In order to improve the possibilities of the designer (and also of the standard setter), a simplified Markov model is presented here, which is based on a probability concept for the description of operator activities on a machine. Thus, the risk reduction effects can be scaled probabilistically, at least in the order of magnitude of the powers of ten, since no decimal accuracy can be achieved here. This makes sense, because the quantitative reliability requirements for safety functions according to ISO 13849-1 are also compared to a logarithmic scale. This paper describes how these requirements and supplementary safety measures for typical manual interventions can be assessed probabilistically. It is always a matter of reducing the probability of occurrence of hazards (and related injuries) due to technical failures as far as possible. In addition, minor errors from the previous essay will be corrected.