System safety is considered as one of the most important non-functional requirements for safety-critical embedded systems. Several safety assessment methods have been proposed to evaluate safety-critical systems. However, most of them cannot be used to assess safety-critical design patterns due to the fact that these patterns do not address real systems but present abstract solutions to commonly recurring design problems. This paper introduces a proposal for a safety assessment method for safety-critical systems design patterns. This method includes a safety metric based on the computation of the relative safety improvement achieved when using the design patterns under consideration. A Monte Carlo based simulation method is used to illustrate the new proposed assessment method which allows to compare them with respect to their impact on safety.