I think they mean 620mREM. 620 rem would easily kill you even if spread out over a year.
1OOO MSV is indeeed 100 Rem! In the USA, ppl get through the year, 6.2 MSV, which is 620 Rem. Read the math here: http://en.wikipedia.org/wiki/Sievert#SI_multiples_and_conversions
The dose that makes sense is the Banana equivalent Dose. Because of Potassium 40, eating a banana is about the same as being exposed to 3,000 some odd pico curies.
permitted exposure is very safe: One working level month in uranium mines is exposure to 100 pico curies, or like eating 1/30th of a banana. Normal eating of bananas is part of your background radiation. Max dose of anyone at 3 mile island was 1/75th of a banana.
How much is bad for you?
Annually
you get about 200-300 millirem or 0.2 to 0.3 rad, most from natural radon gas. Bananas and other Potassium 40 is about 20 millirems of that. 20 millirems is 0.020 rem
OSHA limit is 5 rem per year
Acute dose
Nausea at ~100 Rads or 110 Rem
LD 50 is at 450 to 500 Rads half the people who get this die
LD 100 is at 600 Rads all the people who get this die
http://www.osha.gov/SLTC/radiationionizing/introtoionizing/ionizinghandout.html
bump