## 3 Classification of Leading Indicators  
A schematic summary of the results shown in the previous sections could be the following: Two categories of indicators are considered in [13]: (i) process integrity indicators; (ii) and occupational risks indicators. Three categories of indicators are proposed in [12]: (i) management and organization indicators; (ii) process safety indicators; (iii) occupational safety indicators. And in the SMEs context [19] two categories on OSH performance indicators are identified: management and organization indicators; and individual OSH indicators. A pyramidal structure with four levels of process safety indicators is considered in [27]: Loss of Primary Containment (LOPC) Events of Greater Consequence; LOPC \begin{table}
\begin{tabular}{c c c} \hline \hline \multicolumn{3}{c}{**Indicator Typology**} \\ \cline{2-3}  & **Class I** & **Class II** \\ \hline United States Nuclear Regulatory Commission work & \(\bullet\) & \(\bullet\) \\ Accident sequence precursor-based indicators & \(\bullet\) & \(\bullet\) \\ Resilience-based early warning indicators & \(\bullet\) & \(\bullet\) \\ Operator-specific safety indicators & \(\bullet\) & \(\bullet\) \\ Performance indicators defined by the World Association of & \(\bullet\) & \(\bullet\) \\ Nuclear Operators & \(\bullet\) & \(\bullet\) \\ Operational safety indicators & \(\bullet\) & \(\bullet\) \\ Safety performance indicators & \(\bullet\) & \(\bullet\) \\ Probabilistic indicators & \(\cdots\) & \(\bullet\) \\ Probabilistic safety assessment-based risk indicators & \(\cdots\) & \(\bullet\) \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Examples of indicators Class I and II or approaches for their development (Adapted from [5]). Figure 1: Proactive approaches to assess organizational factors’ effect on safety/risk (Adapted from [5; 20]). Events of Lesser Consequence; Challenges to Safety Systems; and Operating Discipline & Management System Performance Indicators. Considering the previous schematic summary in an integrated way, a structure of indicators emerges configured of three categories organized in two levels as shown in the Figure 2. Conceptually following to [27]: the categories occupational risks and process integrity are associated with an incident with greater consequence resulting from actual losses of containment and loss of primary containment events with a lesser consequence but may be predictive; category integrated management represent challenges to the safety systems and provides an opportunity to identify and correct weaknesses within the safety system. At the first level of said structure, it is established by the indicators of the management system which can be integrated, as shown symbolically in the Figure 2. The second level is configured of two categories of interrelated indicators, that is, process integrity indicators and occupational risks indicators. In turn, each of these three categories has two dimensions. As for the first dimension, it represents the direction of the indicator, that is, leading or lagging indicator. Regarding the second dimension, the risk nature, that is, emerging or traditional risk, it can be determined by paying attention mainly to the consequence variable, according to the criteria exposed in [7; 28]. From all this, a classification of indicators as shown in the Figure 3 is derived. More specifically, a classification of leading indicators also is derived as shown in the Table 5. This table shows the direction of the leading indicators as well as qualitative graduation of the potential associated consequences, following the concept considered in [27]. These consequences have been graded with greater intensity when the risk is an emerging risk.