ISO/TR 13849-3:2026

Safety of machinery — Safety-related parts of control systems — Part 3: Markov model-based PFH calculation

Scope

This document provides formulas for the estimation of the PFH value of single-channel architectures as well as two-channel architectures with and without diagnostics in accordance with ISO 13849-1. The formulas presented in this document are based on Markov modelling and can be used as an alternative to the simplified procedure of ISO 13849-1 for estimating the quantifiable aspects of the performance level (see ISO 13849-1:2023, 6.1.8, Figure 12, and Annex K). They can also serve as an alternative to any other adequate method for estimating the quantifiable aspects of the performance level.
NOTE            Different estimation methods can vary in the resulting PFH values due to their nature. A certain variation is usually the consequence of different modelling approaches and unavoidable simplifications specific to the method.
Other requirements of ISO 13849-1, e.g. on categories or software, are not addressed by this document.