We propose an RF safety assessment formalism that uses four tier levels to quantify the accuracy of SAR modeling. Each subsequent tier level consists of more modeling and validation efforts while reducing the overestimation of peak SAR levels. The lowest tier level requires no simulations or measurements whereas the highest tier level includes B1+ and thermometry-based validations. The formalism defines a safety factor to account for deviations between the simulation model and the subject adding errors with the sum-of-squares method. A tier 3 validation and error propagation procedure was conducted for a 7T prostate array.