There is no simple answer to the question as to how much radiation is safe or how much is dangerous.

Low levels carry some risk, and high levels can be quickly fatal, but there is no clear dividing line.

As a CRUDE guide a dose of one Sievert is likely to be fatal, and one tenth of that dose carries significant risk.

One Sievert=one thousand milli Sieverts, or one million micro Sieverts.

Consider a dose rate of ten micro Sieverts per hour, that is many times normal background levels, but is of little short term danger.
10 micro Sieverts an hour if continued for 10,000 hours is a total of 100,000 micro Sieverts. That is one tenth of a Sievert, a significant risk. 10,000 hours is just over a year.

The same dose rate for 1,000 hours would carry some risk, a small risk by wartime or emergency conditions, but still far, far in excess of the dose and consequent risks allowed in peacetime for workers in a nuclear power plant, or nuclear weapons facility.

A lot depends on the general health of the victim, and on what medical care is available.