4 ms·

The limit is 50mSv per year, not per hour. Sievert is cumulative unit that has to be either qualified by time or measured over entire lifespan to be meaningfull

by dfox 11y ago

The limit is 50mSv per year, not per hour. Sievert is cumulative unit that has to be either qualified by time or measured over entire lifespan to be meaningfully comparable. But on the other hand quantitatively measuring and comparing radiation effects is hard problem as there is essentially nothing that can be precisely measured and at the same time has any meaning as to biological effects, in practice the conversions between various units are just done using various experimentally determined constants that may or may not be relevant to given situation.

e12e 11y ago
Would appear that the limit is similar - the "red zone" is for "(> 50 mSv/y)" (note "more than") -- and the sign at the end "Leaving the zone" reads 4.9 mSV/h. That'd be about 42.000 mSV/year -- if we assume constant dose. Or put it another way -- stay an hour and you're at the (safe) limit of exposure for a year. As for all the comments on how nuclear isn't all that dangerous -- how much do we really know about people leaving 4-5 generations in an area with elevated radiation, eating produce etc? I guess we have some data from the Bikin Islands[1] -- but those levels might very well be much higher -- at least it's not an example of how we can live safely in a radiation zone. Speaking of [1]: "The special International Atomic Energy Agency (IAEA) Bikini Advisory Group determined in 1997 that "It is safe to walk on all of the islands ... although the residual radioactivity on islands in Bikini Atoll is still higher than on other atolls in the Marshall Islands, it is not hazardous to health at the levels measured ... The main radiation risk would be from the food: eating locally grown produce, such as fruit, could add significant radioactivity to the body...Eating coconuts or breadfruit from Bikini Island occasionally would be no cause for concern. Eating many over a long period of time without having taken remedial measures, however, might result in radiation doses higher than internationally agreed safety levels." IAEA estimated that living in the atoll and consuming local food would result in an effective dose of about 15 mSv/year." It will be interesting to see if removing topsoil in Fukushima will be enough for radiation to reach safe levels. Hopefully the water tables are safe. [1] https://en.wikipedia.org/wiki/Nuclear_testing_at_Bikini_Atoll#Return_to_Bikini_Island https://en.wikipedia.org/wiki/Nuclear_testing_at_Bikini_Atol...
- dfox 11y ago
  The main radiation hazard is not in the actual exposure to radiation, but in ingestion (in the broad sense, including inhalation) of radioactive isotopes. Such contaminants are able to remain inside the body for long times and have various long time effects that are more severe than acute radiation exposure. That is one reason why radiation (even measured in sieverts) is not really meaningful measure.
- 542458 11y ago
  It's actually not clear how low doses of radiation over a long period of time affect human health. Estimates and standards are usually built assuming that a short, intense dose and a long, slow dose are the same as long as they contain the same quantity of radiation (the Linear no-threshold model). However, there is doubt about how valid this is for long-term doses. There are a few places on earth that have naturally high radiation levels (up to 250mSv/year), including many places with large granite deposits or hot springs. However, these places often do not show any higher cancer incidence (or other relevant health problems) than other areas, possibly suggesting some sort of limit before radiation becomes harmful (the Threshold model). Some studies actually show significantly lower cancer incidence than other areas. This has prompted the idea of Radiation hormesis, that low doses above background have some benefit. We do know that low doses do stimulate cell repair mechanisms in different ways than large doses do, so it does seem possible (although real-world data is mixed). The effects are not well understood at present, and it's an area that is under ongoing study. Unfortunately, it's an absolute devil to research!
- ggreer 11y ago
  The numbers in your first paragraph are off by a factor of 1,000. The signs are in microsieverts per hour, not millisieverts. Only the author's peak reading of 6.8µSv/h would have exceeded the maximum for radiation workers, and only if he stood in that spot for a whole year. Even then, it would still be below the lowest dosage that is clearly linked to increased cancer risk (100mSv/year).
  - e12e 11y ago
    You're right of course. I didn't realize that was a greek letter on the sign in the photo. Still, ~43[1] mSv/year is pretty close to the "safe" limit (and it makes sense to set a safety limit well below what can be documented as being harmful) -- and that's just from irradiation. Who knows the effect of breathing in pollen, never mind eating local produce, over a period of ~50 years? Are there different safety levels for children/infants? If the 50mSv/year is set for workers, I assume they're for adults? [1] I accidentally dropped a significant digit when rounding off too. It comes to ~42924.0, not ~49...
magila 11y ago
All of the radiation figures in the article are in mSv per year, not per hour.
- dfox 11y ago
  Photos of various signs in the article are in uSv/hour.

