Frequently asked questions
Taking human action into account in risk control measures

Is it possible to assign a high confidence level (NC) to a human MMR or SAMS?

The NC allocated to a MMR involving human action is generally limited to one level (NC = 2), and this level is generally associated with the upper limit of the probability of failure, i.e. 1E-2. In practice, to justify a NC = 2, the operator will be asked to provide detailed arguments, or, for example, to apply the OMEGA 20 method. As a general rule, MMRs involving human action are allocated a NC = 1, except in the special case of relatively simple actions and/or those for which the operator is trained and instructed (e.g.: switching on an AU in the control room in response to an alarm).

Is it possible to enhance the value of several man-made barriers in the same scenario?

Yes, provided that the independence of the barriers is verified. For example, we need to make sure that the operators involved in...