EPA/DHS/FEMA Radiation Exposure Limits for Responders

The general rule was always 10 REM to protect valuable property necessary for the public welfare and 25 REM for lifesaving operations. 

While there is all sorts of speculation on REM limits are the specific sources.

Protective Action Guides and Planning Guidance for Radiological Incidents (USEPA)

https://www.epa.gov/sites/production/files/2015-06/documents/pag-manual-interim-public-comment-4-2-2013.pdf

Protective Action Guides for Radiological Dispersal Device (RDD) and Improvised Nuclear Device (IND) Incidents (DHS/FEMA)

http://hps.org/govtrelations/documents/dhs_pags_fr.pdf