by dfox 11y ago

e12e 11y ago

Would appear that the limit is similar - the "red zone" is for "(> 50 mSv/y)" (note "more than") -- and the sign at the end "Leaving the zone" reads 4.9 mSV/h. That'd be about 42.000 mSV/year -- if we assume constant dose. Or put it another way -- stay an hour and you're at the (safe) limit of exposure for a year. As for all the comments on how nuclear isn't all that dangerous -- how much do we really know about people leaving 4-5 generations in an area with elevated radiation, eating produce etc? I guess we have some data from the Bikin Islands[1] -- but those levels might very well be much higher -- at least it's not an example of how we can live safely in a radiation zone. Speaking of [1]: "The special International Atomic Energy Agency (IAEA) Bikini Advisory Group determined in 1997 that "It is safe to walk on all of the islands ... although the residual radioactivity on islands in Bikini Atoll is still higher than on other atolls in the Marshall Islands, it is not hazardous to health at the levels measured ... The main radiation risk would be from the food: eating locally grown produce, such as fruit, could add significant radioactivity to the body...Eating coconuts or breadfruit from Bikini Island occasionally would be no cause for concern. Eating many over a long period of time without having taken remedial measures, however, might result in radiation doses higher than internationally agreed safety levels." IAEA estimated that living in the atoll and consuming local food would result in an effective dose of about 15 mSv/year." It will be interesting to see if removing topsoil in Fukushima will be enough for radiation to reach safe levels. Hopefully the water tables are safe. [1] https://en.wikipedia.org/wiki/Nuclear_testing_at_Bikini_Atoll#Return_to_Bikini_Island https://en.wikipedia.org/wiki/Nuclear_testing_at_Bikini_Atol...

dfox 11y ago
The main radiation hazard is not in the actual exposure to radiation, but in ingestion (in the broad sense, including inhalation) of radioactive isotopes. Such contaminants are able to remain inside the body for long times and have various long time effects that are more severe than acute radiation exposure. That is one reason why radiation (even measured in sieverts) is not really meaningful measure.
542458 11y ago
It's actually not clear how low doses of radiation over a long period of time affect human health. Estimates and standards are usually built assuming that a short, intense dose and a long, slow dose are the same as long as they contain the same quantity of radiation (the Linear no-threshold model). However, there is doubt about how valid this is for long-term doses. There are a few places on earth that have naturally high radiation levels (up to 250mSv/year), including many places with large granite deposits or hot springs. However, these places often do not show any higher cancer incidence (or other relevant health problems) than other areas, possibly suggesting some sort of limit before radiation becomes harmful (the Threshold model). Some studies actually show significantly lower cancer incidence than other areas. This has prompted the idea of Radiation hormesis, that low doses above background have some benefit. We do know that low doses do stimulate cell repair mechanisms in different ways than large doses do, so it does seem possible (although real-world data is mixed). The effects are not well understood at present, and it's an area that is under ongoing study. Unfortunately, it's an absolute devil to research!
ggreer 11y ago
The numbers in your first paragraph are off by a factor of 1,000. The signs are in microsieverts per hour, not millisieverts. Only the author's peak reading of 6.8µSv/h would have exceeded the maximum for radiation workers, and only if he stood in that spot for a whole year. Even then, it would still be below the lowest dosage that is clearly linked to increased cancer risk (100mSv/year).
- e12e 11y ago
  You're right of course. I didn't realize that was a greek letter on the sign in the photo. Still, ~43[1] mSv/year is pretty close to the "safe" limit (and it makes sense to set a safety limit well below what can be documented as being harmful) -- and that's just from irradiation. Who knows the effect of breathing in pollen, never mind eating local produce, over a period of ~50 years? Are there different safety levels for children/infants? If the 50mSv/year is set for workers, I assume they're for adults? [1] I accidentally dropped a significant digit when rounding off too. It comes to ~42924.0, not ~49...

magila 11y ago

All of the radiation figures in the article are in mSv per year, not per hour.

dfox 11y ago
Photos of various signs in the article are in uSv/hour.