[en] The research program of the Physics Division's tandem Van de Graaff accelerator facility at Argonne National Laboratory often requires entries into a target room while the accelerator beam is present, both to perform adjustments on an experiment in progress and to set up a future experiment on another beam line. To assure the safety of personnel, while permitting the maximum feasible freedom of movement, it is useful to have a means of predicting the maximum possible radiation levels in the target room for the planned operating conditions. This would assure thorough radiation surveys, by Health Physics personnel, when they are needed, while minimizing delays for low hazard experiments. Such a predictive index has been developed by John P. Schiffer, a Senior Physicist, at Argonne National Laboratory. It is called the Heavy Ion Radiation Criterion (HIRC). The authors have performed an empirical study of the effectiveness of the HIRC. From July, 1978 to May, 1979, the actual, measured radiation levels for accelerator experiments were compared with the calculated HIRC values. For each experiment, the radiation level used was the maximum measured dose equivalent rate (gamma plus neutron), in mrem/h. The results of these measurements are given