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
