The dose limit in any unrestricted area from external radiation sources shall not exceed 2 mrem (0.02
mSv) in any one hour. In addition operations shall be conducted such that radiation exposure to
individual members of the public shall not exceed 100 mrem (1 mSv) in a year. It shall be noted that
the definition does not limit the radiation exposure to a particular rate (such as 2.5 mR/hr), but
permits higher exposure rates PROVIDING that the total quantity of radiation in any unrestricted
area during any one hour does not exceed 2 mrem (20 mSv) and during any calendar year does not
exceed 100 mrem (1 mSv) to any single individual.
Special consideration must be given to assure that restricted areas are of sufficient size as to preclude
adverse impact on adjacent operations. Assure that qualified experts are consulted prior to initiation
of operations if in doubt.
Table 6-25 provides summary data comparing the measured exposure rate with the maximum
allowable on time (in minutes per hour) of the radiation source so that the total dose in any one hour
does not exceed 2 mrem.
Maximum Permissible Dose Rate Versus Hourly Duty Cycle
Measured Exposure Rate
Total Time X-ray Machine (or Gamma-ray Source) Is
Operated During a One-Hour Period (minutes)