A qualitative and category-based method of safety integrity level (SIL) assignment. Risk graph analysis uses four parameters to make a SIL selection: consequence, occupancy, probability of avoiding the hazard, and demand rate. Each of these parameters is assigned a category and a SIL is associated with each combination of categories. In some cases, quantitative tools, such as LOPA, are used to assist the analyst in determining which category to use, but typically the assignment is done qualitatively. Using the selected categories, the analyst follows the resulting path that leads to the associated SIL assignment.