Symptoms of acute radiation (within one day):
0 – 0.25 Sv (0 – 250 mSv): None
1 – 3 Sv (1000 – 3000 mSv): Mild to severe nausea, loss of appetite, infection; more severe bone marrow, lymph node, spleen damage; recovery probable, not assured.
6 – 10 Sv (6000 – 10000 mSv): Above symptoms plus central nervous system impairment; death expected.
Above 10 Sv (10000 mSv): Incapacitation and death.
Another way of illustrating this data (and more) can be seen by clicking here. The blog “xkcd” has a chart demonstrating in words and pictures the relative levels of radiation exposure from small everyday experiences to death dealing levels. I recommend that you look at it because for many, it may be easier to understand than trying to relate milliSvs to Svs. The chart maker uses microSvs and those are 0.000001 Sv