Risk matrices and risk graphs are used to determine safety integrity levels for safety instrumented functions. Their simplicity makes them appealing but various difficulties militate against their use for this purpose. These difficulties include the accommodation of hazardous events, allocation of risk tolerance criteria for calibration, and consideration of overall facility risk. Layers of protection analysis and other more quantitative methods are better able to handle these issues. © 2013 American Institute of Chemical Engineers Process Saf Prog 33: 179–182, 2014