Stage 1 represents the starting point of the evaluation (corresponding to Level 0) It refers to cases where it is expected that the annual dose (committed effective dose from intakes of radionuclides that occur in the accounting year) is likely to be below 0.1 mSv, even if there were similar intakes in each and every monitoring interval during the year. At this level there is no need to evaluate the intake or dose from the measured values explicitly. The effective dose can be reported as zero, by analogy with the rounding of doses in external dosimetry. However, the measured value should be recorded, because it may provide information useful for further assessments in the future.

Step 1.1: Identify monitoring value (M) and duration of monitoring interval (T). Some treatment of the data may be required before an evaluation can be made. In particular consideration should be given to the presence of other radionuclides, as well as that measured (the indicator nuclide), which may add significantly to the dose, or even exceed that from the radionuclide measured.

Step 1.2: Compare measurement with critical monitoring quantity M_c. If M < Mc then the annual dose is probably less than 0.1 mSv. The evaluation stops and the measured value M is recorded together with all relevant information (radionuclide, activity, type of measurement, type of monitoring etc). Note that measurements of actinides are typically above M_c and so there is no need to compare those measurements explicitly with the corresponding critical monitoring quantity.

Step 1.3: Exposure above Level 0. Since M > M_c the annual dose could be more than 0.1 mSv. Go to Stage 2 to check on the statistical significance of the measurement.