[Pinegulf]

Safe when it comes to radiation is tricky question. Since potential damage is random you might get cancer from first gamma-ray or you might survive nuclear fallout. (www.en.wikipedia.org/wiki/Daigo_Fukury%C5%AB_Maru)

However, in practice yearly 'safe' limit for civilian population is 20 mSv (ref: https://www.stuklex.fi/en/ohje/ST7-2)

The map is nSv /h. Lets take dot with 2000 nSv/h. In order to obtain yearly limit you need to hang around for 10 hours. Whereas 65000 area would be around ~20 minutes.

Please bear in mind that this is gross simplification.

[rkwasny]

You are off by 1000x:

2000 nSv/h * 10 hours = 20 μSv (microsieverts) = 0.02 mSv (millisieverts)