Quantitative risk assessment may be integrated by means of human reliability analysis, which assesses the probability of human failure events by evaluating the influence of underlying factors on human performance. A step-by-step tutorial for the application of a human error quantification technique is presented in this chapter. However, the application of this technique should be preceded by a thorough qualitative analysis of the tasks performed by the operator/crew in the scenario considered. As an example of application, the analysis of a scenario of drive-off of a semisubmersible drilling unit is studied. This demonstrates how to account for issues of human–machine interface, stress, shortage of time, and rare-event experience, which may lead the operator into failure and increase the probability of an accident.