[bahadden]

"considering one's yearly dose limit is 1 mSv total."

In Ramsar, Iran the background radition is around 200 mSv/Y (compared to a worldwide average of 2.4 mSv/Y) and _according to wikipedia_ this "high level of radiation does not seem to have caused ill effects on the residents of the area".

Call me confused.

Is the 1 mSv/Y total one of those made-up safety guidelines?

[potatolicious]

1 mSv is estimated to increase your odds of serious medical complications by 1/1,000,000. Not a significant amount, but one's regularly allowable dose should not be expected to cause health problems in the first place. Also, these limits are very conservatively set for various reasons - most of which I agree with (used to work in a nuclear facility).

So no, if you got blasted with 10 mSv all at once you shouldn't expect to vomit blood or fall over dead, but it's still a sizable amount of radiation.

Also, 400 mSv/h is 3,504,000 mSv/Y (aka 3504 Sv/Y, aka 17,000 times the radiation output in Ramsar, Iran). Of course, one doesn't expect this radiation leak to last for a whole year, but the dose rate does matter. Sucking in 400 mSv over an hour is many, many times worse than getting it over a matter of years or decades.

[beefman]

A typical CT scan will expose you to 10-15mSv. A dose of 100mSv infers a 1% lifetime cancer risk. The effects of doses as small as 1mSv are not known and are inferred by models.

[joegester]

The 1 mSv/Y guideline is based on a hypothesis that extrapolating downward from higher dosages that have well understood health effects we can infer the effects of lower dosages. They call this the Linear no-threshold model. It was chosen because it's the most conservative, safest option.

Scientists suspect that it's wrong though. We have DNA repair mechanisms that may catch many errors.

The wikipedia article (http://en.wikipedia.org/wiki/Linear_no-threshold_model) is pretty good.

[StavrosK]

Well, it's prudent to low-ball the dosages in safety guidelines.

[xiaoma]

Possibly. The largest human study ever done on the effects of chronic low-level radiation found them to be beneficial.

The researcher involved proposed a radiation hormesis model, in which the body adapts to the destructive effects of radiation by upgrading its self-repair response. US regulatory groups adhere to a linear no-threshold model in which all radiation, regardless of how weak it may be, leads to cumulative damage. It's not a resolved issue however. The French Academy of Sciences & National Academy of Medicine, for one, cited the study linked below in an argument against the LNT model.

http://www.scienceboard.net/community/perspectives.122.html

[lurch_mojoff]

The physics and physiology of radiation exposure seem to be quite complicated. I can't really answer your question, I'm very far from qualified to do so, but again _according to Wikipedia_ the short term effect of 0.2 Sv per day, let alone a year, seems to fall into the "no effect" category[1]. And according to this[2] post on Boingboing, the long term effect may not be as bad as one might think either.

[1] http://en.wikipedia.org/wiki/Sievert#Symptom_Benchmarks [2] http://www.boingboing.net/2011/03/14/radiation-dose-and-r.ht...

[brazzy]

The effects listed in the Wikipedia article refer to acute radioation poisoning, i.e. what happens when radiation is so intense that it directly kills so many of your cells that your body can't cope.

Even if at 0.2 Sv/d none of that happens, you still have a very actual, massively increased risk of cancer and genetic defects in future children. To declare "no health issues", you most definitely want to stay several orders of magnitude below that

[VladRussian]

200 mSv/Y : so that is 20 R/Y in the old language? That can not cause any ill effects only in the very specific countries, like Soviet Union, North Korea, Iran, Libya... I guess people there are just more radiation resistant.