Nobody deems any amount of radiation to be a safe dose.  Instead, they work under a linear no-threshold model where 50 millirems each might cause 10 cancers in N million people exposed, while 200 millirems each will cause 40 cancers in the same population - absorbed dose is supposed to be directly proportional to harm in large groups of people.<p>There are <i>suspicions</i> that this is maybe too conservative, and that we have repair mechanisms for small quantities of radiation that don&#x27;t exist for larger quantities, but this directly contradicts the establishment line on the matter, and would be impossible to ethically test.<p>Placing limits on workplace or general exposure would not represent &quot;safety&quot;, but merely a threshold at which regulatory mechanisms kick in.  Per <a href="http:&#x2F;&#x2F;www.nrc.gov&#x2F;images&#x2F;about-nrc&#x2F;radiation&#x2F;factoid2-lrg.gif" rel="nofollow">http:&#x2F;&#x2F;www.nrc.gov&#x2F;images&#x2F;about-nrc&#x2F;radiation&#x2F;factoid2-lrg.g...</a> , background dose aboveground is about 310mrem&#x2F;yr, and we average about twice that when taking into account human activities (medical imaging and radon mostly, I would expect).