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Japan’s Radiation Crisis and Human Health: Understanding Radiation Levels

Updated on September 30, 2011

The level of radiation at the Fukushima Daiichi nuclear power plant in Japan is currently (on 3/18/11) 400 millisieverts.  The International Atomic Energy Agency  (IAEA) provides up to date briefings on the current status at Fukushima and the current levels of radiation.  Recent articles from Harvard Health Publications help explain how much radiation this is and how much radiation is safe. 

Sievert (Sv) is pronounced SEE-vert, and is a measure of the biologic effect radiation has on people and how much harm it can cause.  A millisievert (mSV) is a thousandth of a sievert.  A microsievert is a millionth of a sievert.  Americans use a different measure known as a rem.  One sievert equals 100 rem and a millisievert equals 100 millirem.

In order to get a good grasp of what these numbers mean, it is helpful to compare 400 milliseiverts/hour or 40,000 rems/hour to other, more familiar sources of radiation, such as a chest x-ray.    The chart below shows visually how the current radiation levels compare, and shows the level of radiation at which radiation sickness begins.  Of course, the situation has not yet been stabilized, so the current levels are subject to change.  The IAEA link can be used to get current levels.

Chest X-ray
Two-view Mammogram
Average Annual Background Exposure in the US
Cardiac nuclear stress test
CT scan of the abdomen
Coronary angiogram
Average exposure of evacuees from Belarus after 1986 Chernobyl disaster
Annual dose limit* for nuclear power plant workers (*as set by the US Nuclear Regulatory Commission)
Spike recorded at Fukushima Daiichi nuclear power plant
400 per hour
40,000 per hour
Acute radiation sickness begins
1,000 (or 1 sievert)
Sources: U.S. Environmental Protection Agency, Health Physics Society, U.S. Nuclear Regulatory Commission, International Atomic Energy Agency

More Facts About Radiation Exposure

  • A person would need to be exposed to at least 100 mSv a year to have an increase in cancer risk. Exposure to 1,000 mSv during a year would probably cause a fatal cancer many years later in five out of every 100 people.
  • Total body CT scan: about 10 mSv.
  • Mammogram: about 0.7 mSv.
  • CT colonography: about 5 to 8 mSv.
  • CT heart scan: about 12 mSv.
  • Typical chest X-ray: about 0.02 mSv
  • Dental X-ray: 0.01 mSv
  • .Coast-to-coast airplane flight: about .03 mSv. Airline crews flying the New York-Tokyo polar route are exposed to 9 mSv a year.

Sources: Reuters; New England Journal of Medicine; American Cancer Society; World Nuclear Association and Taiwan's Atomic Energy Council

In addition to the dose of radiation, it is important to consider the length of time a person is exposed at that dose. If a person is exposed to 400 millisieverts/hour they are exposed to that dose for an hour. If a person is exposed to 400 millisieverts but only for a half hour, then their exposure is 200 millisieverts. If the person is exposed for one minute, their exposure is 6.6 millisieverts/minute. If they were exposed at that level for 7.5 minutes their exposure would be 50 millisieverts of radiation, which is the maximum allowable radiation level for US nuclear power plant workers for an entire year.

Another way to understand the numbers is to consider radiation exposure during a chest x-ray. A person is exposed to 0.1 millisievert of radiation during a chest x-ray, but the exposure only lasts a tenth of a second. If the x-ray machine was left on for 6.5 minutes while the person stood in front of it, the exposure would be 400 millisieverts of radiation after 6.5 minutes.

Radiation levels decrease as a person moves away from the source. Tokyo is 150 miles from Fukushima. While levels of radiation in Tokyo are higher than usual, they are far below the levels that would cause risk to human health. So, the farther from the source the better. Currently, in the US, there is no human health risk from the radiation being emitted from the Fukushima Daiichi nuclear power plant in Japan. Contamination could occur if items are shipped to the US from the immediate area or by persons travelling from the area. A decontamination protocol will need to be established to ensure radiation levels are safe for travel and export.

Fukushima Daiichi nuclear power plant:
Fukushima, Fukushima Prefecture, Japan

get directions

Tokyo, Japan

get directions

United States:
United States

get directions

More About Sieverts, Millisieverts and Measuring Radiation


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    • kimh039 profile imageAUTHOR

      Kim Harris 

      7 years ago

      Refer away, fetty:)....and feel free to come back and post a link to your CD here. I appreciate your very specific feedback. Sometimes I re-read my hubs and notice ways to make them simpler and more clear; and then change them. I like to read recent research on topics I understand, and then try to make the information more interesting and understandable to more people. In this case, I wanted to understand the situation better myself!

    • fetty profile image


      7 years ago from South Jersey

      kimh039 - Thank you for the comparisons as well. I would like to refer people to this hub. I have posted info. about a double CD produced by Sony as a fund raiser for these poor people. The interest is just not there. Would that be OK with you? My post is in the Entertainment category under Music. Thanks. Great hub. You always pack your hubs with amazing research that is easily understood. You have a great talent!

    • kimh039 profile imageAUTHOR

      Kim Harris 

      7 years ago

      glad you stumbled in, healthyhanna. That will be an interesting web page. understanding radiation levels helped me understand the severity of the problem. let me know when you finish your page.

    • HealthyHanna profile image


      7 years ago from Utah

      Enjoyed this hub. I am researching the effects of nuclear fallout for my web page.

    • kimh039 profile imageAUTHOR

      Kim Harris 

      7 years ago

      My pleasure, Tony:) I hoped it would be helpful - both in understanding the numbers and easing some of the anxiety we all get we don't understand a threat.

    • tonymac04 profile image

      Tony McGregor 

      7 years ago from South Africa

      Thanks for putting this informative material together. I find it very helpful.

      Love and peace


    • kimh039 profile imageAUTHOR

      Kim Harris 

      7 years ago

      Thanks Seeker and Vern. I come back every once in a while with a "beginner's mind" to make sure it still makes sense to me, too! I keep wanting to add some other ideas to it, and then decide not to. I think with this one, less is better!

    • vrbmft profile image

      Vernon Bradley 

      7 years ago from Yucaipa, California

      Hi Kim

      Excellent hub. I have a difficult time writing this kind of "piece" so I really appreciate you doing the job and an excellent one. We are being bombarded with information about the problem, so it is very helpful to read something that is both informative and accurate. THANKS.


    • Seeker7 profile image

      Helen Murphy Howell 

      7 years ago from Fife, Scotland

      Very interesting hub and written in a way that I could grasp the facts that I found confusing reading other articles on this subject. Many thanks.

    • kimh039 profile imageAUTHOR

      Kim Harris 

      7 years ago

      Thanks Tony and dahoglund. It helped me to compare to an x-ray, CT scan or a mammagram, and I could see how the current levels compared to what nuclear workers are allowed to be exposed to and what levels make you sick. I had never heard of sievert or rem before, and now I at least have a sense of what that is. Once I made a little sense of it, I thought I'd pass it along.

    • dahoglund profile image

      Don A. Hoglund 

      7 years ago from Wisconsin Rapids

      up and useful. The comparisons are helpful in understanding. I can at least compare to some exposure that I have had like x-rays and scans.

    • Tony DeLorger profile image

      Tony DeLorger 

      7 years ago from Adelaide, South Australia

      Informative Hub. Thanks Kim, didn't get the numbers before.


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