## 4 Description of the Approach
### Classification of Relevant Measures  
To integrate the identified measures into the production schedule, it is first necessary to distinguish between preventive and reactive measures in order to create a catalog of  
Figure 3: Utility functions (linear, convex, concave).  
categorized measures. The literature suggests that the main differentiator is the timing of the measure considering the occurring damage [7; 25; 29].
* Reactive measures are only used when damage has already occurred. The aim is to keep the resulting damage and the associated costs as low as possible. Due to the immediate implementation, short-term changes in the production schedule must be expected.
* Preventive measures are used to avoid potential damage and its financial impact as well as the reduction of the likelihood of occurrence. They are implemented at an early stage before the fault occurs. This excludes the possibility of changes to the production schedule with short notice.  
In addition to differentiation according to the time of implementation of a measure, economic aspects must be considered. Preventive measures should generally be preferred in the case of high expected costs for reactive measures [53]. The advantage of taking both categories of measures into account in this approach is that the preventive measures reduce the impact and likelihood of potential faults. At the same time, the planning of reactive measures creates an information base for the reactions if faults still occur, so that a solution does not have to be sought under time pressure.  
A generalized and thorough overview of relevant measures for energy-flexible production is given in VDI 5207 Part 1 [37]. The distribution of the measures within the three implementation levels of the energy-flexible factory serves as a reference point for selecting relevant measures for operational risk management (Figure 4).  
The different implementation levels in Figure 4 imply different time horizons that serve as orientation for dividing the measures into preventive and reactive. Still, for some measures it is not possible to assign them to only one category without knowing the specific production context. Thus, these measures are marked as preventive and reactive. At the short-term manufacturing level, all measures are considered reactive except for the adjustment of process parameters, which can also be an activity planned in advance. At the manufacturing control level, most of the measures available are preventive, as the regarded time horizon ranges from hours to days and thus implies longer advance planning. The manufacturing control's measures further influence the measures at the lower level, and preventive planning of these should be done whenever possible. Nonetheless, in the event of severe disruption, a job may be interrupted reactively, and, if available, energy storage  
Figure 4: Energy-flexibility measures and their classification into preventive (P) and reactive (R) measures. Figure based on VDI 5207 Part 1 [37]. Reproduced with permission of the Verein Deutscher Ingenieure e. V.  
will be used. The enterprise control level only consists of preventive measures due to the necessary longer planning horizon of days to weeks. Finally, it should be noted that this division into preventive and reactive measures is a general orientation because in the wide variety of different industries with specific planning and production systems, the respective measures may differ.