Levels of natural background radiation vary considerable, depending on location. They accepted global average is about 0.9 millisieverts per year (mSv/a), but that doesn’t mean much because there are no average locations. Wikipedia provides a chart showing background radiation levels by European country; with the ones with predominantly mountainous and rugged terrain at higher levels; Switzerland at above 4 mSv/a.
In response to the natural disaster at Fukushima in which a tsunami killed tens of thousands and left hundreds of thousands without places to live and work, the Japanese Red Cross Society has established a guideline for medical workers that sets an accumulated radiation dose limit of 1 millisievert for relief activities.
Such leaves the Red Cross workers unable to attend meetings at International Red Cross Headquarters in Geneva, Switzerland; where the annual, natural, background radiation dose is probably around 4 mSv. i.e. Four times higher than allowed for rescue workers because such radiation exposure is “dangerous”.