The iec 61508 standard series defined a framework for quantification of functional safety. for each particular industry sector, specific standards are being developed based on it. this framework is well suited for electrical and electronic components. however, in the field of machinery, control systems are realized not only by such components, but also by mechanical, pneumatic and hydraulic components, which exhibit a different failure behavior. such components are considered by the iso 13849 standard. however, quantification methods of this standard are still not quite well understood by the users, and have strong limitations. this work presents a study an alternative method of how to calculate the average frequency of dangerous failures (pfh), required by iso 13849 in order to achieve a performance level (pl). this alternative method includes modeling safety functions as reliability block diagram and evaluation of pfh using the software blocksim, through discrete event simulation. modeling hypothesis and limitations are discussed. the proposed method enables calculation of the standard’s cases, as well as consideration of different failure distributions, of which weibull distribution is considered. a study case considering weibull distributed failures is presented. applicability of the method is also discussed.