Jinx999 Wrote:The BBC website considers it headline news that "Radiation levels at a quake-stricken Japanese nuclear plant reach levels harmful to human health". However it doesn't explain exactly what they mean by that. My initial suspicion is that it means "radiation levels have reached a level that will result in a statisitically detectable increase in your chance of getting cancer if you live there for at least a couple of decades".There are two considerations when you're exposed to any sort of harmful anything.. One is acute exposure. How much can you be exposed to anything in a short time (say within 8 hours) before you start suffering effects (possibly irreversible). The other is long term exposure. How much can you absorb over a longer period of time before effects start showing up in the future (like cancer)?
For ionizing radiation here are the guidelines
What are the limits of exposure to radiation?The
Threshold Limit Values (TLVs) published by the ACGIH (American
Conference of Governmental Industrial Hygienists) are used in many
jurisdictions occupational exposure limits or guidelines:
20 mSv - TLV for average annual dose for radiation workers, averaged over five years
1 mSv - Recommended annual dose limit for general public (ICRP - International Commission on Radiological Protection).
What effects do different doses of radiation have on people?
One sievert is a large dose. The recommended TLV is average annual dose of 0.05 Sv (50 mSv).
The
effects of being exposed to large doses of radiation at one time (acute
exposure) vary with the dose. Here are some examples:
10 Sv - Risk of death within days or weeks
1 Sv - Risk of cancer later in life (5 in 100)
100 mSv - Risk of cancer later in life (5 in 1000)
50 mSv - TLV for annual dose for radiation workers in any one year
20 mSv - TLV for annual average dose, averaged over five years
Note that TEPCO has pushed the limits to 250mSV for their workers, so figure 12.5 in 1000 chance of cancer later in life.
http://www.ccohs.ca/oshan...hys_agents/ionizing.html
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